0001564590-21-055440 | 10-Q | XBRL Viewer

Accumulated other comprehensive loss

569,835

292,348

(58)

(2)

Total Cullinan stockholders' equity

(126,395)

(93,339)

443,386

199,010

Noncontrolling interests

2,088

1,304

Total stockholders' equity

445,474

200,314

^[2]

Total liabilities and stockholders' equity

$ 453,404

$ 214,708

[1]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	34,900,878
Common stock, shares issued	43,660,909	29,831,125
Common stock, shares outstanding	43,660,909	29,831,125

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)
$ in Thousands

3 Months Ended

9 Months Ended

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2021

Sep. 30, 2020

^[1]

Income Statement [Abstract]

Revenue

$ 18,943

Type of revenue [Extensible List]

us-gaap:LicenseMember

Operating expenses:

Research and development

$ 12,680

$ 9,913

$ 36,873

$ 26,582

General and administrative

5,695

1,586

15,677

4,580

Total operating expenses

18,375

11,499

52,550

31,162

Loss from operations

(18,375)

(11,499)

(33,607)

(31,162)

Other income (expense):

Interest income

118

185

340

809

Other income (expense), net

(2)

(12)

Net loss

(18,259)

(11,314)

(33,279)

(30,352)

Net loss attributable to noncontrolling interest

(909)

(1,456)

(223)

(6,899)

Net loss attributable to common stockholders of Cullinan

$ (17,350)

$ (9,858)

$ (33,056)

$ (23,453)

Net loss per share, basic and diluted

$ (0.40)

$ (0.50)

$ (0.76)

$ (1.21)

Total weighted-average shares used in computing net loss per share, basic and diluted

43,438,861

19,721,992

43,254,230

19,453,479

Comprehensive loss:

Net loss

$ (18,259)

$ (11,314)

$ (33,279)

$ (30,352)

Comprehensive loss attributable to noncontrolling interest

(144)

(56)

Comprehensive loss

(18,202)

(11,458)

(33,335)

(30,289)

(909)

(1,456)

(223)

(6,899)

Comprehensive loss attributable to Cullinan

$ (17,293)

$ (10,002)

$ (33,112)

$ (23,390)

[1]

The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)
$ in Thousands

Total

Common Stock

Noncontrolling Interest in Subsidiaries

Additional Paid-In Capital

Accumulated Other Comprehensive (Loss)/Income

Accumulated Deficit

Balances at Dec. 31, 2019

^[1]

$ 97,865

$ 2

$ 864

$ 138,543

$ (4)

$ (41,540)

Balances, shares at Dec. 31, 2019

^[1]

18,738,734

Issuance of common stock equivalents net of issuance costs of $213

^[1]

14,037

Issuance of common stock equivalents net of issuance costs, shares

^[1]

1,297,700

Balances at Mar. 31, 2020

(5,163)

(190)

(4,973)

106,769

$ 2

674

152,580

(46,513)

Balances, shares at Mar. 31, 2020

20,036,434

Balances at Dec. 31, 2019

^[1]

97,865

$ 2

864

138,543

(4)

(41,540)

Balances, shares at Dec. 31, 2019

^[1]

18,738,734

Balances at Sep. 30, 2020

^[2]

(30,352)

89,511

$ 2

1,863

152,580

(64,993)

Balances, shares at Sep. 30, 2020

20,036,434

Balances at Mar. 31, 2020

106,769

$ 2

674

152,580

(46,513)

Balances, shares at Mar. 31, 2020

20,036,434

Issuance of subsidiary common stock

175

Noncontrolling interest acquired in MICA

5,673

177

Balances at Jun. 30, 2020

(13,875)

(5,253)

(8,622)

98,919

$ 2

1,269

152,580

203

(55,135)

Balances, shares at Jun. 30, 2020

20,036,434

Issuance of subsidiary common stock

844

Issuance of subsidiary preferred stock

1,206

(144)

Balances at Sep. 30, 2020

(11,314)

(1,456)

(9,858)

89,511

$ 2

1,863

152,580

(64,993)

Balances, shares at Sep. 30, 2020

20,036,434

Balances at Dec. 31, 2020

^[3]

200,314

^[4]

$ 3

1,304

292,348

(2)

(93,339)

Balances, shares at Dec. 31, 2020

^[3]

29,831,125

Initial public offering net of issuance costs of $22,870

264,516

$ 1

264,515

Initial public offering net of issuance costs, shares

13,685,000

Equity-based compensation

3,508

3,503

(58)

Balances at Mar. 31, 2021

1,419

1,489

(70)

469,699

$ 4

2,798

560,366

(60)

(93,409)

Balances, shares at Mar. 31, 2021

43,516,125

Balances at Dec. 31, 2020

^[3]

200,314

^[4]

$ 3

1,304

292,348

(2)

(93,339)

Balances, shares at Dec. 31, 2020

^[3]

29,831,125

Balances at Sep. 30, 2021

(33,279)

445,474

$ 4

2,088

569,835

(58)

(126,395)

Balances, shares at Sep. 30, 2021

43,660,909

Balances at Mar. 31, 2021

469,699

$ 4

2,798

560,366

(60)

(93,409)

Balances, shares at Mar. 31, 2021

43,516,125

Issuance of subsidiary common stock

Issuance of subsidiary preferred stock

923

Issuance of common stock under employee stock purchase plan

180

Issuance of common stock under employee stock purchase plan, shares

10,099

Equity-based compensation

4,165

4,159

(55)

Balances at Jun. 30, 2021

(16,439)

(803)

(15,636)

458,540

$ 4

2,991

564,705

(115)

(109,045)

Balances, shares at Jun. 30, 2021

43,526,224

Equity-based compensation

4,557

4,551

Stock option exercises

579

Stock option exercises ,shares

134,685

Balances at Sep. 30, 2021

(18,259)

(909)

(17,350)

$ 445,474

$ 4

$ 2,088

$ 569,835

$ (58)

$ (126,395)

Balances, shares at Sep. 30, 2021

43,660,909

[1]	The consolidated balance sheet as of December 31, 2019 is derived from the audited consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. Changes in stockholders’ equity for the three months ended March 31, 2020, June 30, 2020 and September 30, 2020 were also retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[3]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[4]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Stockholders Equity [Abstract]
Common stock equivalents, net of issuance costs		$ 213
Initial public offering, net of issuance costs	$ 22,870

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
$ in Thousands

9 Months Ended

Sep. 30, 2021

Sep. 30, 2020

Operating activities:

Net loss

$ (33,279)

$ (30,352)

^[1]

Adjustments to reconcile net loss to net cash used in operating activities:

Depreciation and amortization

Equity-based compensation expense

12,230

Amortization or accretion on marketable securities

1,973

146

License expense in exchange for subsidiary common stock

1,019

Acquired in-process research and development assets

6,447

Changes in operating assets and liabilities:

Prepaid expenses and other current assets

(5,104)

(526)

Other assets

Accounts payable

(5,980)

1,064

Accrued expenses and other current liabilities

1,790

1,771

Net cash used in operating activities

(28,262)

(20,336)

Investing activities:

Purchases of property and equipment

(11)

Net cash acquired upon consolidation of Mica

1,450

Purchase of marketable securities

(448,551)

(48,264)

Proceeds from sales and maturities of marketable securities

130,638

29,965

Net cash used in investing activities

(317,913)

(16,860)

Financing activities:

Proceeds from issuance of common stock equivalents

^[2]

14,250

Proceeds from initial public offering

267,268

Payment of issuance costs related to common stock equivalents

^[2]

(213)

Payment of deferred offering costs

(2,688)

Proceeds from issuance of noncontrolling interests

923

1,206

Proceeds from exercise of stock options

579

Net cash provided by financing activities

266,082

15,243

Net decrease in cash and cash equivalents

(80,093)

(21,953)

Cash and cash equivalents at beginning of period

168,198

63,250

Cash and cash equivalents at end of period

88,105

$ 41,297

Noncash financing activities

Deferred offering costs paid in the prior year

$ 65

[1]	The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	Changes in equity activities for the nine months ended September 30, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

Nature of Business and Basis of Presentation

9 Months Ended

Sep. 30, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Basis of Presentation

(1)	Nature of Business and Basis of Presentation

Organization

Cullinan Oncology, Inc., together with its consolidated subsidiaries (Cullinan or the Company), is a biopharmaceutical company developing a diversified pipeline of targeted oncology and immuno-oncology therapies for cancer patients. Cullinan’s predecessor company, Cullinan Pharmaceuticals, LLC was formed in September 2016 and was subsequently renamed Cullinan Oncology, LLC (the LLC) in November 2017. The LLC’s wholly-owned subsidiary, Cullinan Management, Inc. (Management), was formed in September 2016 and became the surviving entity in a reverse merger with the LLC in January 2021. In February 2021, the Company changed its name from Cullinan Management, Inc. to Cullinan Oncology, Inc.

As of December 31, 2020, the Corporation had five development subsidiaries: Cullinan Amber Corp. (Amber), Cullinan Apollo Corp. (Apollo), Cullinan Florentine Corp. (Florentine), Cullinan MICA Corp. (MICA) and Cullinan Pearl Corp. (Pearl). As of September 30, 2021, the Corporation had four development subsidiaries: Amber, Florentine, MICA and Pearl. Apollo was dissolved in August 2021.

Reorganization, Reverse Stock Split and Initial Public Offering

In January 2021, the Company completed its initial public offering (IPO) in which it issued and sold 13,685,000 shares of its common stock, including 1,785,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $21.00 per share. The shares began trading on the Nasdaq Global Select Market on January 8, 2021 under the symbol “CGEM”. The net proceeds received by the Company from the offering were $264.5 million, after deducting underwriting discounts, commissions and other offering expenses.

Immediately prior to the effectiveness of the Company’s registration statement, the Company completed its reorganization, whereby the LLC merged with and into Management and Management was the surviving entity (the Reorganization). Management was the registrant in the IPO. Pursuant to the Reorganization, all outstanding Redeemable Preferred Units, Non-Voting Incentive Units and common units converted into shares of Management common stock while common unit options were exchanged for stock options. Immediately following the Reorganization, the Company effected a one-for-7.0390 reverse stock split of its issued and outstanding shares of common stock (the Reverse Stock Split).

Accordingly, all share and per share amounts for all periods presented in the accompanying unaudited consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and Reverse Stock Split.

Liquidity

The Company has incurred operating losses and negative cash flows from operations since its inception and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities as well as the ability to commercialize the Company’s product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding for the ongoing and planned clinical development of its product candidates. Due to the numerous risks and uncertainties associated with pharmaceutical products and development, the Company is unable to accurately predict the timing or amount of funds required to complete development of its product candidates, and costs could exceed the Company’s expectations for a number of reasons, including reasons beyond the Company’s control. The Company has incurred losses since inception and has an accumulated deficit of $126.4 million as of September 30, 2021.

Since inception, the Company has funded its operations primarily through the sale of equity securities. The Company expects that its cash, cash equivalents, short-term investments and long-term investments as of September 30, 2021 of $445.4 million, will be sufficient to fund its operating expenses and capital expenditure requirements through at least the next twelve months from the date of issuance of these unaudited consolidated financial statements.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

(2)	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP) and in accordance with applicable rules and regulations of the United States Securities and Exchange Commission (SEC) for interim financial reporting. The unaudited consolidated financial statements include accounts of the Company and its consolidated subsidiaries. All intercompany balances have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASUs) of the Financial Accounting Standards Board (FASB).

The unaudited consolidated financial statements have been prepared on the same basis as the annual financial statements and in the opinion of the Company's management, reflect all adjustments, consisting of normal and recurring adjustments, considered necessary for a fair statement of the Company’s financial position, its results of operations and comprehensive loss and its cash flows for the periods presented.

The unaudited consolidated financial statements herein do not include all of the disclosures required by GAAP for a complete set of annual audited financial statements, as is permitted by such rules and regulations. The accompanying financial information should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company's Annual Report on Form 10-K filed with the SEC on March 30, 2021 for the year ended December 31, 2020 (the 2020 Form 10-K).

Use of Estimates

The preparation of the accompanying unaudited consolidated financial statements in accordance with GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosure of contingent assets and liabilities. On an ongoing basis, the Company’s management evaluates the estimates, including those related to expenses and accruals. The Company’s management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Estimates and assumptions reflected in these unaudited consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreements, accrued research and development costs, the valuation of acquired in-process research and development asset and the fair value of equity awards issued by the Company and its subsidiaries prior to the IPO. Actual results may differ from these estimates under different assumptions or conditions.

Principles of Consolidation

The Company consolidates entities in which it has a controlling financial interest. The Company evaluates each of its subsidiaries to determine whether the entity represents a variable interest entity (VIE) for which consolidation should be evaluated under the VIE model, or alternatively, if the entity is a voting interest entity, for which consolidation should be evaluated using the voting interest model (VOE). The Company concluded that none of its subsidiaries is a VIE and has consolidated each subsidiary under the VOE.

The Company has either created or made investments in the following entities:

Consolidated Entities	Relationship as of September 30, 2021	Date Control First Acquired
Cullinan Amber Corp.	Partially-owned Subsidiary	December 2019
Cullinan Florentine Corp.	Partially-owned Subsidiary	December 2019
Cullinan MICA Corp.	Partially-owned Subsidiary	May 2020
Cullinan Pearl Corp.	Partially-owned Subsidiary	November 2018

Noncontrolling Interests

To the extent that ownership interests in the subsidiaries are held by entities other than the Company, management reports these as noncontrolling interests on the consolidated balance sheets. Earnings or losses are attributed to noncontrolling interests under the hypothetical liquidation at book value (HLBV) method. The HLBV method is a point in time calculation that utilizes inputs to determine the amount that the Company and the noncontrolling interest holders would receive upon a hypothetical liquidation at each balance sheet date based on the liquidation provisions of the respective articles of incorporation. At September 30, 2020, investors and licensors held noncontrolling interests in Amber, Apollo, Florentine, MICA and Pearl. At September 30, 2021, investors and licensors held noncontrolling interests in Amber, Florentine, MICA and Pearl. Refer to Note 5 for details relating to the license agreements and Note 7 for details relating to the noncontrolling interests.

For the three and nine months ended September 30, 2020, $1.5 million and $6.9 million of net loss, respectively, were attributable to noncontrolling interests and recorded in the consolidated statements of operations and comprehensive loss and disclosed within the noncontrolling interests in subsidiaries column in the consolidated statements of stockholders’ equity. For the three and nine months ended September 30, 2021, $0.9 million and $0.2 million of net loss, respectively, were attributable to noncontrolling interests and recorded in the consolidated statements of operations and comprehensive loss and disclosed within the noncontrolling interests in subsidiaries column in the consolidated statements of stockholders’ equity.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. As of December 31, 2020 and September 30, 2021, cash equivalents consist of commercial paper and government-backed money market funds.

Investments

The Company determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company periodically reviews its investments in debt securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. If losses on these securities are considered to be other than temporary, the loss is recognized in earnings.

Investments not classified as cash equivalents with maturities of less than twelve months are classified as short-term investments. Investments with maturities greater than twelve months for which the Company has the intent and ability to hold the investment for greater than twelve months are classified as long-term investments in the consolidated balance sheets.

Available-for-sale marketable securities are carried at estimated fair value, with unrealized gains or losses included in accumulated other comprehensive income (loss) in stockholders’ equity. The fair value of marketable securities is based on available market information. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in interest income. Interest and dividends are also included in interest income. Declines in fair value judged to be other-than-temporary on available-for-sale securities, if any, are included in other income (expense), net.

The Company recognized its short-term investments by security type at December 31, 2020:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Corporate notes	$	12,780	$	—	$	(3	)	$	12,777
Commercial paper		24,473		—		—			24,473
Asset-backed securities		4,757		1		—			4,758
Total investments	$	42,010	$	1	$	(3	)	$	42,008

The Company recognized its short-term and long-term investments by security type at September 30, 2021:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Short-term investments
Corporate notes	$	92,049	$	6	$	—		$	92,055
Commercial paper		136,867		16		—			136,883
US government notes		4,001		—		—			4,001
Total short-term investments		232,917		22		—			232,939
Long-term investments
Corporate notes		100,193		—		(77	)		100,116
Asset-backed securities		999		—		—			999
US government notes		23,218		—		(3	)		23,215
Total long-term investments		124,410		—		(80	)		124,330
Total investments	$	357,327	$	22	$	(80	)	$	357,269

Fair Value of Financial Instruments

The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	22,007	$	—	$	—	$	22,007
Money market funds		146,191		—		—		146,191
Total cash and cash equivalents		168,198		—		—		168,198
Short-term investments
Corporate notes		—		12,777		—		12,777
Commercial paper		—		24,473		—		24,473
Asset-backed securities		—		4,758		—		4,758
Total short-term investments		—		42,008		—		42,008
Total cash, cash equivalents and investments	$	168,198	$	42,008	$	—	$	210,206

The following table sets forth the fair value of the Company’s financial assets as of September 30, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	49,111	$	—	$	—	$	49,111
Money market funds		38,994		—		—		38,994
Total cash and cash equivalents		88,105		—		—		88,105
Short-term investments
Corporate notes		—		92,055		—		92,055
Commercial paper		—		136,883		—		136,883
US government notes		—		4,001		—		4,001
Total short-term investments		—		232,939		—		232,939
Long-term investments
Corporate notes		—		100,116		—		100,116
Asset-backed securities		—		999		—		999
US government notes		—		23,215		—		23,215
Total long-term investments		—		124,330		—		124,330
Total cash, cash equivalents and investments	$	88,105	$	357,269	$	—	$	445,374

Prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities are carried at cost, which management believes approximates fair value due to their short-term nature.

Deferred Offering Costs

The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated, at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. The Company incurred $2.7 million of deferred offering costs and recorded such amounts against the gross proceeds of the Company’s IPO within the statements of stockholders’ equity during the nine months ended September 30, 2021.

Asset Acquisitions

The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transactions costs. Goodwill is not recognized in asset acquisitions. In an asset acquisition, the cost allocated to acquire in-process research and development (IPR&D) with no alternative future use is charged to research and development expense at the acquisition date.

Revenue Recognition

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers, or ASC 606. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

The Company enters into licensing arrangements for research and development, manufacturing and commercialization activities, which have components within the scope of ASC 606. Payments pursuant to these arrangements typically include non-refundable, upfront payments, milestone payments upon achieving significant development events, research and development reimbursements, sales milestones and royalties on future product sales. The amount of variable consideration is constrained until it is probable that the revenue is not at a significant risk of reversal in a future period. The contracts into which the Company enters generally do not include significant financing components. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above; b) the transaction price under step (iii) above; c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above, and d) the measure of progress in step (v) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below.

Non-Exclusive Licenses

If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other elements, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining elements, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods.

Milestone Payments

At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

Royalties

For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license of intellectual property is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

Research and Development Costs

Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third-party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs.

Costs incurred to obtain licenses are recognized as research and development expense as incurred if the technology licensed has no alternative future use. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are received or services are performed.

The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. To date, there have been no material differences between the Company’s accrued costs and actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the consolidated statements of operations and comprehensive loss.

Equity-based Compensation

Equity-based compensation is measured at the grant date for all equity-based awards made to employees and non-employees based on the fair value of the awards and is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Company has elected to recognize the actual forfeitures by reducing the equity-based compensation expense in the same period as the forfeitures occur.

The Company estimated the fair value of the stock options using the Black-Scholes option pricing model, which requires the input of objective and subjective assumptions. Certain assumptions used, including the fair value of the Company’s common stock prior to the time of the IPO and stock price volatility, represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, equity-based compensation expense could be materially different for future awards.

The Company classifies equity-based compensation in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Income Taxes

Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A reduction in the carrying value of the deferred tax assets is required when it is not more likely than not that such deferred tax assets are not realizable.

Net Loss per Share

Basic and diluted net loss per share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period, without consideration for potential dilutive shares of common stock, such as stock options, unvested restricted stock awards and shares issuable under the employee stock purchase plan. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted net loss per share are the same for the periods presented. The Company excluded unvested shares of restricted stock awards, stock options and shares issuable under the employee stock purchase plan from the computation of diluted weighted-average shares outstanding as they would be antidilutive.

Recently Issued Accounting Pronouncements Not Yet Adopted

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), to increase transparency and comparability among organizations by recognizing a right-of-use asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either operating or financing, with such classifications affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for fiscal years beginning after December 15, 2019, and early adoption is permitted. ASU 2016-02 was recently delayed for emerging growth companies that elected to adopt new accounting standards on the adoption date required for private companies and will be effective for the Company’s annual reporting period beginning on January 1, 2022 and interim periods beginning in the first quarter of 2023. The Company is evaluating the impact ASU 2016-02 will have on its consolidated financial statements and associated disclosures.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective beginning January 1, 2022. The Company does not expect the adoption of ASU 2019-12 to have a material impact on its consolidated financial position and consolidated results of operations upon adoption.

Reorganization and Reverse Stock Split

9 Months Ended

Sep. 30, 2021

Reorganization And Reverse Stock Split [Abstract]

Reorganization and Reverse Stock Split

(3)	Reorganization and Reverse Stock Split

Immediately prior to the completion of the IPO in January 2021, the LLC completed the Reorganization. Prior to the Reorganization, Management was a wholly-owned subsidiary of the LLC. The LLC was also the direct parent company of the Company’s development subsidiaries. Pursuant to the Reorganization, Management acquired all the assets of the LLC, including all of the stock the LLC owned of Amber, Apollo, Florentine, MICA and Pearl (collectively the Asset Subsidiaries), and assumed all of the LLC’s liabilities and obligations.

Following the Reorganization, all of Management’s outstanding preferred stock automatically converted on a one-for-one basis into common stock of Management. The Company then effected the Reverse Stock Split. Immediately prior to completion of the Company’s IPO, the existing units of the LLC were cancelled and the number of shares of common stock exchanged and issued to the LLC’s unitholders in the Reorganization is shown in the below table by unit class, on a split adjusted basis:

Cullinan Oncology, LLC Unit Type	Number of Management's Shares Issued		Adjusted for the Reverse Stock Split
Series C Preferred Units		66,599,045		9,461,414
Series B Preferred Units		63,141,016		8,970,154
Series A1 Preferred Units		50,000,000		7,103,280
Series Seed Preferred Units		16,000,000		2,273,050
Non-Voting Incentive Units		11,896,500		1,689,949
Common Units		34,747,722		4,936,415
Total shares issued		242,384,283		34,434,262

The amount presented for Non-Voting Incentive Units included unvested outstanding Non-Voting Incentive Units that were exchanged for restricted stock of Management. The amount presented for Common Units included the unvested outstanding Restricted Common Units, exchanged for Management’s restricted stock, and issued and unvested Common Unit Options, that were exchanged for Management’s stock options. The unvested awards are subject to the same time-based vesting conditions as the original awards.

The Reorganization was accounted for as a reverse acquisition, where the LLC was determined to be the accounting acquirer and Management to be the legal acquiree, and recapitalization for financial reporting purposes. Accordingly, the historical financial statements of the LLC became the Company’s historical financial statements, including the comparative prior periods. All share and per share amounts in these unaudited consolidated financial statements and related notes have been retroactively adjusted, where applicable, for all periods presented. The shares of the Company’s common stock for periods prior to the Reorganization represent the outstanding units of the LLC recalculated to give effect to the Reorganization and Reverse Stock Split.

All LLC units that were previously reported as Redeemable Preferred Units, or temporary equity, were converted to common stock of the Company upon the execution of the Reorganization and have been reclassified to stockholders’ equity for all periods presented, as if the Reorganization occurred at the beginning of the earliest period presented in the Company’s financial statements for the years ended December 31, 2019 and 2020, and the nine months ended September 30, 2020 as follows:

	As of December 31, 2019
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		83,872			(83,872	)		—
Series C Redeemable Preferred Units		—			—			—
Total Redeemable Preferred Units		137,774			(137,774	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			2			2
Additional paid-in capital	770				137,773			138,543
Accumulated other comprehensive loss		(4	)		—			(4	)
Accumulated deficit		(41,540	)		—			(41,540	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(40,773	)		137,774			97,001
Non-controlling interests in subsidiaries	864				—			864
Total Stockholders' Equity (Members' Deficit)	$	(39,909	)	$	137,774		$	97,865

	As of September 30, 2020
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		97,909			(97,909	)		—
Total Redeemable Preferred Units		151,811			(151,811	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			2			2
Additional paid-in capital		770			151,810			152,580
Accumulated other comprehensive loss		59			—			59
Accumulated deficit		(64,993	)		—			(64,993	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(64,163	)		151,811			87,648
Non-controlling interests in subsidiaries		1,863			—			1,863
Total Stockholders' Equity (Members' Deficit)	$	(62,300	)	$	151,811		$	89,511

	As of December 31, 2020
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		97,909			(97,909	)		—
Series C Redeemable Preferred Units		124,841			(124,841	)		—
Total Redeemable Preferred Units		276,652			(276,652	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			3			3
Additional paid-in capital		15,698			276,650			292,348
Accumulated other comprehensive loss		(2	)		—			(2	)
Accumulated deficit		(93,339	)		—			(93,339	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(77,642	)		276,652			199,010
Non-controlling interests in subsidiaries		1,304			—			1,304
Total Stockholders' Equity (Members' Deficit)	$	(76,338	)	$	276,652		$	200,314

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2021

Accrued Expenses And Other Current Liabilities [Abstract]

Accrued Expenses and Other Current Liabilities

(4)	Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following:

	December 31, 2020		September 30, 2021
	(in thousands)
Accrued bonus	$	1,763	$	1,764
Professional fees		1,018		755
Research and development costs		1,829		3,223
Other		31		97
	$	4,641	$	5,839

License and Collaboration Agreements

9 Months Ended

Sep. 30, 2021

License And Collaboration Agreements [Abstract]

License and Collaboration Agreements

(5)	License and Collaboration Agreements

The following table summarizes the impact of the research and development costs related to the collaboration and license agreements on the Company’s consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2020 and 2021. For details on the structure and accounting treatment for the Company’s collaboration and license agreements, refer to the annual consolidated financial statements and notes contained in the 2020 Form 10-K.

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2021		2020		2021
	(in thousands)				(in thousands)
Cullinan Oncology - Adimab	$	—	$	46	$	318	$	46
Amber - MIT		—		—		276		71
Apollo - Wistar		—		—		304		—
Florentine - Tubingen		912		—		912		—
Pearl - Taiho		531		—		531		3,000
	$	1,443	$	46	$	2,341	$	3,117

Pearl—Zai Lab License Agreement

In December 2020, Pearl entered into a license agreement (Zai License Agreement) with Zai Lab Shanghai Company, Limited (Zai Lab), to grant Zai Lab an exclusive royalty-bearing license to research, develop, commercialize and manufacture CLN-081 and products which contain CLN-081 in China, Hong Kong, Macau and Taiwan. Zai Lab will be primarily responsible for substantially all the costs related to the operations and control over the significant activities related to the exploitation of the licensed IP of CLN-081.

As partial consideration of the license and rights granted to Zai Lab, Zai Lab paid Pearl a one-time, irrevocable, nonrefundable license fee of $20.0 million in January 2021. In addition to the upfront fee, Zai Lab will be obligated to pay Pearl research and development, regulatory and sales milestone payments upon the occurrence of certain milestone events in the aggregate amount of up to $211.0 million, and tiered royalty payments based on the annual net sales of the licensed product. The Company recognized the upfront license fee in revenue. The Company will also recognize milestone and royalty payments in revenue once they are earned. No milestones have been achieved to date under the Zai License Agreement.

The upfront payment received by Pearl was subject to foreign tax withholdings. When the licensed IP and technology know-how was transferred to Zai Lab in January 2021, Pearl recognized revenue of $18.9 million, which represented the upfront fee less the foreign tax withholdings as Pearl does not expect to recover the amounts relating to the foreign tax withholdings.

In February 2019, Pearl entered into a licensing and collaboration agreement (Taiho License Agreement) with Taiho Pharmaceutical, Co., Ltd. (Taiho Pharma) for the worldwide rights to CLN-081 outside of Japan. In connection with the Taiho License Agreement, Pearl is obligated to pay Taiho Pharma a percentage of future revenue received from Zai Lab, including the upfront payment that was received in January 2021. Upon receipt of the upfront payment, Pearl recognized $3.0 million within research and development expenses in the consolidated statements of operations and comprehensive loss.

Cullinan-MICA Asset Acquisition

9 Months Ended

Sep. 30, 2021

Asset Acquisition [Abstract]

Cullinan-MICA Asset Acquisition

(6)	Cullinan-MICA Asset Acquisition

On May 28, 2020 (the Acquisition Date), in accordance with the Series A Senior Preferred Stock Purchase Agreement (the Purchase Agreement), the Company purchased 5,385,787 shares of Series A Senior Preferred Stock (the Series A Senior Preferred Stock) of PDI Therapeutics, Inc. (PDI Therapeutics), for $7.1 million, and certain existing PDI Therapeutics shareholders purchased approximately 702,495 shares of the Series A Senior Preferred Stock for $0.9 million. Concurrently with the Series A Senior Preferred Stock purchase, PDI Therapeutics was renamed Cullinan MICA Corp. The terms of the Purchase Agreement included two additional closings for total proceeds of up to $26.0 million.

On the Acquisition Date, PDI Therapeutics authorized the issuance of 72,890,797 shares, of which 39,000,000 was designated as common stock and 33,890,797 was designated as preferred stock. Of the authorized preferred stock, PDI Therapeutics designated 1,999,998 shares as Series A Junior Preferred Stock, 652,371 shares as Series A-1 Junior Preferred Stock, 11,451,514 shares as Series A-2 Junior Preferred Stock, and 19,786,914 as Series A Senior Preferred Stock (collectively the Series Preferred Stock). Following the initial close in May 2020, MICA (formerly PDI Therapeutics) had 22,829,406 shares outstanding, including 6,088,282 shares of Series A Senior Preferred Stock (of which the LLC held 5,385,787 shares), 602,784 shares of common stock, and 14,103,883 shares of Series A, A-1 and A2 Junior Preferred Stock described above. In addition, there were 2,034,457 shares of common stock underlying options reserved under MICA’s equity plan (of which 1,826,402 was reserved for future issuances to MICA’s directors and officers, as well as former employees of PDI Therapeutics).

Other than the Series A-1 Junior Preferred Stock, which shares are non-voting, the Series Preferred Stock vote equally with the shares of Common Stock. In addition to any other vote or consent, the vote or written consent of a majority of the holders of Series A Senior Preferred Stock is required for certain actions, including redemptions, dividends, distributions, dissolutions, creation of new classes of stock, mergers, sale of MICA or its assets, and amendments to the certificate of incorporation, as well as other actions. The other classes of Series Preferred Stock have voting rights pertaining to the increase or decrease in the authorized number of shares of their respective classes.

The Company’s initial purchase represented approximately 24% of MICA’s fully-diluted shares outstanding, including shares reserved for future issuance, and 88.5% of the Series A Senior Preferred Stock outstanding. The Company can increase its ownership to approximately 54% of MICA’s fully-diluted shares outstanding with the subsequent closings. Additionally, as part of the transaction and as outlined in the Voting Agreement dated May 28, 2020, among the Company and other stockholders of MICA, MICA increased the size of its board of directors from four to five directors, of which three directors are designated by the Company.

The Company also entered into a Services Agreement with MICA under which the Company will perform functions required for MICA’s operations, including accounts payable, cash management, record keeping, research and development and accounting services.

Given the Company’s ownership of the Series A Senior Preferred Stock and its majority representation on MICA’s board of directors, the Company’s obtained a controlling interest in MICA on the Acquisition Date. Further, the Company evaluated the MICA transaction and determined that MICA is not a variable interest entity; however, due to the controlling interest in MICA, the Company will consolidate MICA under the voting interest model.

The Company evaluated the change in control of MICA and concluded that the change in control was an asset acquisition rather than a business combination as substantially all of the value in MICA resided in CLN-619, the in-process research and development (IPR&D) asset developed by MICA. The cost of the assets was calculated as the sum of the fair value of the Company’s investment in MICA, the fair value of the noncontrolling interests in MICA and the Company’s transaction costs. This cost was allocated to the assets acquired and liabilities assumed in the transaction based on their relative fair values. The amount allocated to the IPR&D asset acquired was $6.4 million and was charged to research and development expense within the consolidated statements of operations and comprehensive loss during the nine months ended September 30, 2020 as it had no alternative future use at the time of the acquisition.

In December 2020, the stockholders and the board of directors of MICA approved an amendment to its equity plan that decreased the authorized amount of shares under its equity plan such that no further grants could be made under its equity plan. Any authorized but unissued shares under the equity plan were returned to the status of authorized, unissued shares of common stock.

In June 2021, the MICA board authorized the first additional closing and the Company purchased an additional 5,385,787 shares of Series A Senior Preferred Stock for $7.1 million and certain existing shareholders purchased an additional 702,495 shares of Series A Senior Preferred Stock for $0.9 million pursuant to the Purchase Agreement. Following the first additional closing, the Company’s ownership increased to 45% of MICA’s fully-diluted shares outstanding.

Common Stock and Noncontrolling Interest in Subsidiaries

9 Months Ended

Sep. 30, 2021

Common Stock And Noncontrolling Interest In Subsidiaries [Abstract]

Common Stock and Noncontrolling Interest in Subsidiaries

(7)	Common Stock and Noncontrolling Interest in Subsidiaries

Common Stock

As of December 31, 2020 and September 30, 2021, 34,900,878 and 150,000,000 shares of common stock of the Company were authorized, respectively. Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company. No dividends have been declared through September 30, 2021.

The LLC’s outstanding Non-Voting Incentive Units have been retroactively adjusted to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and Reverse Stock Split.

Noncontrolling Interest in Subsidiaries

Certain subsidiaries issue common stock in connection with licensing agreements and to employees, directors and consultants pursuant to subsidiary equity incentive plans. The holders of subsidiary common stock are entitled to one vote per share. The holders of subsidiary common stock are entitled to receive dividends when and if declared by the subsidiaries’ board of directors and distributions in either case only after the payment of all preferential amounts required to be paid to the holders of shares of Series A Preferred Stock of the respective subsidiary.

In November 2020, the LLC entered into a Restricted Stock Contribution Agreement (Contribution Agreement) with Amber, Pearl and Florentine where the LLC exchanged common units of the LLC for restricted common stock held by LLC employees at each of the subsidiaries. The LLC’s outstanding restricted common units have been retroactively adjusted to reflect the effect of the Reorganization and Reverse Stock Split. Refer to Note 3 for additional details relating to the Reorganization and the Reverse Stock Split.

Cullinan Amber Corp.

In April 2020, in connection with its Series A Preferred Stock financing, Amber issued 3,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $3.0 million. At any time following the initial closing, upon election of Amber’s board of directors, Amber may sell up to an aggregate of 9,000,000 shares of Amber’s Series A Preferred Stock at one or more subsequent closings at $1.00 per share.

In April 2020, pursuant to the license agreement (MIT License Agreement) between Amber and the Massachusetts Institute of Technology (MIT), Amber issued 400,132 shares of its common stock, in exchange for no additional consideration as set forth in the MIT License Agreement.

In June 2021, upon election by Amber’s board of directors, Amber issued an additional 3,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $3.0 million. In connection with the financing, Amber issued 153,229 shares of its common stock to MIT in exchange for no additional consideration, as set forth in the MIT License Agreement.

Under the HLBV method, $0.2 million of losses were attributed to the noncontrolling interests for each of the three and nine months ended September 30, 2020. Under the HLBV method, the Company did not attribute any losses to the noncontrolling interests for the three months ended September 30, 2021 and less than $0.1 million of losses were attributed to noncontrolling interests for the nine months ended September 30, 2021.

Cullinan Apollo Corp.

In December 2018, Apollo entered into a Series A Preferred Stock purchase agreement with the Company. The initial closing took place in December and Apollo sold 7,000,000 subsidiary shares of Series A Preferred Stock for gross proceeds of $7.0 million. Pursuant to the Series A Preferred Stock purchase agreement, at any time following the initial closing, upon the election of Apollo’s board of directors, Apollo could sell up to an aggregate of 11,000,000 Series A Preferred Stock shares at one or more subsequent closings at $1.00 per share.

The Company dissolved Apollo in August 2021. The Company did not allocate any losses to the noncontrolling interests for each of the three and nine months ended September 30, 2020 and 2021.

Cullinan Florentine Corp.

In August 2020, Florentine entered into a Series A Preferred Stock purchase agreement with the Company. The initial closing took place in August 2020 and Florentine sold 6,000,000 shares of its Series A Preferred Stock to the Company for gross proceeds of $6.0 million. At any time following the initial closing, upon the election of the Florentine’s board of directors, Florentine may sell up to an additional 6,000,000 shares of Series A Preferred Stock at one or more subsequent closings at $1.00 per share. Pursuant to the license agreement (Tübingen License Agreement) Florentine entered into with Deutsches Krebsforschungszentrum (DKFZ), Eberhard Karls University of Tübingen, Faculty of Medicine (University of Tübingen), and Universitätsmedizin Gesellschaft für Forschung und Entwicklung mbH, Tübingen (UFE), Florentine issued 725,118 shares of its common stock, in exchange for no additional consideration as set forth in the Tübingen License Agreement.

In December 2020, Florentine issued 6,000,000 additional shares of its Series A Preferred Stock to the Company for proceeds of $6.0 million under the Florentine Series A Preferred Stock purchase agreement. Florentine issued an additional 381,810 shares of its common stock to DFKZ and UFE as anti-dilution shares, in exchange for no additional consideration as set forth in the Tübingen License Agreement.

In July 2021, Florentine issued 7,500,000 shares of Series B Preferred Stock to the Company for gross proceeds of $8.1 million under the Florentine Series B Preferred Stock purchase agreement. No additional shares of its stock were issued to DFKZ or UFE.

Under the HLBV method, $0.3 million of losses were attributed to noncontrolling interests for each of the three and nine months ended September 30, 2020. The Company did not allocate any losses to the noncontrolling interests for each of the three and nine months ended September 30, 2021.

Cullinan MICA Corp.

In May 2020, MICA issued 6,088,282 million shares of Series A Senior Preferred Stock, including 5,385,787 shares to the Company, at $1.31 per share. See Note 6 for further details.

Using a market-based approach and an option-pricing allocation method, MICA determined the fair market value of MICA’s equity at acquisition was $12.8 million, of which $7.1 million was allocated to the Company’s Series A Senior Preferred Stock position, and $5.7 million was initially allocated to noncontrolling interests, including the Junior Preferred and Common Stockholders.

In December 2020, the MICA board authorized the issuance of 3,367,804 shares of MICA common stock to the Company, at a purchase price of $0.23 per share for aggregate proceeds to MICA of $0.8 million. As a result of these transactions, the Company’s ownership interests in MICA increased to 35% as of December 31, 2020.

In June 2021, pursuant the first additional closing as described in Note 6, the Company’s ownership interests in MICA increased to 45%.

Under the HLBV method, less than $0.1 million and $5.1 million of losses were attributed to noncontrolling interests for the three and nine months ended September 30, 2020, respectively. Under the HLBV method, $0.3 million and $0.8 million of losses were attributed to noncontrolling interests for the three and nine months ended September 30, 2021, respectively.

Cullinan Pearl Corp.

In February 2019, Pearl entered into a Series A Preferred Stock Purchase Agreement with the Company and Taiho Ventures, LLC (Taiho Ventures) to sell up to 23,000,000 shares of Pearl’s Series A Preferred Stock for $1.00 per share. Pearl completed the initial closing of its Series A Preferred Stock where Pearl issued 14,000,000 shares of Series A Preferred Stock for $14.0 million to the Company and Taiho Ventures. In connection with the Taiho License Agreement, Pearl issued 1,860,000 shares of common stock to Taiho Ventures as anti-dilution shares, in exchange for no cash consideration.

In August 2020, Pearl issued 9,000,000 additional shares of its Series A Preferred Stock for $9.0 million to the Company and Taiho Ventures. In connection with the Taiho License Agreement, Pearl then issued 1,206,000 to Taiho Ventures additional shares of its common stock as anti-dilution shares, in exchange for no additional consideration.

In November 2020, pursuant a subscription agreement between the Company and Pearl, the Company purchased 2,730,227 shares of Pearl’s common stock at $0.44 per share, for an aggregate purchase price of $1.2 million.

Under the HLBV method, $0.9 million and $1.3 million of losses were attributed to noncontrolling interests for the three and nine months ended September 30, 2020, respectively. Under the HLBV method, $0.6 million of losses and $0.7 million of income were attributed to noncontrolling interests for the three and nine months ended September 30, 2021, respectively.

Equity-Based Compensation

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity-Based Compensation

(8)	Equity-Based Compensation

2021 Stock Options and Incentive Plan

The Company’s 2021 Stock Option and Incentive Plan (the 2021 Stock Plan) was adopted by the board of directors in December 2020 and the stockholders approved the plan in January 2021, prior to the completion of the Company’s IPO. The 2021 Stock Plan became effective on the day immediately prior to the effectiveness of the Company’s registration statement. The 2020 Unit Option and Grant Plan was terminated once the 2021 Stock Plan was effective. The Company initially reserved 12,546,386 shares of common stock for issuance of awards under the 2021 Stock Plan, which included (x) split-adjusted 320,228 shares of restricted stock issued under the 2021 Stock Plan in connection with the Reorganization and (y) split-adjusted equity awards comprised of (i) 4,616,187 shares of common stock issuable upon the exercise of stock options at a weighted average exercise price of $4.30; and (ii) an aggregate of 1,753,316 shares of common stock issuable upon the exercise of the stock options, with an exercise price equal to the IPO price per share, which were granted to certain executive officers, employees, and affiliates.

The 2021 Stock Plan provides that the number of shares reserved and available for issuance under the 2021 Stock Plan will automatically increase each January 1, beginning on January 1, 2022, by 5% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s board or compensation committee. This number is subject to adjustment in the event of a stock split, stock dividend or other change in capitalization.

The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive loss:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2021		2020		2021
	(in thousands)				(in thousands)
Research and development	$	—	$	2,458	$	—	$	6,320
General and administrative		—		2,099		—		5,910
Total equity-based compensation	$	—	$	4,557	$	—	$	12,230

2021 Employee Stock Purchase Plan

The Company’s 2021 Employee Stock Purchase Plan (the ESPP) was adopted by the board of directors in December 2020 and the stockholders approved the plan in January 2021, prior to the completion of the Company’s IPO. The ESPP became effective on the day immediately prior to the effectiveness of the Company’s IPO. The Company has initially reserved 416,665 shares of common stock for issuance to participating employees.

The ESPP provides that the number of shares reserved and available for issuance under the ESPP will automatically increase each January 1, beginning on January 1, 2022, by the lesser of 833,330 shares of the Company’s common stock, 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. This number is subject to adjustment in the event of a stock split, stock dividend or other change in capitalization.

The Company issued 10,099 shares of its common stock on June 30, 2021 pursuant to the ESPP. The Company recorded less than $0.1 million of equity-based compensation expense relating to the ESPP for each of the three and nine months ended September 30, 2021.

Related Party Transactions

9 Months Ended

Sep. 30, 2021

Related Party Transactions

(9)	Related Party Transactions

In April 2020, the Company entered into a consulting agreement (the 2020 Consulting Agreement) with Globeways Holdings Limited, or Globeways. Globeways and entities affiliated with F2 Ventures beneficially own in the aggregate greater than five percent of the Company’s outstanding units and Globeways is beneficially owned by a member of the Company’s board of directors. Pursuant to the 2020 Consulting Agreement, the board member provides leadership and advice regarding the Company’s scientific, clinical, product development and related activities and operations. Pursuant to the 2020 Consulting Agreement, the LLC pays Globeways a consulting fee at a monthly rate of $25,000. As the sole beneficial owner of Globeways, this board member receives all of the compensation paid to Globeways under the 2020 Consulting Agreement.

For each of the three months and nine months ended September 30, 2020, the Company incurred less than $0.1 million and $0.2 million in costs related to this agreement, respectively. The Company did not incur any expenses relating to the Globeways Agreement for the three months ended September 30, 2021 as the agreement expired as of March 31, 2021. For the nine months ended September 30, 2021, the Company incurred less than $0.1 million in costs related to the 2020 Consulting Agreement.

Royalty Transfer Agreements

Between October 2019 and May 2020, each of the Asset Subsidiaries entered into royalty transfer agreements with MPM Oncology Charitable Foundation, Inc. and UBS Optimus Foundation (together, the Foundations). Under each of these respective agreements, each Foundation is entitled to receive a royalty equal to 0.5% (1.0% in aggregate) of all global net sales of any products developed by the applicable subsidiary, subject to limitations after patent expirations and on intellectual property developed after a change of control. The Company has deemed these royalty transfer agreements to be freestanding financial instruments that should be accounted for at fair value. Management of the Company has concluded that these instruments had no value at the inception of the agreements and at December 31, 2020 and September 30, 2021.

Given the early-stage nature of the underlying technologies and inherent technical, regulatory and competitive risks associated with achieving approval and commercialization, the Company ascribed no value to the royalty transfer agreements as of December 31, 2020 and September 30, 2021. The Company currently does not have any applicable net sales from its products and as a result, has paid no royalties under these obligation as of December 31, 2020 and September 30, 2021 nor has the Company accrued any liability as of December 31, 2020 and September 30, 2021. The Company will monitor these instruments for changes in fair value at each reporting date.

Income Taxes

9 Months Ended

Sep. 30, 2021

Income Tax Disclosure [Abstract]

Income Taxes

(10)	Income Taxes

The Company recorded no provision for income taxes for each of the three months and nine months ended September 30, 2020 and 2021.

Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax bases of assets and liabilities using statutory rates. Management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards and research and development credits. Under the applicable accounting standards, management has considered the Company’s history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of federal and state deferred tax assets. Accordingly, a full valuation allowance has been established against the Company’s otherwise recognizable net deferred tax assets.

Commitments And Contingencies Disclosure [Abstract]

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Commitments and Contingencies

9 Months Ended

Sep. 30, 2021

Commitments and Contingencies

(11)	Commitments and Contingencies

Operating Lease

Rent expense for the three and nine months ended September 30, 2020 was $0.2 million and $0.4 million, respectively. Rent expense for the three and nine months ended September 30, 2021 was $0.2 million and $0.5 million, respectively.

In December 2017, the Company signed an operating lease for 7,531 rentable square feet of office space in Cambridge, Massachusetts, which commenced on February 1, 2018. The lease expires on June 30, 2024. Rent expense is recorded ratably over the lease period. The lease includes escalating rental payments, which are also being charged to rent expense ratably over the lease period.

The following table summarizes future minimum payments due under the operating lease as of September 30, 2021:

	(in thousands)
Remainder of 2021	$	150
2022		608
2023		618
2024		313
	$	1,689

Employee Benefit Plan

9 Months Ended

Sep. 30, 2021

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plan

(12)	Employee Benefit Plan

The Company maintains a defined contribution 401(k) plan (the 401(k) Plan) in which employees may contribute a portion of their compensation, subject to statutory maximum contribution amounts. The Company assumes all administrative costs of the 401(k) Plan. For each of the three months ended September 30, 2020 and 2021, the expense relating to the matching contribution was less than $0.1 million. For the nine months ended September 30, 2020 and 2021, the expense relating to the matching contribution was less than $0.1 million and $0.2 million, respectively.

Net Loss per Share

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Net Loss per Share

(13)	Net Loss per Share

The following table sets forth the calculation of basic and diluted net loss per share:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2021			2020 ⁽¹⁾			2021
	(in thousands, except share and per share data)						(in thousands, except share and per share data)
Numerator:
Net loss attributable to common stockholders of Cullinan	$	(9,858	)	$	(17,350	)	$	(23,453	)	$	(33,056	)
Denominator
Total weighted-average shares used in computing net loss per share, basic and diluted		19,721,992			43,438,861			19,453,479			43,254,230
Net Loss per Share:	$	(0.50	)	$	(0.40	)	$	(1.21	)	$	(0.76	)

(1) The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the for additional details.

The following outstanding equity instruments were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive:

	As of September 30,
	2020		2021
Restricted stock awards		274,357		131,812
Stock options		—		7,200,268
Estimated shares issuable under the ESPP		—		2,234
Total		274,357		7,334,314

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Principles of Consolidation

The Company has either created or made investments in the following entities:

Consolidated Entities	Relationship as of September 30, 2021	Date Control First Acquired
Cullinan Amber Corp.	Partially-owned Subsidiary	December 2019
Cullinan Florentine Corp.	Partially-owned Subsidiary	December 2019
Cullinan MICA Corp.	Partially-owned Subsidiary	May 2020
Cullinan Pearl Corp.	Partially-owned Subsidiary	November 2018

Noncontrolling Interests

Cash and Cash Equivalents

Investments

The Company recognized its short-term investments by security type at December 31, 2020:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Corporate notes	$	12,780	$	—	$	(3	)	$	12,777
Commercial paper		24,473		—		—			24,473
Asset-backed securities		4,757		1		—			4,758
Total investments	$	42,010	$	1	$	(3	)	$	42,008

The Company recognized its short-term and long-term investments by security type at September 30, 2021:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Short-term investments
Corporate notes	$	92,049	$	6	$	—		$	92,055
Commercial paper		136,867		16		—			136,883
US government notes		4,001		—		—			4,001
Total short-term investments		232,917		22		—			232,939
Long-term investments
Corporate notes		100,193		—		(77	)		100,116
Asset-backed securities		999		—		—			999
US government notes		23,218		—		(3	)		23,215
Total long-term investments		124,410		—		(80	)		124,330
Total investments	$	357,327	$	22	$	(80	)	$	357,269

Fair Value of Financial Instruments

The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	22,007	$	—	$	—	$	22,007
Money market funds		146,191		—		—		146,191
Total cash and cash equivalents		168,198		—		—		168,198
Short-term investments
Corporate notes		—		12,777		—		12,777
Commercial paper		—		24,473		—		24,473
Asset-backed securities		—		4,758		—		4,758
Total short-term investments		—		42,008		—		42,008
Total cash, cash equivalents and investments	$	168,198	$	42,008	$	—	$	210,206

The following table sets forth the fair value of the Company’s financial assets as of September 30, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	49,111	$	—	$	—	$	49,111
Money market funds		38,994		—		—		38,994
Total cash and cash equivalents		88,105		—		—		88,105
Short-term investments
Corporate notes		—		92,055		—		92,055
Commercial paper		—		136,883		—		136,883
US government notes		—		4,001		—		4,001
Total short-term investments		—		232,939		—		232,939
Long-term investments
Corporate notes		—		100,116		—		100,116
Asset-backed securities		—		999		—		999
US government notes		—		23,215		—		23,215
Total long-term investments		—		124,330		—		124,330
Total cash, cash equivalents and investments	$	88,105	$	357,269	$	—	$	445,374

Deferred Offering Costs

Asset Acquisitions

Revenue Recognition

Non-Exclusive Licenses

Milestone Payments

Royalties

Research and Development Costs

Patent Costs

Equity-based Compensation

Income Taxes

Net Loss per Share

Recently Issued Accounting Pronouncements Not Yet Adopted

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Schedule of Short-term and Long-term Investments by Security Type

The Company recognized its short-term investments by security type at December 31, 2020:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Corporate notes	$	12,780	$	—	$	(3	)	$	12,777
Commercial paper		24,473		—		—			24,473
Asset-backed securities		4,757		1		—			4,758
Total investments	$	42,010	$	1	$	(3	)	$	42,008

The Company recognized its short-term and long-term investments by security type at September 30, 2021:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Short-term investments
Corporate notes	$	92,049	$	6	$	—		$	92,055
Commercial paper		136,867		16		—			136,883
US government notes		4,001		—		—			4,001
Total short-term investments		232,917		22		—			232,939
Long-term investments
Corporate notes		100,193		—		(77	)		100,116
Asset-backed securities		999		—		—			999
US government notes		23,218		—		(3	)		23,215
Total long-term investments		124,410		—		(80	)		124,330
Total investments	$	357,327	$	22	$	(80	)	$	357,269

Summary of Fair Value of Financial Assets Measured on Recurring Basis

The following table sets forth the fair value of the Company’s financial assets as of December 31, 2020, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	22,007	$	—	$	—	$	22,007
Money market funds		146,191		—		—		146,191
Total cash and cash equivalents		168,198		—		—		168,198
Short-term investments
Corporate notes		—		12,777		—		12,777
Commercial paper		—		24,473		—		24,473
Asset-backed securities		—		4,758		—		4,758
Total short-term investments		—		42,008		—		42,008
Total cash, cash equivalents and investments	$	168,198	$	42,008	$	—	$	210,206

The following table sets forth the fair value of the Company’s financial assets as of September 30, 2021, allocated into Level 1, Level 2 and Level 3, that was measured on a recurring basis:

	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents
Cash	$	49,111	$	—	$	—	$	49,111
Money market funds		38,994		—		—		38,994
Total cash and cash equivalents		88,105		—		—		88,105
Short-term investments
Corporate notes		—		92,055		—		92,055
Commercial paper		—		136,883		—		136,883
US government notes		—		4,001		—		4,001
Total short-term investments		—		232,939		—		232,939
Long-term investments
Corporate notes		—		100,116		—		100,116
Asset-backed securities		—		999		—		999
US government notes		—		23,215		—		23,215
Total long-term investments		—		124,330		—		124,330
Total cash, cash equivalents and investments	$	88,105	$	357,269	$	—	$	445,374

Reorganization And Reverse Stock Split [Abstract]

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Reorganization and Reverse Stock Split (Tables)

9 Months Ended

Sep. 30, 2021

Number of Shares of Common Stock Exchanged and Issued to Unitholders on Split Adjusted Basis

the existing units of the LLC were cancelled and the number of shares of common stock exchanged and issued to the LLC’s unitholders in the Reorganization is shown in the below table by unit class, on a split adjusted basis:

Cullinan Oncology, LLC Unit Type	Number of Management's Shares Issued		Adjusted for the Reverse Stock Split
Series C Preferred Units		66,599,045		9,461,414
Series B Preferred Units		63,141,016		8,970,154
Series A1 Preferred Units		50,000,000		7,103,280
Series Seed Preferred Units		16,000,000		2,273,050
Non-Voting Incentive Units		11,896,500		1,689,949
Common Units		34,747,722		4,936,415
Total shares issued		242,384,283		34,434,262

Summary of LLC Units Previously Reported as Redeemable Preferred Units or Temporary Equity Converted Reclassified to Equity

	As of December 31, 2019
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		83,872			(83,872	)		—
Series C Redeemable Preferred Units		—			—			—
Total Redeemable Preferred Units		137,774			(137,774	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			2			2
Additional paid-in capital	770				137,773			138,543
Accumulated other comprehensive loss		(4	)		—			(4	)
Accumulated deficit		(41,540	)		—			(41,540	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(40,773	)		137,774			97,001
Non-controlling interests in subsidiaries	864				—			864
Total Stockholders' Equity (Members' Deficit)	$	(39,909	)	$	137,774		$	97,865

	As of September 30, 2020
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		97,909			(97,909	)		—
Total Redeemable Preferred Units		151,811			(151,811	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			2			2
Additional paid-in capital		770			151,810			152,580
Accumulated other comprehensive loss		59			—			59
Accumulated deficit		(64,993	)		—			(64,993	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(64,163	)		151,811			87,648
Non-controlling interests in subsidiaries		1,863			—			1,863
Total Stockholders' Equity (Members' Deficit)	$	(62,300	)	$	151,811		$	89,511

	As of December 31, 2020
	As Reported			Adjustment			As Adjusted
	(in thousands)
Redeemable Preferred Units
Series Seed Redeemable Preferred Units	$	3,956		$	(3,956	)	$	—
Series A1 Redeemable Preferred Units		49,946			(49,946	)		—
Series B Redeemable Preferred Units		97,909			(97,909	)		—
Series C Redeemable Preferred Units		124,841			(124,841	)		—
Total Redeemable Preferred Units		276,652			(276,652	)		—
Stockholders' Equity (Members' Deficit)
Non-Voting Incentive Units	1				(1	)		—
Common Stock		—			3			3
Additional paid-in capital		15,698			276,650			292,348
Accumulated other comprehensive loss		(2	)		—			(2	)
Accumulated deficit		(93,339	)		—			(93,339	)
Total Cullinan Stockholders' Equity (Members' Deficit)		(77,642	)		276,652			199,010
Non-controlling interests in subsidiaries		1,304			—			1,304
Total Stockholders' Equity (Members' Deficit)	$	(76,338	)	$	276,652		$	200,314

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2021

Accrued Expenses And Other Current Liabilities [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following:

	December 31, 2020		September 30, 2021
	(in thousands)
Accrued bonus	$	1,763	$	1,764
Professional fees		1,018		755
Research and development costs		1,829		3,223
Other		31		97
	$	4,641	$	5,839

License and Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2021

License And Collaboration Agreements [Abstract]

Summary of Research and Development Costs Related to Collaboration and License Agreements

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2021		2020		2021
	(in thousands)				(in thousands)
Cullinan Oncology - Adimab	$	—	$	46	$	318	$	46
Amber - MIT		—		—		276		71
Apollo - Wistar		—		—		304		—
Florentine - Tubingen		912		—		912		—
Pearl - Taiho		531		—		531		3,000
	$	1,443	$	46	$	2,341	$	3,117

Equity-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss)

The Company recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive loss:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2021		2020		2021
	(in thousands)				(in thousands)
Research and development	$	—	$	2,458	$	—	$	6,320
General and administrative		—		2,099		—		5,910
Total equity-based compensation	$	—	$	4,557	$	—	$	12,230

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2021

Commitments And Contingencies Disclosure [Abstract]

Summary of Future Minimum Payments Due Under Operating Lease

The following table summarizes future minimum payments due under the operating lease as of September 30, 2021:

	(in thousands)
Remainder of 2021	$	150
2022		608
2023		618
2024		313
	$	1,689

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Summary of Calculation of Basic and Diluted Net Loss Per Share

The following table sets forth the calculation of basic and diluted net loss per share:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2021			2020 ⁽¹⁾			2021
	(in thousands, except share and per share data)						(in thousands, except share and per share data)
Numerator:
Net loss attributable to common stockholders of Cullinan	$	(9,858	)	$	(17,350	)	$	(23,453	)	$	(33,056	)
Denominator
Total weighted-average shares used in computing net loss per share, basic and diluted		19,721,992			43,438,861			19,453,479			43,254,230
Net Loss per Share:	$	(0.50	)	$	(0.40	)	$	(1.21	)	$	(0.76	)

Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Loss Per Share

The following outstanding equity instruments were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive:

	As of September 30,
	2020		2021
Restricted stock awards		274,357		131,812
Stock options		—		7,200,268
Estimated shares issuable under the ESPP		—		2,234
Total		274,357		7,334,314

Nature of Business and Basis of Presentation - Additional Information (Details)
$ / shares in Units, $ in Thousands

1 Months Ended

3 Months Ended

9 Months Ended

Jan. 31, 2021

USD ($)

$ / shares

Sep. 30, 2021

USD ($)

Subsidiary

Jun. 30, 2021

USD ($)

Mar. 31, 2021

USD ($)

Sep. 30, 2020

USD ($)

Jun. 30, 2020

USD ($)

Mar. 31, 2020

USD ($)

Sep. 30, 2021

USD ($)

Subsidiary

Sep. 30, 2020

USD ($)

Dec. 31, 2020

USD ($)

Subsidiary

Dec. 31, 2019

USD ($)

Nature Of Business And Basis Of Presentation [Line Items]

Number of development subsidiaries | Subsidiary

Proceeds from initial public offering

$ 264,500

$ 267,268

Reverse stock split conversion ratio

Reverse stock split

one-for-7.0390

Net Income (loss)

$ 18,259

$ 16,439

$ (1,419)

$ 11,314

$ 13,875

$ 5,163

$ 33,279

$ 30,352

^[1]

Cash, cash equivalents, short-term investments and long-term investments

(126,395)

$ (64,993)

(126,395)

$ (64,993)

$ (93,339)

^[2]

$ (41,540)

$ 445,400

IPO

Nature Of Business And Basis Of Presentation [Line Items]

Common stock shares issued and sold | shares

13,685,000

Stock, price per Share | $ / shares

$ 21.00

Underwriters' Option

Nature Of Business And Basis Of Presentation [Line Items]

Common stock shares issued and sold | shares

1,785,000

[1]	The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Net loss attributable to noncontrolling interests	$ (0.9)	$ (1.5)	$ (0.2)	$ (6.9)
Deferred offering costs	$ 2.7		$ 2.7

Summary of Significant Accounting Policies - Schedule of Short-term and Long-term Investments by Security Type (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 357,327	$ 42,010
Gross Unrealized Gains	22	1
Gross Unrealized Losses	(80)	(3)
Estimated Fair Value	357,269	42,008
Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	124,410
Gross Unrealized Losses	(80)
Estimated Fair Value	124,330
Long Term Investment \| US Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	23,218
Gross Unrealized Losses	(3)
Estimated Fair Value	23,215
Corporate Note Securities \| Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	100,193
Gross Unrealized Losses	(77)
Estimated Fair Value	100,116
Asset-backed Securities \| Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	999
Estimated Fair Value	999
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	232,917
Gross Unrealized Gains	22
Estimated Fair Value	232,939
Short Term Investments \| US Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	4,001
Estimated Fair Value	4,001
Short Term Investments \| Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	92,049	12,780
Gross Unrealized Gains	6
Gross Unrealized Losses		(3)
Estimated Fair Value	92,055	12,777
Short Term Investments \| Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost		4,757
Gross Unrealized Gains		1
Estimated Fair Value		4,758
Short Term Investments \| Commercial Paper
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	136,867	24,473
Gross Unrealized Gains	16
Estimated Fair Value	$ 136,883	$ 24,473

Summary of Significant Accounting Policies - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 88,105	$ 168,198
Total short-term investments	232,939	42,008
Total cash, cash equivalents and investments	445,374	210,206
Total long-term investments	124,330
US Government Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	4,001
Total long-term investments	23,215
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	49,111	22,007
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	38,994	146,191
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	88,105	168,198
Total cash, cash equivalents and investments	88,105	168,198
Level 1 \| Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	49,111	22,007
Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash and cash equivalents	38,994	146,191
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	232,939	42,008
Total cash, cash equivalents and investments	357,269	42,008
Total long-term investments	124,330
Level 2 \| US Government Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	4,001
Total long-term investments	23,215
Corporate Note Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	92,055	12,777
Total long-term investments	100,116
Corporate Note Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	92,055	12,777
Total long-term investments	100,116
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	136,883	24,473
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	136,883	24,473
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		4,758
Total long-term investments	999
Asset-backed Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		$ 4,758
Total long-term investments	$ 999

Reorganization and Reverse Stock Split - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021
Reorganization And Reverse Stock Split [Abstract]
Reverse stock split conversion ratio	1

Reorganization and Reverse Stock Split - Number of Shares of Common Stock Exchanged and Issued to Unitholders on Split Adjusted Basis (Details) - Cullinan Oncology, LLC	9 Months Ended
	Sep. 30, 2021 shares
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	242,384,283
Adjusted for the Reverse Stock Split	34,434,262
Series C Preferred Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	66,599,045
Adjusted for the Reverse Stock Split	9,461,414
Series B Preferred Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	63,141,016
Adjusted for the Reverse Stock Split	8,970,154
Series A1 Preferred Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	50,000,000
Adjusted for the Reverse Stock Split	7,103,280
Series Seed Preferred Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	16,000,000
Adjusted for the Reverse Stock Split	2,273,050
Non-Voting Incentive Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	11,896,500
Adjusted for the Reverse Stock Split	1,689,949
Common Units
Reorganization And Reverse Stock Split [Line Items]
Number of Management's Shares Issued	34,747,722
Adjusted for the Reverse Stock Split	4,936,415

Reorganization and Reverse Stock Split - Summary of LLC Units Previously Reported as Redeemable Preferred Units or Temporary Equity Converted Reclassified to Equity (Details) - USD ($)
$ in Thousands

Sep. 30, 2021

Jun. 30, 2021

Mar. 31, 2021

Dec. 31, 2020

Sep. 30, 2020

Jun. 30, 2020

Mar. 31, 2020

Dec. 31, 2019

Stockholders' Equity (Members' Deficit)

Common Stock

$ 4

$ 3

^[1]

$ 2

Accumulated other comprehensive loss

569,835

292,348

^[1]

152,580

138,543

(58)

(2)

^[1]

(4)

Total Cullinan Stockholders' Equity (Members' Deficit)

(126,395)

(93,339)

^[1]

(64,993)

(41,540)

443,386

199,010

^[1]

87,648

97,001

Non-controlling interests in subsidiaries

2,088

1,304

^[1]

1,863

864

Total Stockholders' Equity (Members' Deficit)

$ 445,474

$ 458,540

$ 469,699

200,314

^[1],[2]

89,511

$ 98,919

$ 106,769

97,865

^[3]

As Reported

Stockholders' Equity (Members' Deficit)

276,652

151,811

137,774

Non-Voting Incentive Units

Accumulated other comprehensive loss

15,698

770

(2)

(4)

Total Cullinan Stockholders' Equity (Members' Deficit)

(93,339)

(64,993)

(41,540)

(77,642)

(64,163)

(40,773)

Non-controlling interests in subsidiaries

1,304

1,863

864

Total Stockholders' Equity (Members' Deficit)

(76,338)

(62,300)

(39,909)

Adjustment

Stockholders' Equity (Members' Deficit)

(276,652)

(151,811)

(137,774)

Non-Voting Incentive Units

(1)

Common Stock

Total Cullinan Stockholders' Equity (Members' Deficit)

276,650

151,810

137,773

276,652

151,811

137,774

Total Stockholders' Equity (Members' Deficit)

276,652

151,811

137,774

Series Seed Redeemable Preferred Units | As Reported

Series Seed Redeemable Preferred Units | Adjustment

3,956

Series A1 Redeemable Preferred Units | As Reported

(3,956)

Series A1 Redeemable Preferred Units | Adjustment

49,946

Series B Redeemable Preferred Units | As Reported

(49,946)

Series B Redeemable Preferred Units | Adjustment

97,909

83,872

Series C Redeemable Preferred Units | As Reported

(97,909)

$ (97,909)

$ (83,872)

Series C Redeemable Preferred Units | Adjustment

124,841

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

$ (124,841)

[1]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of that date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	The consolidated balance sheet as of December 31, 2020 is derived from the audited consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[3]	The consolidated balance sheet as of December 31, 2019 is derived from the audited consolidated financial statements as of such date and was retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. Changes in stockholders’ equity for the three months ended March 31, 2020, June 30, 2020 and September 30, 2020 were also retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts Payable And Accrued Liabilities Current [Abstract]
Accrued bonus	$ 1,764	$ 1,763
Professional fees	755	1,018
Research and development costs	3,223	1,829
Other	97	31
Accrued expenses and other current liabilities	$ 5,839	$ 4,641

License and Collaboration Agreements - Summary of Research and Development Costs Related to Collaboration and License Agreements (Details) - USD ($)
$ in Thousands

1 Months Ended

3 Months Ended

9 Months Ended

Jan. 31, 2021

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2021

Sep. 30, 2020

Collaboration and License Agreements

$ 12,680

$ 9,913

$ 36,873

$ 26,582

^[1]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreements | Cullinan Oncology - Adimab

1,443

3,117

2,341

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreements | Amber - MIT

$ 46

318

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreements | Apollo - Wistar

276

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreements | Florentine - Tubingen

304

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreements | Pearl - Taiho

912

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License And Collaboration Agreements [Line Items]

$ 3,000

$ 531

$ 3,000

$ 531

[1]

License and Collaboration Agreements - Additional Information (Details) - USD ($)

1 Months Ended

3 Months Ended

9 Months Ended

Dec. 31, 2020

Jan. 31, 2021

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2021

Sep. 30, 2020

Net upfront revenue

$ 18,943,000

Collaboration and License Agreements

$ 12,680,000

$ 9,913,000

36,873,000

$ 26,582,000

^[1]

License And Collaboration Agreements [Line Items]

Pearl—Zai Lab License Agreement

$ 46,000

1,443,000

3,117,000

2,341,000

License And Collaboration Agreements [Line Items]

Nonrefundable license fee

$ 20,000,000.0

Net upfront revenue

18,900,000

Pearl—Zai Lab License Agreement | Maximum

License And Collaboration Agreements [Line Items]

Aggregate amount of milestone payment

$ 211,000,000.0

Pearl - Taiho | Collaboration and License Agreements

License And Collaboration Agreements [Line Items]

$ 3,000,000.0

$ 531,000

$ 3,000,000

$ 531,000

[1]

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
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-Paragraph 4
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (a)
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Cullinan-MICA Asset Acquisition - Additional Information (Details)		1 Months Ended		9 Months Ended
	May 28, 2020 USD ($) shares	Jun. 30, 2021 USD ($) shares	May 31, 2020 shares	Sep. 30, 2021 USD ($) Milestone shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 shares
Schedule Of Asset Acquisition [Line Items]
Common stock, shares authorized				150,000,000		34,900,878
Common stock, shares outstanding				43,660,909		29,831,125
Voting agreement description				Voting Agreement dated May 28, 2020, among the Company and other stockholders of MICA, MICA increased the size of its board of directors from four to five directors, of which three directors are designated by the Company.
Acquired in-process research and development assets \| $					$ 6,447,000
PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Number of share authorized for issuance	72,890,797
Common stock, shares authorized	39,000,000
Preferred stock shares authorized	33,890,797
MICA
Schedule Of Asset Acquisition [Line Items]
Number of shares outstanding			22,829,406
Common stock, shares outstanding			602,784
MICA Equity Plan
Schedule Of Asset Acquisition [Line Items]
Common stock, shares reserved			2,034,457
MICAs Directors and Officers, as well as Former Employees of PDI Therapeutics \| MICA Equity Plan
Schedule Of Asset Acquisition [Line Items]
Common stock, shares reserved			1,826,402
Series A Senior Preferred Stock
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition			5,385,787
Series A Senior Preferred Stock \| PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized	19,786,914
Series A Senior Preferred Stock \| MICA
Schedule Of Asset Acquisition [Line Items]
Ownership percentage in outstanding shares				88.50%
Series A Senior Preferred Stock \| MICA Board Authorized First Additional Closing
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition		5,385,787
Share purchased price as part of asset acquisition \| $		$ 7,100,000
Ownership percentage increased in outstanding shares		45.00%
Series A Senior Preferred Stock \| Certain Existing Shareholders \| MICA Board Authorized First Additional Closing
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition		702,495
Share purchased price as part of asset acquisition \| $		$ 900,000
Series A Junior Preferred Stock \| PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized	1,999,998
Series A Junior Preferred Stock \| MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares outstanding			6,088,282
Series A Junior Preferred Stock \| Cullinan Oncology, LLC
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares outstanding			5,385,787
Series A-1 Junior Preferred Stock \| PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized	652,371
Series A-2 Junior Preferred Stock \| PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares authorized	11,451,514
Series A, A-1 and A2 Junior Preferred Stock \| MICA
Schedule Of Asset Acquisition [Line Items]
Preferred stock shares outstanding			14,103,883
Fully Diluted Shares \| MICA
Schedule Of Asset Acquisition [Line Items]
Ownership percentage in outstanding shares				24.00%
Ownership percentage can increase with subsequent closings				54.00%
Research and Development Expense
Schedule Of Asset Acquisition [Line Items]
Acquired in-process research and development assets \| $					$ 6,400,000
Series A Senior Preferred Stock Purchase Agreement
Schedule Of Asset Acquisition [Line Items]
Number of additional closings \| Milestone				2
Series A Senior Preferred Stock Purchase Agreement \| Series A Senior Preferred Stock \| PDI Therapeutics, Inc.
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition	5,385,787
Share purchased price as part of asset acquisition \| $	$ 7,100,000
Series A Senior Preferred Stock Purchase Agreement \| Series A Senior Preferred Stock \| PDI Therapeutics, Inc. \| Certain Existing PDI Therapeutics Shareholders
Schedule Of Asset Acquisition [Line Items]
Number of share purchased as part of asset acquisition	702,495
Share purchased price as part of asset acquisition \| $	$ 900,000
Series A Senior Preferred Stock Purchase Agreement \| Maximum
Schedule Of Asset Acquisition [Line Items]
Proceeds from preferred stock \| $				$ 26,000,000.0

Common Stock and Noncontrolling Interest in Subsidiaries - Additional Information (Details) - USD ($)

1 Months Ended

3 Months Ended

9 Months Ended

May 28, 2020

Jul. 31, 2021

Jun. 30, 2021

Dec. 31, 2020

Nov. 30, 2020

Aug. 31, 2020

May 31, 2020

Apr. 30, 2020

Feb. 28, 2019

Dec. 31, 2018

Sep. 30, 2021

Mar. 31, 2021

Sep. 30, 2020

Sep. 30, 2021

Sep. 30, 2020

Common stock, shares authorized

34,900,878

150,000,000

Dividends declared

$ 0

Common stock, voting rights

Each share of common stock entitles the holder to one vote and to receive dividends when and if declared by the board of directors of the Company.

29,831,125

43,660,909

$ (909,000)

$ (1,456,000)

$ (223,000)

$ (6,899,000)

^[1]

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

^[2]

14,250,000

MICA

3,367,804

$ 0.23

Ownership interest percentage

$ 800,000

45.00%

35.00%

MICA

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Equity at acquisition

$ 12,800,000

DFKZ and UFE Anti-dilution Shares

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Common Stock

License Agreement between Amber and Massachusetts Institute of Technology

13,685,000

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

License Agreement between Amber and Massachusetts Institute of Technology | Common Stock

153,229

400,132

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Tubingen License Agreement | Common Stock

$ 0

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Tubingen License Agreement | Common Stock | DFKZ and UFE Anti-dilution Shares

381,810

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Subscription Agreement between Company and Pearl | Common Stock

$ 0

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

$ 0.44

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

$ 1,200,000

Purchase of shares

2,730,227

Series A Preferred Stock

Shares issued

3,000,000

$ 3,000,000.0

$ 6,000,000.0

$ 9,000,000.0

$ 7,000,000.0

9,000,000

7,000,000

$ 1.00

Series A Preferred Stock | Taiho Ventures, LLC

6,000,000

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

$ 14,000,000.0

14,000,000

Series A Preferred Stock | Taiho License Agreement

$ 1.00

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

1,206,000

1,860,000

$ 0

Series A Preferred Stock | Maximum

$ 0

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Series A Preferred Stock | Maximum | Taiho Ventures, LLC

11,000,000

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

23,000,000

Series B Preferred Units

$ 8,100,000

Series A Senior Preferred Stock

7,500,000

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares issued

6,088,282

Number of share purchased as part of asset acquisition

$ 1.31

5,385,787

Series A Senior Preferred Stock | MICA

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Equity at acquisition

7,100,000

Junior Preferred and Common Stockholders | Noncontrolling Interest in Subsidiaries | MICA

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Equity at acquisition

$ 5,700,000

Cullinan Amber Corp | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Amber Corp | Maximum | HLBV

(200,000)

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Amber Corp | Series A Preferred Stock

(100,000)

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Shares issued

3,000,000

Cullinan Amber Corp | Series A Preferred Stock | Maximum

$ 3,000,000.0

Closing price per share

$ 1.00

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Sale of stock

9,000,000

Cullinan Apollo Corp

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Florentine Corp | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Florentine Corp | Tubingen License Agreement

(300,000)

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Florentine Corp | Tubingen License Agreement | Common Stock

725,118

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Florentine Corp | Series A Preferred Stock

$ 0

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Cullinan Florentine Corp | Series A Preferred Stock | Maximum

$ 6,000,000.0

Sale of stock

6,000,000

Closing price per share

$ 1.00

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Sale of stock

6,000,000

MICA | HLBV

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

(300,000)

(800,000)

(5,100,000)

MICA | Maximum | HLBV

Cullinan Pearl Corp | HLBV

(100,000)

Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]

$ (600,000)

$ (900,000)

$ 700,000

$ (1,300,000)

[1]	The shares and per share amounts for the nine months ended September 30, 2020 were derived from the unaudited consolidated financial statements as of that date and were retroactively adjusted as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.
[2]	Changes in equity activities for the nine months ended September 30, 2020 were retroactively adjusted, including shares and per share amounts, as a result of the Reorganization and Reverse Stock Split. See Note 3 to the unaudited consolidated financial statements for additional details.

Equity-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense		$ 12,230
Common stock, shares issued	43,660,909	43,660,909		29,831,125
2021 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved	12,546,386	12,546,386
Split-adjusted restricted stock issued	320,228	320,228
Common stock issuable upon exercise of stock options	4,616,187	4,616,187
Common stock issuable upon exercise of stock options, weighted average exercise price		$ 4.30
Increase in number of shares reserved and available for issuance percentage	5.00%	5.00%
2021 Stock Plan \| Executive Officers, Employees and Affiliates
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock issuable upon exercise of stock options	1,753,316	1,753,316
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved	416,665	416,665
Increase in number of shares reserved and available for issuance percentage	1.00%	1.00%
Increase in number of shares reserved and available for issuance	833,330	833,330
Common stock, shares issued			10,099
ESPP \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity-based compensation expense	$ 100	$ 100

Equity-Based Compensation - Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 4,557	$ 12,230
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	2,458	6,320
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 2,099	$ 5,910

Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Royalty percentage				1.00%
Royalties under obligation				$ 0		$ 0
Globeways Holdings Limited \| 2020 Consulting Agreement
Related Party Transaction [Line Items]
Related party transaction, description of transaction				In April 2020, the Company entered into a consulting agreement (the 2020 Consulting Agreement) with Globeways Holdings Limited, or Globeways. Globeways and entities affiliated with F2 Ventures beneficially own in the aggregate greater than five percent of the Company’s outstanding units and Globeways is beneficially owned by a member of the Company’s board of directors.
Consulting fee per month	$ 25,000
MPM Oncology Charitable Foundation, Inc.
Related Party Transaction [Line Items]
Royalty percentage				0.50%
UBS Optimus Foundation
Related Party Transaction [Line Items]
Royalty percentage				0.50%
Maximum \| Globeways Holdings Limited \| 2020 Consulting Agreement
Related Party Transaction [Line Items]
Consulting fee		$ 0	$ 100,000	$ 100,000	$ 200,000

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0	$ 0	$ 0	$ 0
Benefits of federal and state deferred tax assets recognized	$ 0		$ 0

Net loss attributable to common stockholders of Cullinan

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Commitments and Contingencies - Additional Information (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2017 ft²	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Lessee Lease Description [Line Items]
Rent expense \| $		$ 0.2	$ 0.2	$ 0.5	$ 0.4
Operating lease commence date	Feb. 01, 2018
Operating lease expiration date				Jun. 30, 2024
Massachusetts
Lessee Lease Description [Line Items]
Operating lease rentable area \| ft²	7,531

Commitments and Contingencies - Summary of Future Minimum Payments Due Under Operating Lease (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Remainder of 2021	$ 150
2022	608
2023	618
2024	313
Future minimum payments due under operating lease	$ 1,689

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Maximum \| 401(K) Plan
Defined Benefit Plan Disclosure [Line Items]
Expense relating to matching contribution	$ 0.1	$ 0.1	$ 0.2	$ 0.1

Net Loss per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

9 Months Ended

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2021

Sep. 30, 2020

^[1]

Numerator:

$ (17,350)

$ (9,858)

$ (33,056)

$ (23,453)

Denominator

Total weighted-average shares used in computing net loss per share, basic and diluted

43,438,861

19,721,992

43,254,230

19,453,479

Net Loss per Share:

$ (0.40)

$ (0.50)

$ (0.76)

$ (1.21)

[1]