Cullinan Oncology (CGEM) 10-Q 7 Nov 24 2024 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Oct. 31, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Registrant Name	CULLINAN THERAPEUTICS, INC.
Current Fiscal Year End Date	--12-31
Document Quarterly Report	true
Document Transition Report	false
Entity Central Index Key	0001789972
Securities Act File Number	001-39856
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-3879991
Entity Address, Address Line One	One Main Street
Entity Address, Address Line Two	Suite 1350
Entity Address, City or Town	Cambridge
Entity Address, Country	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	410-4650
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	CGEM
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		58,227,593

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 102,085	$ 98,434
Short-term investments	475,993	368,633
Prepaid expenses and other current assets	13,961	13,124
Total current assets	592,039	480,191
Property and equipment, net	760	989
Operating lease right-of-use assets	2,019	2,543
Other assets	460	459
Long-term investments	57,976	0
Total assets	653,254	484,182
Current liabilities:
Accounts payable	2,115	2,493
Accrued expenses and other current liabilities	20,831	24,204
Operating lease liabilities, current	1,258	1,440
Total current liabilities	24,204	28,137
Long-term liabilities:
Operating lease liabilities, net of current portion	1,188	2,150
Total liabilities	25,392	30,287
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2024 and December 31, 2023; 647,500 shares issued and outstanding as of September 30, 2024 and December 31, 2023.	0	0
Common stock, $0.0001 par value, 150,000,000 shares authorized as of September 30, 2024 and December 31, 2023; 58,141,130 and 42,900,083 shares issued and outstanding as of September 30, 2024 and December 31, 2023, respectively	6	4
Additional paid-in capital	947,479	654,685
Accumulated other comprehensive income (loss)	970	(129)
Accumulated deficit	(320,593)	(200,857)
Total Cullinan stockholders' equity	627,862	453,703
Noncontrolling interests	0	192
Total stockholders' equity	627,862	453,895
Total liabilities and stockholders' equity	$ 653,254	$ 484,182

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred Stock par value	$ 0.0001	$ 0.0001
Preferred Stock, shares authorized	10,000,000	10,000,000
Preferred Stock, Share issued	647,500	647,500
Preferred stock, Share Outstanding	647,500	647,500
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common Stock, Shares Issued	58,141,130	42,900,083
Common stock, shares outstanding	58,141,130	42,900,083

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Operating expenses:
Research and development	$ 35,506	$ 33,821	$ 102,411	$ 113,308
General and administrative	13,349	10,982	39,460	31,856
Total operating expenses	48,855	44,803	141,871	145,164
Impairment of long-lived assets	0	(440)	0	(440)
Loss from operations	(48,855)	(45,243)	(141,871)	(145,604)
Other income (expense):
Interest income	8,384	5,880	22,148	15,710
Other income (expense), net	(89)	180	(205)	356
Net Loss	(40,560)	(39,183)	(119,928)	(129,538)
Net loss attributable to noncontrolling interests	0	0	(192)	(179)
Net loss attributable to common stockholders of Cullinan	(40,560)	(39,183)	(119,736)	(129,359)
Comprehensive income (loss):
Net loss	(40,560)	(39,183)	(119,928)	(129,538)
Unrealized gain on investments	1,446	574	1,099	1,550
Comprehensive loss	(39,114)	(38,609)	(118,829)	(127,988)
Comprehensive loss attributable to noncontrolling interests	0	0	(192)	(179)
Comprehensive loss attributable to Cullinan	$ (39,114)	$ (38,609)	$ (118,637)	$ (127,809)
Net loss per share attributable to common stockholders of Cullinan:
Net loss per share, basic	$ (0.69)	$ (0.91)	$ (2.3)	$ (3.15)
Net loss per share, diluted	$ (0.69)	$ (0.91)	$ (2.3)	$ (3.15)
Weighted-average shares used in computing net loss per share attributable to common stockholders of Cullinan
Weighted-average common stock outstanding - basic	58,337	42,734	52,157	41,130
Weighted-average common stock outstanding - diluted	58,337	42,734	52,157	41,130

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Noncontrolling Interest
Balances at Dec. 31, 2022	$ 535,029		$ 5	$ 585,320	$ (2,601)	$ (47,695)
Balances, shares at Dec. 31, 2022			45,796,449
Contributions from noncontrolling interests	179						$ 179
Issuance of preferred stock in exchange for common stock, Share		647,500	(6,475,000)
Issuance of preferred stock in exchange for common stock			$ (1)	1
Net issuance of common stock under equity-based compensation plans	(36)			(36)
Net issuance of common stock under equity-based compensation plans, shares			22,152
Equity-based compensation	7,259			7,259
Unrealized gain (loss) on investments	1,359				1,359
Net Loss	(58,141)					(57,962)	(179)
Balances at Mar. 31, 2023	485,649		$ 4	592,544	(1,242)	(105,657)
Balances, shares at Mar. 31, 2023		647,500	39,343,601
Balances at Dec. 31, 2022	535,029		$ 5	585,320	(2,601)	(47,695)
Balances, shares at Dec. 31, 2022			45,796,449
Issuance of common stock and pre-funded warrants, net of issuance costs	(38,388)
Acquisition of noncontrolling interests	0
Unrealized gain (loss) on investments	1,550
Net Loss	(129,538)
Balances at Sep. 30, 2023	468,817		$ 4	646,918	(1,051)	(177,054)
Balances, shares at Sep. 30, 2023		647,500	42,760,644
Balances at Mar. 31, 2023	485,649		$ 4	592,544	(1,242)	(105,657)
Balances, shares at Mar. 31, 2023		647,500	39,343,601
Net issuance of common stock under equity-based compensation plans	214			214
Net issuance of common stock under equity-based compensation plans, shares			81,703
Equity-based compensation	7,920			7,920
Unrealized gain (loss) on investments	(383)				(383)
Issuance of common stock	38,388			38,388
Issuance of common stock, shares			3,310,000
Net Loss	(32,214)					(32,214)
Balances at Jun. 30, 2023	499,574		$ 4	639,066	(1,625)	(137,871)
Balances, shares at Jun. 30, 2023		647,500	42,735,304
Net issuance of common stock under equity-based compensation plans	112			112
Net issuance of common stock under equity-based compensation plans, shares			25,340
Equity-based compensation	7,740			7,740
Unrealized gain (loss) on investments	574				574
Net Loss	(39,183)					(39,183)
Balances at Sep. 30, 2023	468,817		$ 4	646,918	(1,051)	(177,054)
Balances, shares at Sep. 30, 2023		647,500	42,760,644
Balances at Dec. 31, 2023	453,895		$ 4	654,685	(129)	(200,857)	192
Balances, shares at Dec. 31, 2023		647,500	42,900,083
Net issuance of common stock under equity-based compensation plans	1,085			1,085
Net issuance of common stock under equity-based compensation plans, shares			165,562
Equity-based compensation	8,227			8,227
Unrealized gain (loss) on investments	(202)				(202)
Net Loss	(37,340)					(37,148)	(192)
Balances at Mar. 31, 2024	425,665		$ 4	663,997	(331)	(238,005)
Balances, shares at Mar. 31, 2024		647,500	43,065,645
Balances at Dec. 31, 2023	453,895		$ 4	654,685	(129)	(200,857)	$ 192
Balances, shares at Dec. 31, 2023		647,500	42,900,083
Issuance of common stock and pre-funded warrants, net of issuance costs	(262,652)
Acquisition of noncontrolling interests	(4,448)
Unrealized gain (loss) on investments	1,099
Net Loss	(119,928)
Balances at Sep. 30, 2024	627,862		$ 6	947,479	970	(320,593)
Balances, shares at Sep. 30, 2024		647,500	58,141,130
Balances at Mar. 31, 2024	425,665		$ 4	663,997	(331)	(238,005)
Balances, shares at Mar. 31, 2024		647,500	43,065,645
Net issuance of common stock under equity-based compensation plans	3,336		$ 1	3,335
Issuance of common stock and pre-funded warrants net of issuance costs, Shares			14,421,070
Issuance of common stock and pre-funded warrants, net of issuance costs	262,652		$ 1	262,651
Net issuance of common stock under equity-based compensation plans, shares			384,923
Equity-based compensation	10,533			10,533
Acquisition of noncontrolling interests	(3,792)			(3,792)
Unrealized gain (loss) on investments	(145)				(145)
Net Loss	(42,028)					(42,028)
Balances at Jun. 30, 2024	656,221		$ 6	936,724	(476)	(280,033)
Balances, shares at Jun. 30, 2024		647,500	57,871,638
Net issuance of common stock under equity-based compensation plans	1,981			1,981
Net issuance of common stock under equity-based compensation plans, shares			269,492
Equity-based compensation	9,430			9,430
Acquisition of noncontrolling interests	(656)			(656)
Unrealized gain (loss) on investments	1,446				1,446
Net Loss	(40,560)					(40,560)
Balances at Sep. 30, 2024	$ 627,862		$ 6	$ 947,479	$ 970	$ (320,593)
Balances, shares at Sep. 30, 2024		647,500	58,141,130

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating activities:
Net loss	$ (119,928)	$ (129,538)
Adjustments to reconcile net loss to net cash used in operating activities:
Equity-based compensation expense	28,190	22,919
Accretion on marketable securities	(11,958)	(6,533)
Depreciation and amortization	229	233
Impairment of long-lived assets	0	440
Realized gain on marketable securities	0	(20)
Non-cash contributions from noncontrolling interests	0	4
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(837)	(2,650)
Accounts payable	(378)	(1,709)
Accrued expenses and other current liabilities	(3,995)	4,992
Income tax payable	0	(4,282)
Net cash used in operating activities	(108,677)	(116,144)
Investing activities:
Purchase of marketable securities	(553,095)	(307,371)
Maturities of marketable securities	400,817	291,915
Purchase of property and equipment	0	(208)
Net cash used in investing activities	(152,278)	(15,664)
Financing activities:
Issuance of common stock and pre-funded warrants, net of issuance costs	262,652	38,388
Net issuance of common stock under equity-based compensation plans	6,402	290
Acquisition of noncontrolling interests	(4,448)	0
Issuance of convertible notes	0	1,825
Net cash provided by financing activities	264,606	40,503
Net increase (decrease) in cash and cash equivalents	3,651	(91,305)
Cash and cash equivalents at beginning of period	98,434	156,152
Cash and cash equivalents at end of period	102,085	64,847
Non-cash financing activities and supplemental cash flow information
Cash paid (refunded) for income taxes	(2,274)	4,708
Conversion of convertible note into noncontrolling interest	$ 0	$ 175

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (40,560)	$ (39,183)	$ (119,736)	$ (129,359)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2024
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 Therapeutics, Inc., together with its consolidated subsidiaries ("Cullinan" or the "Company"), is a clinical-stage biopharmaceutical company dedicated to creating new standards of care for patients that was incorporated in September 2016 and has a principal place of business in Cambridge, Massachusetts. In April 2024, the Company changed its name from Cullinan Oncology, Inc. to Cullinan Therapeutics, Inc. Liquidity The Company has a history of significant operating losses and has had negative cash flows from operations since its inception and expects to continue to generate operating losses for the foreseeable future. Cullinan’s ultimate success depends on the outcome of its research and development activities as well as its ability to commercialize the Company’s product candidates. Cullinan 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 Cullinan’s expectations for a number of reasons, including reasons beyond the Company’s control. Since inception, Cullinan has funded its operations primarily through the sale of equity securities and from licensing or selling the rights to its product candidates. The Company expects that its cash, cash equivalents, and short-term investments of $ 578.1 million , and long-term investments and interest receivable of $ 60.9 million as of September 30, 2024, will be sufficient to fund its operating expenses and capital expenditure requirements through the next twelve months from the date of issuance of these consolidated financial statements. In April 2024, Cullinan sold shares of its common stock and pre-funded warrants for shares of its common stock in a private placement (the “2024 Private Placement”) for net proceeds of $ 262.7 million , after deducting offering costs of $ 17.3 million . Refer to Note 6 for additional detail regarding the 2024 Private Placement.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	(2) Summary of Significant Accounting Policies Cullinan’s significant accounting policies have not changed materially from those disclosed in its annual audited consolidated financial statements and accompanying notes in its Annual Report on Form 10-K for the fiscal year ended December 31, 2023 (the “2023 10-K”). 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 ("U.S. GAAP") and in accordance with applicable rules and regulations of the Securities and Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage therapeutics. In the opinion of Cullinan’s management, the unaudited consolidated financial statements reflect all adjustments, which are normal and recurring in nature, and necessary for fair financial statement presentation. The preparation of these unaudited consolidated financial statements and accompanying notes in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported. Actual results could differ materially from those estimates. These unaudited consolidated financial statements and accompanying notes should be read in conjunction with the Company’s annual audited consolidated financial statements and accompanying notes included in the 2023 10-K. Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (the “FASB”) issued an accounting standards update to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The main provisions of this update require companies to disclose, on an annual and interim basis, significant segment expenses, segment profit and loss, and other segments items that are regularly provided to the Company's Chief Operating Decision Maker (the "CODM"). This update also requires companies to disclose the title and position of the CODM and to explain how the CODM uses the reported segment measures in assessing segment performance and deciding how to allocate resources. The update also requires companies with a single reportable segment to provide all required segment reporting disclosures. This new standard will be effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. Cullinan adopted this standard on January 1, 2024 for 2024 annual reporting and interim periods beginning in 2025. Recently Issued Accounting Pronouncements Cullinan currently qualifies as an emerging growth company (“EGC”) under the Jumpstart Our Business Startups Act, which allows the Company to delay adoption of certain accounting standards until those standards would otherwise apply to private companies. The Company has elected to use the extended transition period for new or revised accounting standards during the period in which it remains an EGC; however, Cullinan may adopt certain new or revised accounting standards early. Based on the market value of the Company's common stock held by non-affiliates as of June 30, 2024, the Company will cease to be an EGC as of December 31, 2024. As a result, beginning with the Company’s Annual Report on Form 10-K for the year ending December 31, 2024, the Company will not be able to rely on the extended transition period noted above and will be required to adopt all new accounting pronouncements within the same time periods as other public companies that are not EGCs. In December 2023, the FASB issued an accounting standards update to enhance transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The main provisions in this update will require companies to disclose, on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update will also require companies to disclose, on an annual basis, the amount of income taxes paid, income (or loss) from continuing operations before income tax expense (or benefit), and income tax expense (or benefit) from continuing operations, disaggregated by federal, state, and foreign jurisdictions. This new standard will be effective for fiscal years beginning after December 15, 2024, and early adoption is permitted. The Company expects that it will adopt this new standard on January 1, 2025. The Company is evaluating the impact this new standard will have on its consolidated financial statements and associated disclosures.

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2024
Financial Instruments Pledged as Collateral [Abstract]
Financial Instruments	(3) Financial Instruments Investments Cullinan recognized its investments by security type at September 30, 2024 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 227,900 $ 244 $ ( 1 ) $ 228,143 Corporate notes 222,233 640 ( 10 ) 222,863 Asset-backed securities 24,932 55 — 24,987 Total short-term investments 475,065 939 ( 11 ) 475,993 Long-term investments Corporate notes 57,934 98 ( 56 ) 57,976 Total long-term investments 57,934 98 ( 56 ) 57,976 Total investments $ 532,999 $ 1,037 $ ( 67 ) $ 533,969 Cullinan recognized its investments by security type at December 31, 2023 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 208,289 $ 221 $ ( 16 ) $ 208,494 Corporate notes 99,359 27 ( 275 ) 99,111 Asset-backed securities 61,114 3 ( 89 ) 61,028 Total short-term investments 368,762 251 ( 380 ) 368,633 Total investments $ 368,762 $ 251 $ ( 380 ) $ 368,633 Fair Value of Financial Instruments The following table sets forth the fair value of Cullinan’s financial assets that were measured at fair value on a recurring basis as of September 30, 2024 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 228,143 $ — $ 228,143 Corporate notes — 222,863 — 222,863 Asset-backed securities — 24,987 — 24,987 Total short-term investments — 475,993 — 475,993 Long-term investments Corporate notes — 57,976 — 57,976 Total long-term investments — 57,976 — 57,976 Total investments $ — $ 533,969 $ — $ 533,969 The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of December 31, 2023 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 208,494 $ — $ 208,494 Corporate notes — 99,111 — 99,111 Asset-backed securities — 61,028 — 61,028 Total short-term investments — 368,633 — 368,633 Total investments $ — $ 368,633 $ — $ 368,633 As of September 30, 2024 and December 31, 2023 , the fair values of Cullinan's cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities approximated their carrying values due to the short-term nature of these instruments.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2024
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 consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, 2024 December 31, 2023 Contracted research and development expenses $ 8,226 $ 8,434 Due to Taiho under collaboration agreement, net 5,026 7,869 Employee compensation 5,870 6,987 Other current liabilities 1,709 914 Total accrued expenses and other current liabilities $ 20,831 $ 24,204

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2024
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	(5) License and Collaboration Agreements Harbour License Agreement In February 2023, the Company and Harbour BioMed US Inc. (“Harbour”) entered into a license and collaboration agreement (the “Harbour License Agreement”), pursuant to which Harbour granted to Cullinan an exclusive license for the development, manufacturing and commercialization of HBM7008 (CLN-418) in the U.S. Under the terms of the Harbour License Agreement, Cullinan paid Harbour an upfront license fee of $ 25.0 million at signing. In addition, under the Harbour License Agreement, Harbour granted Cullinan certain intellectual property rights to enable the Company to perform its obligations and exercise its rights under the Harbour License Agreement. Cullinan evaluated the Harbour License Agreement and determined that the exclusive license for the development, manufacturing and commercialization of HBM7008 (CLN-418) in the U.S. represented an asset acquisition of in-process research and development. The Company also determined that the asset had no alternative future use at the time of acquisition, and therefore, the upfront license fee of $ 25.0 million was recorded within research and development expenses for the nine months ended September 30, 2023. In August 2024, following a review of the data from the Phase 1 clinical trial of CLN-418, the Company notified Harbour of its decision to terminate the Harbour License Agreement, effective November 2024. In connection with the termination, the Company discontinued development of CLN-418 and returned development and commercial rights for CLN-418 to Harbour. Taiho Agreements Cullinan has a co-development agreement with an affiliate of Taiho Pharmaceutical Co., Ltd ("Taiho"), pursuant to which the Company is collaborating to develop zipalertinib and has the option to co-commercialize zipalertinib in the U.S. Development costs for zipalertinib are shared equally between Taiho and the Company with each party receiving 50 % of any future pre-tax profits from potential U.S. sales of zipalertinib. The Company concluded that the co-development agreement with Taiho is a collaborative arrangement because Cullinan is an active participant in the development of zipalertinib. Payments made to or received from Taiho for zipalertinib development activities after the execution of the co-development agreement are recorded within research and development expenses and general and administrative expenses. For the three and nine months ended September 30, 2024 , the Company recorded $ 6.5 million and $ 17.6 million, respectively, related to its share of research and development costs incurred by Taiho. For the three and nine months ended September 30, 2024 , the Company recorded $ 0.7 million related to its share of general and administrative costs incurred by Taiho. Cullinan incurred $ 2.2 million and $ 6.9 million of costs that were reimbursable by Taiho during the three and nine months ended September 30, 2024, respectively, which were recorded as a reduction to research and development expenses. For the three and nine months ended September 30, 2023 , the Company recorded $ 5.4 million and $ 15.6 million, respectively, related to its share of research and development costs incurred by Taiho. Cullinan incurred $ 2.0 million and $ 5.1 million of research and development costs that were reimbursable by Taiho during the three and nine months ended September 30, 2023 , respectively, which were recorded as a reduction to research and development expenses. The net amounts of $ 5.0 million and $ 7.9 million due to Taiho as of September 30, 2024 and December 31, 2023, respectively, were recorded within accrued expenses and other current liabilities. Cullinan is also eligible to receive up to $130.0 million from Taiho tied to epidermal growth factor receptor exon 20 non-small-cell lung cancer regulatory milestones. Other License and Collaboration Agreements During the three and nine months ended September 30, 2024, no milestones were achieved under the Company’s other license and collaboration agreements. During each of the three and nine months ended September 30, 2023 , Cullinan recorded $ 0.5 million in research and development expenses for milestones achieved under its collaboration agreement with Adimab, LLC for CLN-978. During the nine months ended September 30, 2023 , Cullinan recorded $ 0.2 million in research and development expenses for milestones achieved under its license agreement with the Massachusetts Institute of Technology for CLN-617.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2024
Stockholders' Equity Note [Abstract]
Stockholders' Equity	(6) Stockholders' Equity Common Stock 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, 2024. 2024 Private Placement In April 2024, Cullinan completed the 2024 Private Placement in which Cullinan issued approximately 14.4 million shares of its common stock and pre-funded warrants to purchase approximately 0.3 million additional shares of its common stock. Cullinan received net proceeds of $ 262.7 million from the 2024 Private Placement, after deducting offering costs of $ 17.3 million . Refer to the discussion under the heading “Warrants” below for further detail regarding the pre-funded warrants. At-the-Market Equity Offering Program In May 2023, Cullinan entered into an agreement with Cowen and Company, LLC (“Cowen”) to establish an at-the-market equity offering program (the “ATM") pursuant to which the Company may offer and sell up to $ 125.0 million of its common stock from time to time through Cowen, acting as its sales agent. The Company made no sales under the ATM in the nine months ended September 30, 2024. Through September 30, 2024 , the Company has sold approximately 3.3 million shares under the ATM and received net proceeds of $ 38.4 million after deducting commissions. As of September 30, 2024 , Cullinan had $ 85.6 million in shares of its common stock remaining under the ATM. Preferred Stock In January 2023, the Company entered into an exchange agreement with Biotechnology Value Fund, L.P., Biotechnology Value Fund II, L.P., Biotechnology Value Trading Fund OS LP, and MSI BVF SPV, LLC (the “Stockholders”), pursuant to which the Stockholders exchanged 6.5 million shares of Cullinan’s common stock for 0.6 million shares of newly designated Series A convertible preferred stock, a “toothless” preferred stock, par value $ 0.0001 per share. Each share of the preferred stock will be convertible into ten shares of common stock at the option of the holder at any time, subject to certain limitations, including that the holder will be prohibited from converting preferred stock into common stock if, as a result of such conversion, the holder, together with its affiliates, would beneficially own a number of shares of common stock more than 9.99 % of the total common stock then issued and outstanding immediately following the conversion of such shares of preferred stock. Holders of the preferred stock are permitted to increase this percentage to an amount not to exceed 19.99 % upon 60 days notice. Shares of preferred stock will generally have no voting rights, except as required by law and except that the consent of a majority of the holders of the outstanding preferred stock will be required to amend the terms of the preferred stock. In the event of the Company’s liquidation, dissolution or winding up, holders of preferred stock will participate pari passu with any distribution of proceeds to holders of common stock. Holders of preferred stock are entitled to receive when, as, and if dividends are declared and paid on the common stock, an equivalent dividend, calculated on an as-converted basis. Shares of preferred stock are otherwise not entitled to dividends. The preferred stock ranks (i) senior to any class or series of capital stock of Cullinan hereafter created specifically ranking by its terms junior to the preferred stock; (ii) on parity with the common stock and any class or series of capital stock of the Company created specifically ranking by its terms on parity with the preferred stock; and (iii) junior to any class or series of capital stock of Cullinan created specifically ranking by its terms senior to any preferred stock, in each case, as to distributions of assets upon liquidation, dissolution or winding up of the Company, whether voluntarily or involuntarily. The Company determined that the preferred stock should be classified as permanent equity. Noncontrolling Interests Certain of the Company's clinical-stage product candidates are held through development subsidiaries in which the Company has controlling interests. These development subsidiaries have issued common stock and preferred stock to the Company and to third parties. The holders of subsidiary common stock and preferred stock are generally 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 preferred stock of the respective subsidiary. The following table shows the Company’s ownership interest as of September 30, 2024 and December 31, 2023, respectively, in product candidates in which the Company has a controlling interest: Ownership Interest as of Product Candidate September 30, 2024 December 31, 2023 CLN-619 99 % 95 % CLN-049 97 % 96 % CLN-617 94 % 94 % During the nine months ended September 30, 2024 , Cullinan paid $ 4.4 million to acquire shares and options to purchase shares of its CLN-619 development subsidiary that were held by noncontrolling interests. Warrants As of September 30, 2024 , the Company had potentially issuable shares of common stock related to unexercised pre-funded warrants to purchase 0.3 million shares of the Company’s common stock at an exercise price of $ 0.001 per share. The pre-funded warrants may be exercised at the option of the holder at any time, subject to certain limitations. The exercise price and the number of shares are subject to adjustment for certain dividend payments and upon reclassification, exchange, combination or substitution of the shares of common stock. The pre-funded warrants expire in April 2054 if they have not been exercised by that time. Cullinan determined that the pre-funded warrants should be equity-classified. The Company also determined that the pre-funded warrants should be included in the weighted-average shares used in computing basic net loss per share attributable to common stockholders of Cullinan.

Equity-Based Compensation

Equity-Based Compensation	9 Months Ended
	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Equity-Based Compensation	(7) Equity-Based Compensation Cullinan recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive income (loss) for the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 General and administrative $ 5,503 $ 4,536 $ 17,274 $ 13,412 Research and development 3,927 3,204 10,916 9,507 Total equity-based compensation $ 9,430 $ 7,740 $ 28,190 $ 22,919

Royalty Transfer Agreements

Royalty Transfer Agreements	9 Months Ended
	Sep. 30, 2024
Royalty Transfer Agreements [Abstract]
Royalty Transfer Agreements	(8) Royalty Transfer Agreements The Company's CLN-619, CLN-049, and CLN-617 development subsidiaries are each party to royalty transfer agreements with two charitable foundations. Under these royalty transfer agreements, the charitable foundations are collectively entitled to receive a low single digit royalty percentage 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. Cullinan has deemed these royalty transfer agreements to be freestanding financial instruments that should be accounted for at fair value. The Company concluded that these instruments had no value at the inception of the agreements. Cullinan has not had any applicable net sales from its products and as a result, has no t paid or incurred any royalties under these agreements as of September 30, 2024. 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 September 30, 2024 and December 31, 2023 .

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	(9) Commitments and Contingencies The Company enters into contracts in the normal course of business with contract research organizations, contract manufacturing organizations, and other third parties for preclinical research studies, clinical trials and testing and manufacturing services. These agreements generally include cancellation clauses. Indemnification Agreements In the ordinary course of business, Cullinan may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and executive officers that will require Cullinan, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in certain cases, unlimited. To date, Cullinan has not incurred any material costs as a result of such indemnifications. The Company is not aware of any indemnification arrangements that could have a material effect on its financial position, results of operations or cash flows, and it has no t accrued any liabilities related to such obligations in its consolidated financial statements as of September 30, 2024 and December 31, 2023. Legal Proceedings Cullinan is not currently party to or aware of any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. Cullinan expenses as incurred the costs related to such legal proceedings.

Leases

Leases	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Leases	(10) Leases Cullinan has an operating lease for approximately 14,000 square feet of office space in a multi-tenant building in Cambridge, Massachusetts, which commenced in August 2022 and goes through July 2026. The Company also had an operating lease for approximately 8,000 square feet of office space in a multi-tenant building in Cambridge, Massachusetts, which commenced in February 2018 and expired in June 2024 (the "Suite 520 Lease"). Lease expense consisted of operating lease costs of $ 0.3 million and $ 0.9 million for the three and nine months ended September 30, 2024 , respectively. Lease expense consisted of operating lease costs of $ 0.4 million and $ 1.3 million for the three and nine months ended September 30, 2023, respectively. The following table summarizes supplemental cash flow information for the nine months ended September 30, 2024 and 2023 (in thousands): Nine Months Ended September 30, 2024 2023 Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 1,381 $ 1,378 The following table summarizes the Company’s future minimum lease payments as of September 30, 2024 (in thousands): September 30, 2024 Remainder of 2024 $ 357 2025 1,461 2026 871 Total future minimum lease payments 2,689 Less: imputed interest ( 243 ) Total lease liabilities at present value $ 2,446 The following table summarizes the weighted-average remaining lease term and discount rate as of September 30, 2024 and December 31, 2023: September 30, 2024 December 31, 2023 Weighted-average remaining lease term (in years) 1.8 2.4 Weighted-average discount rate 11.0 % 10.9 % Sublease Agreement Cullinan had a sublease agreement, which commenced in September 2022 and was scheduled to continue through May 2024 for the office space that the Company leased under the Suite 520 Lease. In September 2023, Cullinan and its subtenant cancelled the sublease agreement for the office space that the Company leased under the Suite 520 Lease, and Cullinan determined that the remaining right-of-use asset for the Suite 520 Lease and the related leasehold improvements (“Suite 520 Asset Group”) was not recoverable. Upon determining that the remaining Suite 520 Asset Group was not recoverable, the Company recorded an impairment of long-lived assets of $ 0.4 million for the carrying value in excess of the fair value of the Suite 520 Asset Group within income from operations in its consolidated statements of operations and other comprehensive income (loss) for the three and nine months ended September 30, 2023.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders of Cullinan	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders of Cullinan	(11) Net Loss per Share Attributable to Common Stockholders of Cullinan The following table sets forth the calculation of basic and diluted net loss per share attributable to common stockholders of Cullinan for the three and nine months ended September 30, 2024 and 2023 (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders of Cullinan $ ( 40,560 ) $ ( 39,183 ) $ ( 119,736 ) $ ( 129,359 ) Denominator: Weighted-average common stock outstanding — basic and diluted 58,337 42,734 52,157 41,130 Net loss per share attributable to common stockholders of Cullinan: Basic and diluted $ ( 0.69 ) $ ( 0.91 ) $ ( 2.30 ) $ ( 3.15 ) Cullinan used the treasury stock method for equity awards and the if-converted method for preferred stock to determine the number of dilutive shares. The following table sets forth potential common shares that were excluded from the computation of diluted net loss per share attributable to common stockholders of Cullinan for the nine months ended September 30, 2024 and 2023 because their effect would have been anti-dilutive (in thousands): Nine Months Ended September 30, 2024 2023 Stock options 8,411 9,355 Preferred stock 6,475 6,024 Restricted stock awards and units 328 158 Employee stock purchase plan 9 1 Total 15,223 15,538

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	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 ("U.S. GAAP") and in accordance with applicable rules and regulations of the Securities and Exchange Commission (the "SEC") for interim financial reporting and include the accounts of the Company and its consolidated subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The Company operates as one segment, which is developing early-stage therapeutics. In the opinion of Cullinan’s management, the unaudited consolidated financial statements reflect all adjustments, which are normal and recurring in nature, and necessary for fair financial statement presentation. The preparation of these unaudited consolidated financial statements and accompanying notes in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported. Actual results could differ materially from those estimates. These unaudited consolidated financial statements and accompanying notes should be read in conjunction with the Company’s annual audited consolidated financial statements and accompanying notes included in the 2023 10-K.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (the “FASB”) issued an accounting standards update to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The main provisions of this update require companies to disclose, on an annual and interim basis, significant segment expenses, segment profit and loss, and other segments items that are regularly provided to the Company's Chief Operating Decision Maker (the "CODM"). This update also requires companies to disclose the title and position of the CODM and to explain how the CODM uses the reported segment measures in assessing segment performance and deciding how to allocate resources. The update also requires companies with a single reportable segment to provide all required segment reporting disclosures. This new standard will be effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. Cullinan adopted this standard on January 1, 2024 for 2024 annual reporting and interim periods beginning in 2025.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements Cullinan currently qualifies as an emerging growth company (“EGC”) under the Jumpstart Our Business Startups Act, which allows the Company to delay adoption of certain accounting standards until those standards would otherwise apply to private companies. The Company has elected to use the extended transition period for new or revised accounting standards during the period in which it remains an EGC; however, Cullinan may adopt certain new or revised accounting standards early. Based on the market value of the Company's common stock held by non-affiliates as of June 30, 2024, the Company will cease to be an EGC as of December 31, 2024. As a result, beginning with the Company’s Annual Report on Form 10-K for the year ending December 31, 2024, the Company will not be able to rely on the extended transition period noted above and will be required to adopt all new accounting pronouncements within the same time periods as other public companies that are not EGCs. In December 2023, the FASB issued an accounting standards update to enhance transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The main provisions in this update will require companies to disclose, on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This update will also require companies to disclose, on an annual basis, the amount of income taxes paid, income (or loss) from continuing operations before income tax expense (or benefit), and income tax expense (or benefit) from continuing operations, disaggregated by federal, state, and foreign jurisdictions. This new standard will be effective for fiscal years beginning after December 15, 2024, and early adoption is permitted. The Company expects that it will adopt this new standard on January 1, 2025. The Company is evaluating the impact this new standard will have on its consolidated financial statements and associated disclosures.

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2024
Financial Instruments Pledged as Collateral [Abstract]
Schedule of Short-term and Long-term Investment Marketable Securities by Security Type	Investments Cullinan recognized its investments by security type at September 30, 2024 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 227,900 $ 244 $ ( 1 ) $ 228,143 Corporate notes 222,233 640 ( 10 ) 222,863 Asset-backed securities 24,932 55 — 24,987 Total short-term investments 475,065 939 ( 11 ) 475,993 Long-term investments Corporate notes 57,934 98 ( 56 ) 57,976 Total long-term investments 57,934 98 ( 56 ) 57,976 Total investments $ 532,999 $ 1,037 $ ( 67 ) $ 533,969 Cullinan recognized its investments by security type at December 31, 2023 as follows (in thousands): Amortized Gross Gross Estimated Short-term investments U.S. government notes $ 208,289 $ 221 $ ( 16 ) $ 208,494 Corporate notes 99,359 27 ( 275 ) 99,111 Asset-backed securities 61,114 3 ( 89 ) 61,028 Total short-term investments 368,762 251 ( 380 ) 368,633 Total investments $ 368,762 $ 251 $ ( 380 ) $ 368,633
Summary of Fair Value of Financial Assets Measured on Recurring Basis	The following table sets forth the fair value of Cullinan’s financial assets that were measured at fair value on a recurring basis as of September 30, 2024 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 228,143 $ — $ 228,143 Corporate notes — 222,863 — 222,863 Asset-backed securities — 24,987 — 24,987 Total short-term investments — 475,993 — 475,993 Long-term investments Corporate notes — 57,976 — 57,976 Total long-term investments — 57,976 — 57,976 Total investments $ — $ 533,969 $ — $ 533,969 The following table sets forth the fair value of the Company’s financial assets that were measured at fair value on a recurring basis as of December 31, 2023 (in thousands): Level 1 Level 2 Level 3 Total Short-term investments U.S. government notes $ — $ 208,494 $ — $ 208,494 Corporate notes — 99,111 — 99,111 Asset-backed securities — 61,028 — 61,028 Total short-term investments — 368,633 — 368,633 Total investments $ — $ 368,633 $ — $ 368,633

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2024
Accrued Expenses And Other Current Liabilities [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, 2024 December 31, 2023 Contracted research and development expenses $ 8,226 $ 8,434 Due to Taiho under collaboration agreement, net 5,026 7,869 Employee compensation 5,870 6,987 Other current liabilities 1,709 914 Total accrued expenses and other current liabilities $ 20,831 $ 24,204

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2024
Common Stock And Noncontrolling Interest In Subsidiaries [Abstract]
Schedule of Development Subsidiaries and Their Product Candidates	Ownership Interest as of Product Candidate September 30, 2024 December 31, 2023 CLN-619 99 % 95 % CLN-049 97 % 96 % CLN-617 94 % 94 % During the nine months ended September 30, 2024 , Cullinan paid $ 4.4 million to acquire shares and options to purchase shares of its CLN-619 development subsidiary that were held by noncontrolling interests. Warrants As of September 30, 2024 , the Company had potentially issuable shares of common stock related to unexercised pre-funded warrants to purchase 0.3 million shares of the Company’s common stock at an exercise price of $ 0.001 per share. The pre-funded warrants may be exercised at the option of the holder at any time, subject to certain limitations. The exercise price and the number of shares are subject to adjustment for certain dividend payments and upon reclassification, exchange, combination or substitution of the shares of common stock. The pre-funded warrants expire in April 2054 if they have not been exercised by that time. Cullinan determined that the pre-funded warrants should be equity-classified. The Company also determined that the pre-funded warrants should be included in the weighted-average shares used in computing basic net loss per share attributable to common stockholders of Cullinan.

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Equity-based Compensation Expense Categories In Consolidated Statements of Operations and Comprehensive Income (Loss)	Cullinan recorded equity-based compensation in the following expense categories in the consolidated statements of operations and comprehensive income (loss) for the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 General and administrative $ 5,503 $ 4,536 $ 17,274 $ 13,412 Research and development 3,927 3,204 10,916 9,507 Total equity-based compensation $ 9,430 $ 7,740 $ 28,190 $ 22,919

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Supplemental Cash Flow Information Relating to Leases	The following table summarizes supplemental cash flow information for the nine months ended September 30, 2024 and 2023 (in thousands): Nine Months Ended September 30, 2024 2023 Cash paid for amounts included in measurement of lease liabilities: Operating cash flows from operating leases $ 1,381 $ 1,378
Summarizes of Future Minimum Lease Payments	The following table summarizes the Company’s future minimum lease payments as of September 30, 2024 (in thousands): September 30, 2024 Remainder of 2024 $ 357 2025 1,461 2026 871 Total future minimum lease payments 2,689 Less: imputed interest ( 243 ) Total lease liabilities at present value $ 2,446
Summarizes Lease Term and Discount Rate	The following table summarizes the weighted-average remaining lease term and discount rate as of September 30, 2024 and December 31, 2023: September 30, 2024 December 31, 2023 Weighted-average remaining lease term (in years) 1.8 2.4 Weighted-average discount rate 11.0 % 10.9 %

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders of Cullinan (Tables)	9 Months Ended
	Sep. 30, 2024
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 attributable to common stockholders of Cullinan for the three and nine months ended September 30, 2024 and 2023 (in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders of Cullinan $ ( 40,560 ) $ ( 39,183 ) $ ( 119,736 ) $ ( 129,359 ) Denominator: Weighted-average common stock outstanding — basic and diluted 58,337 42,734 52,157 41,130 Net loss per share attributable to common stockholders of Cullinan: Basic and diluted $ ( 0.69 ) $ ( 0.91 ) $ ( 2.30 ) $ ( 3.15 )
Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Income (Loss) Per Share	The following table sets forth potential common shares that were excluded from the computation of diluted net loss per share attributable to common stockholders of Cullinan for the nine months ended September 30, 2024 and 2023 because their effect would have been anti-dilutive (in thousands): Nine Months Ended September 30, 2024 2023 Stock options 8,411 9,355 Preferred stock 6,475 6,024 Restricted stock awards and units 328 158 Employee stock purchase plan 9 1 Total 15,223 15,538

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	4 Months Ended
	Apr. 30, 2024	Apr. 30, 2024	Sep. 30, 2024	Dec. 31, 2023
Nature Of Business And Basis Of Presentation [Line Items]
Cash, cash equivalents, and short-term investments			$ 578,100
Long-term investments and interest receivable			60,900
Short-term investments			$ 475,993	$ 368,633
2024 Private Placement
Nature Of Business And Basis Of Presentation [Line Items]
Net Cash Proceeds from 2024 Private Placement	$ 262,700	$ 262,700
Offering costs	$ 17,300	$ 17,300

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2024 Segment
Accounting Policies [Abstract]
Number of operating segments	1

Reorganization and Reverse Stoc

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, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Stockholders' Equity (Members' Deficit)
Common Stock	$ 6			$ 4
Additional paid-in capital	947,479			654,685
Accumulated other comprehensive income (loss)	970			(129)
Accumulated deficit	(320,593)			(200,857)
Total Cullinan Stockholders' Equity (Members' Deficit)	627,862			453,703
Non-controlling interests in subsidiaries	0			192
Total Stockholders' Equity (Members' Deficit)	$ 627,862	$ 656,221	$ 425,665	$ 453,895	$ 468,817	$ 499,574	$ 485,649	$ 535,029

Financial Instruments - Schedul

Financial Instruments - Schedule of Short-term and Long-term Investment Marketable Securities by Security Type (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	$ 532,999	$ 368,762
Gross Unrealized Gains	1,037	251
Gross Unrealized Losses	(67)	(380)
Estimated Fair Value	533,969	368,633
Long Term Investment
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	57,934
Gross Unrealized Gains	98
Gross Unrealized Losses	(56)
Estimated Fair Value	57,976
Long Term Investment | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	57,934
Gross Unrealized Gains	98
Gross Unrealized Losses	(56)
Estimated Fair Value	57,976
Short Term Investments
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	475,065	368,762
Gross Unrealized Gains	939	251
Gross Unrealized Losses	(11)	(380)
Estimated Fair Value	475,993	368,633
Short Term Investments | U.S. Government Notes
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	227,900	208,289
Gross Unrealized Gains	244	221
Gross Unrealized Losses	(1)	(16)
Estimated Fair Value	228,143	208,494
Short Term Investments | Asset-backed Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	24,932	61,114
Gross Unrealized Gains	55	3
Gross Unrealized Losses	0	(89)
Estimated Fair Value	24,987	61,028
Short Term Investments | Corporate Note Securities
Available For Sale Securities Fair Value To Amortized Cost Basis [Line Items]
Amortized Cost	222,233	99,359
Gross Unrealized Gains	640	27
Gross Unrealized Losses	(10)	(275)
Estimated Fair Value	$ 222,863	$ 99,111

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value of Financial Assets Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	$ 475,993	$ 368,633
Total long-term investments	57,976
Assets Fair Value Disclosure, Total	533,969	368,633
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total long-term investments
Assets Fair Value Disclosure, Total	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	475,993	368,633
Total long-term investments	57,976
Assets Fair Value Disclosure, Total	533,969	368,633
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Total long-term investments
Assets Fair Value Disclosure, Total	0	0
U.S. Government Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	228,143	208,494
U.S. Government Notes | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
U.S. Government Notes | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	228,143	208,494
U.S. Government Notes | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	24,987	61,028
Asset-backed Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Asset-backed Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	24,987	61,028
Asset-backed Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	0	0
Corporate Note Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	222,863	99,111
Total long-term investments	57,976
Corporate Note Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		0
Total long-term investments	0
Corporate Note Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments	222,863	99,111
Total long-term investments	57,976
Corporate Note Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total short-term investments		$ 0
Total long-term investments	$ 0

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Accounts Payable and Accrued Liabilities, Current [Abstract]
Contracted research and development expenses	$ 8,226	$ 8,434
Due to Taiho under collaboration agreement, net	5,026	7,869
Employee compensation	5,870	6,987
Other current liabilities	1,709	914
Total accrued expenses and other current liabilities	$ 20,831	$ 24,204

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
License And Collaboration Agreements [Line Items]
Research and development costs	$ 35,506	$ 33,821	$ 102,411	$ 113,308
General and administrative expense	13,349	10,982	39,460	31,856
Harbour License Agreement
License And Collaboration Agreements [Line Items]
Upfront license fee				25,000
Harbour BioMed US Inc. | Harbour License Agreement
License And Collaboration Agreements [Line Items]
Upfront license fee			$ 25,000
Pearl - Taiho
License And Collaboration Agreements [Line Items]
Percentage of profits from potential sales			50%
Research and development expense related to share of costs		5,400	$ 17,600	15,600
General and administrative expense related to share of costs	6,500
Accrued expenses and other current liabilities	5,000		5,000		$ 7,900
Research and development costs		2,000		5,100
General and administrative expense	700		700
Cullinan [Member]
License And Collaboration Agreements [Line Items]
General and administrative expense	$ 2,200		$ 6,900
Adimab | Collaboration Agreements
License And Collaboration Agreements [Line Items]
Research and development costs		$ 500		500
MIT | Collaboration Agreements
License And Collaboration Agreements [Line Items]
Research and development costs				$ 200

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended				4 Months Ended	9 Months Ended
	Apr. 30, 2024	Sep. 30, 2024	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023	Apr. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	May 31, 2023	Jan. 31, 2023
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Dividends declared		$ 0					$ 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.
Preferred Stock, Par or Stated Value Per Share		$ 0.0001					$ 0.0001		$ 0.0001
Number of shares of common stock, percentage		9.99%					9.99%
Increase in number of shares of preferred stock, percentage		19.99%					19.99%
Shares issued		647,500					647,500		647,500
Shares sold/issued		58,141,130					58,141,130		42,900,083
Losses attributed to noncontrolling interests		$ 0		$ 0			$ (192,000)	$ (179,000)
Biotechnology Value Fund, L.P exchange agreement [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Newly designated Series A preferred stock											600,000
Preferred Stock, Par or Stated Value Per Share											$ 0.0001
Number of common stock exchange											6,500,000
In May 2023
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Offer and sell companys common stock										$ 125,000,000
2024 Private Placement
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Net Cash Proceeds from 2024 Private Placement	$ 262,700,000					$ 262,700,000
Offering costs	$ 17,300,000					$ 17,300,000
Shares sold/issued	14,400,000					14,400,000
Warrants Issued to Purchase Additional Common Shares	300,000					300,000
Common Stock
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Issuance of common stock and pre-funded warrants, Shares			14,421,070
Additional shares issued					3,310,000
Warrant
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Additional shares issued							300,000
Exercise price		$ 0.001					$ 0.001
At-the-Market Equity Offering Program | In May 2023
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Net proceeds							$ 38,400,000
Shares sold/issued		3,300,000					3,300,000
Treasury Stock, Common, Shares		85,600,000					85,600,000
MICA
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Losses attributed to noncontrolling interests							$ 4,400,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Development Subsidiaries and Their Product Candidates (Details) - Subsidiaries [Member]	Sep. 30, 2024	Dec. 31, 2023
Cullinan M I C A Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	99%	95%
Cullinan Florentine Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	97%	96%
Cullinan Amber Corp [Member]
Common Stock And Noncontrolling Interest In Subsidiaries [Line Items]
Subsidiary, Ownership Percentage	94%	94%

Equity-Based Compensation - Sch

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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 9,430	$ 7,740	$ 28,190	$ 22,919
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	5,503	4,536	17,274	13,412
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total equity-based compensation	$ 3,927	$ 3,204	$ 10,916	$ 9,507

Royalty Transfer Agreements - A

Royalty Transfer Agreements - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
Related Party Transaction [Line Items]
Royalties under obligation	$ 0

Commitment and Contingencies (A

Commitment and Contingencies (Additional Information) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Accrued Liabilities	$ 0	$ 0

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2022 ft²	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) ft²	Sep. 30, 2023 USD ($)
Lessee Lease Description [Line Items]
Operating Lease expense		$ 300	$ 400	$ 900	$ 1,300
Operating lease commence date				Feb. 01, 2018
Operating lease expiration date				Jun. 30, 2024
Impairment of long-lived assets				$ 0	$ 440
Sublease Agreement [Member]
Lessee Lease Description [Line Items]
Impairment of long-lived assets				$ 400
Massachusetts
Lessee Lease Description [Line Items]
Operating lease rentable area | ft²	14,000			8,000

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Relating to Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating cash flows from operating leases	$ 1,381	$ 1,378

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments Due Under Operating Lease (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract]
Remainder of 2024	$ 357
2025	1,461
2026	871
Total future minimum lease payments	2,689
Less: imputed interest	(243)
Total lease liabilities at present value	$ 2,446

Leases - Summary of Weighted Av

Leases - Summary of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Sep. 30, 2024	Dec. 31, 2023
Leases [Abstract]
Weighted-average remaining lease term (in years)	1 year 9 months 18 days	2 years 4 months 24 days
Weighted-average discount rate	11%	10.90%

Net Loss per Share Attributab_3

Net Loss per Share Attributable to Common Stockholders of Cullinan - Summary of Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net loss attributable to common stockholders of Cullinan	$ (40,560)	$ (39,183)	$ (119,736)	$ (129,359)
Denominator
Weighted-average common stock outstanding - basic	58,337	42,734	52,157	41,130
Weighted-average common stock outstanding - diluted	58,337	42,734	52,157	41,130
Net loss per share attributable to common stockholders of Cullinan:
Basic	$ (0.69)	$ (0.91)	$ (2.3)	$ (3.15)
Diluted	$ (0.69)	$ (0.91)	$ (2.3)	$ (3.15)

Net Loss per Share Attributab_4

Net Loss per Share Attributable to Common Stockholders of Cullinan - Summary of Outstanding Equity Instruments Excluded from Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	15,223	15,538
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	8,411	9,355
Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	6,475	6,024
Restricted Stock Awards and RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	328	158
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from computation of diluted net loss per share (in shares)	9	1