Theseus Pharmaceuticals (THRX) 10-Q 17 Nov 23 2023 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2023	Nov. 10, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-40869
Entity Registrant Name	THESEUS PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-0712806
Entity Address, Address Line One	314 Main Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	400-9491
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	THRX
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		44,230,135
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Entity Central Index Key	0001745020
Amendment Flag	false
Document Fiscal Period Focus	Q3

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 46,893	$ 94,605
Short-term marketable securities	158,229	103,374
Prepaid expenses and other current assets	4,464	4,137
Total current assets	209,586	202,116
Property and equipment, net	414	416
Operating lease right-of-use asset	3,920	4,334
Long-term marketable securities	20,308	13,817
Other assets	399	1,764
Total assets	234,627	222,447
Current liabilities:
Accounts payable	1,313	4,973
Accrued expenses and other current liabilities	4,931	5,414
Operating lease liability, current portion	759	743
Total current liabilities	7,003	11,130
Operating lease liability, net of current portion	2,897	3,236
Restricted stock liability, net of current portion	205	466
Total liabilities	10,105	14,832
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 50,000,000 shares authorized as of September 30, 2023 and December 31, 2022; 0 shares issued and outstanding as of September 30, 2023 and December 31, 2022	0	0
Common stock, $0.0001 par value; 500,000,000 shares authorized as of September 30, 2023 and December 31, 2022; 43,605,080 and 38,734,446 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	4	4
Additional paid-in capital	379,944	320,183
Accumulated deficit	(155,081)	(112,186)
Accumulated other comprehensive loss	(345)	(386)
Total stockholders’ equity	224,522	207,615
Total liabilities and stockholders’ equity	$ 234,627	$ 222,447

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	43,605,080	38,734,446
Common stock, shares outstanding (in shares)	43,605,080	38,734,446

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 11,519	$ 11,423	$ 36,839	$ 25,315
General and administrative	4,884	4,525	14,206	13,292
Total operating expenses	16,403	15,948	51,045	38,607
Loss from operations	(16,403)	(15,948)	(51,045)	(38,607)
Other income, net	2,899	1,203	8,150	1,716
Total other income, net	2,899	1,203	8,150	1,716
Net loss	(13,504)	(14,745)	(42,895)	(36,891)
Net loss attributable to common stockholders—basic	(13,504)	(14,745)	(42,895)	(36,891)
Net loss attributable to common stockholders—diluted	$ (13,504)	$ (14,745)	$ (42,895)	$ (36,891)
Weighted-average common stock outstanding—basic (in shares)	43,802,221	38,585,980	43,311,740	38,417,993
Weighted-average common stock outstanding—diluted (in shares)	43,802,221	38,585,980	43,311,740	38,417,993
Net loss per share attributable to common stockholders—basic (in usd per share)	$ (0.31)	$ (0.38)	$ (0.99)	$ (0.96)
Net loss per share attributable to common stockholders—diluted (in shares)	$ (0.31)	$ (0.38)	$ (0.99)	$ (0.96)
Comprehensive loss:
Net loss	$ (13,504)	$ (14,745)	$ (42,895)	$ (36,891)
Unrealized gain (loss) on marketable securities	216	(218)	41	(550)
Total comprehensive loss	$ (13,288)	$ (14,963)	$ (42,854)	$ (37,441)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED DEFICIT
Beginning balance (in shares) at Dec. 31, 2021		37,872,604
Beginning balance at Dec. 31, 2021	$ 246,434	$ 4	$ 308,008	$ 0	$ (61,578)
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock (in shares)		85,431
Stock-based compensation	2,044		2,044
Unrealized gain (loss) on marketable securities	(129)			(129)
Net loss	(10,497)				(10,497)
Ending balance (in shares) at Mar. 31, 2022		37,958,035
Ending balance at Mar. 31, 2022	237,852	$ 4	310,052	(129)	(72,075)
Beginning balance (in shares) at Dec. 31, 2021		37,872,604
Beginning balance at Dec. 31, 2021	246,434	$ 4	308,008	0	(61,578)
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities	(550)
Net loss	(36,891)
Ending balance (in shares) at Sep. 30, 2022		38,313,969
Ending balance at Sep. 30, 2022	218,594	$ 4	317,609	(550)	(98,469)
Beginning balance (in shares) at Mar. 31, 2022		37,958,035
Beginning balance at Mar. 31, 2022	237,852	$ 4	310,052	(129)	(72,075)
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock (in shares)		85,431
Stock-based compensation	2,518		2,518
Vesting of early exercised options (in shares)		100,895
Vesting of early exercised options	407		407
Issuance of common stock under employee stock purchase plan (in shares)		10,780
Issuance of common stock under employee stock purchase plan	70		70
Unrealized gain (loss) on marketable securities	(203)			(203)
Net loss	(11,649)				(11,649)
Ending balance (in shares) at Jun. 30, 2022		38,155,141
Ending balance at Jun. 30, 2022	228,995	$ 4	313,047	(332)	(83,724)
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock (in shares)		137,207
Stock-based compensation	4,475		4,475
Vesting of early exercised options (in shares)		21,621
Vesting of early exercised options	87		87
Unrealized gain (loss) on marketable securities	(218)			(218)
Net loss	(14,745)				(14,745)
Ending balance (in shares) at Sep. 30, 2022		38,313,969
Ending balance at Sep. 30, 2022	218,594	$ 4	317,609	(550)	(98,469)
Beginning balance (in shares) at Dec. 31, 2022		38,422,621
Beginning balance at Dec. 31, 2022	207,615	$ 4	320,183	(386)	(112,186)
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock (in shares)		66,015
Stock-based compensation	2,993		2,993
Vesting of early exercised options (in shares)		21,620
Vesting of early exercised options	87		87
Issuance of common stock upon exercise of stock options (in shares)		17,880
Issuance of common stock upon exercise of stock options	48		48
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations (in shares)		7,907
Issuance of common stock, net of issuance costs (in shares)		4,816,301
Issuance of common stock, net of issuance costs of $1,343	49,104		49,104
Unrealized gain (loss) on marketable securities	227			227
Net loss	(14,586)				(14,586)
Ending balance (in shares) at Mar. 31, 2023		43,352,344
Ending balance at Mar. 31, 2023	245,488	$ 4	372,415	(159)	(126,772)
Beginning balance (in shares) at Dec. 31, 2022		38,422,621
Beginning balance at Dec. 31, 2022	$ 207,615	$ 4	320,183	(386)	(112,186)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options (in shares)	17,880
Unrealized gain (loss) on marketable securities	$ 41
Net loss	(42,895)
Ending balance (in shares) at Sep. 30, 2023		43,468,149
Ending balance at Sep. 30, 2023	224,522	$ 4	379,944	(345)	(155,081)
Beginning balance (in shares) at Mar. 31, 2023		43,352,344
Beginning balance at Mar. 31, 2023	245,488	$ 4	372,415	(159)	(126,772)
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock (in shares)		44,017
Stock-based compensation	3,573		3,573
Vesting of early exercised options (in shares)		21,621
Vesting of early exercised options	87		87
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations (in shares)		1,969
Issuance of common stock under employee stock purchase plan (in shares)		24,866
Issuance of common stock under employee stock purchase plan	142		142
Unrealized gain (loss) on marketable securities	(402)			(402)
Net loss	(14,805)				(14,805)
Ending balance (in shares) at Jun. 30, 2023		43,444,817
Ending balance at Jun. 30, 2023	234,083	$ 4	376,217	(561)	(141,577)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	3,640		3,640
Vesting of early exercised options (in shares)		21,621
Vesting of early exercised options	87		87
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations (in shares)		1,711
Unrealized gain (loss) on marketable securities	216			216
Net loss	(13,504)				(13,504)
Ending balance (in shares) at Sep. 30, 2023		43,468,149
Ending balance at Sep. 30, 2023	$ 224,522	$ 4	$ 379,944	$ (345)	$ (155,081)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) $ / shares
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in usd per share) | $ / shares	$ 0.0001
Stock issuance costs | $	$ 1,343

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (42,895,000)	$ (36,891,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	63,369	30,359
Stock-based compensation expense	10,206,000	9,037,000
Amortization and accretion of marketable securities	(3,789,000)	(222,000)
Non-cash interest income	48,000	(23,000)
Non-cash operating lease expense	414,000	256,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(643,000)	746,000
Other assets	1,366,000	1,081,000
Accounts payable	(3,660,000)	818,000
Accrued expenses and other current liabilities	(483,000)	2,762,000
Operating lease liability	(322,000)	(602,000)
Net cash used in operating activities	(39,695,000)	(23,008,000)
Cash flows from investing activities:
Purchases of short-term and long-term marketable securities	(149,684,000)	(155,316,000)
Sales and maturities of short-term and long-term marketable securities	92,120,000	49,600,000
Purchases of property and equipment	(61,000)	(444,000)
Net cash used in investing activities	(57,625,000)	(106,160,000)
Cash flows from financing activities:
Proceeds from issuance of common stock through ATM sales, net of offering costs	49,438,000	0
Proceeds from exercise of stock options	48,000	0
Proceeds from issuance of common stock under employee stock purchase plan	142,000	70,000
Net cash provided by financing activities	49,628,000	70,000
Net increase (decrease) in cash, cash equivalents and restricted cash	(47,692,000)	(129,098,000)
Cash, cash equivalents and restricted cash at beginning of year	94,984,000	245,041,000
Cash, cash equivalents and restricted cash at end of period	47,292,000	115,943,000
Supplemental disclosure of cash flows:
Vesting of early exercised options	261,000	494,000
Obtaining a right-of-use asset in exchange for an operating lease liability	$ 0	$ 4,721,000

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Statement of Cash Flows [Abstract]
Cash and cash equivalents	$ 46,893	$ 115,564
Restricted cash (included in other assets)	399	379
Total cash, cash equivalents, and restricted cash	$ 47,292	$ 115,943

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	Nature of the Business Theseus Pharmaceuticals, Inc. (“Theseus” or the “Company”) is a clinical-stage biopharmaceutical company focused on improving the lives of cancer patients through the discovery, development and commercialization of transformative targeted therapies. The Company was incorporated in December 2017 under the laws of the State of Delaware, and its principal offices are in Cambridge, Massachusetts. Basis of Presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The accompanying condensed consolidated financial statements and footnotes to the condensed consolidated financial statements have been prepared on the same basis as the most recently audited annual consolidated financial statements and, in the opinion of management, reflect all normal recurring adjustments necessary for the fair presentation of the Company’s financial position as of September 30, 2023 and the results of its operations and its cash flows for the interim periods presented. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2022. Liquidity The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. The Company’s product candidate and development programs will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Because of the numerous risks and uncertainties associated with product development, the Company is unable to predict the timing or amount of increased expenses, or when or if the Company will be able to achieve or maintain profitability. Even if the Company is able to generate revenue from product sales, the Company may not become profitable. If the Company fails to become profitable or is unable to sustain profitability on a continuing basis, then the Company may be unable to continue its operations at planned levels and be forced to reduce or terminate its operations. The Company expects to incur substantial operating losses and negative cash flows from operations for the foreseeable future. In accordance with ASC 205-40, Going Concern , the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the condensed consolidated financial statements are issued. As of September 30, 2023, the Company had an accumulated deficit of $155.1 million. During the nine months ended September 30, 2023, the Company incurred a loss of $42.9 million and utilized $39.7 million of cash in operations. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents, and marketable securities of $225.4 million at September 30, 2023 will be sufficient to fund its operating expenses and capital expenditure requirements for at least the next twelve months from issuance of the accompanying condensed consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the accompanying condensed consolidated financial statements are described in the Company’s audited consolidated financial statements, which were included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the Securities and Exchange Commission (“SEC”) on March 9, 2023 (“Annual Report”). There have been no material changes in the Company’s significant accounting policies during the nine months ended September 30, 2023, except as noted below. Unaudited Interim Financial Information The accompanying condensed consolidated financial statements and the accompanying notes as of September 30, 2023 and December 31, 2022 and for the three and nine months ended September 30, 2023 and 2022 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position as of September 30, 2023 and the results of its operations for the three and nine months ended September 30, 2023 and 2022 and its cash flows for the nine months ended September 30, 2023 and 2022. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Estimates and judgments are based on historical information and other market-specific or various relevant assumptions, including in certain circumstances, future projections, that management believes to be reasonable under the circumstances. Actual results could differ materially from estimates. Significant estimates and assumptions are used for, but not limited to, the accruals for research and development expenses. Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and have not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Such deposits have and will continue to exceed federally insured limits. The Company has not experienced any losses on its cash deposits. The Company’s short-term and long-term marketable securities are invested in high grade securities with limited concentration in any one issuer, and as a result, the Company believes represent minimal credit risk. Recently Issued and Adopted Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its condensed consolidated financial statements and disclosures. In June 2016, the FASB issued ASU No. 2016‑13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments , which has been subsequently amended (“ASU 2016‑13”). This updated accounting guidance significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on trade receivables, loans and other financial instruments. This update is effective for the Company’s fiscal year beginning after December 15, 2022, including interim periods within those fiscal years. The Company adopted this new standard on January 1, 2023, and the adoption had no material impact on the Company's consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The carrying values of other current assets, accounts payable, and accrued expenses approximate their fair values due to the short-term nature of these instruments. The Company’s marketable securities, which may include both short-term and long-term marketable securities consisting of high-quality, marketable debt instruments of corporations are measured at fair value in accordance with the fair value hierarchy. A ssets measured at fair value on a recurring basis are as follows (in thousands): FAIR VALUE MEASUREMENTS AT SEPTEMBER 30, 2023 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Cash equivalents: Money market funds $ 43,012 $ — $ — $ 43,012 Marketable securities: Commercial paper — 74,311 — 74,311 Corporate debt securities — 30,095 — 30,095 Asset-backed securities — 23,386 — 23,386 Government securities 19,683 31,062 — 50,745 Total financial assets $ 62,695 $ 158,854 $ — $ 221,549 FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2022 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Cash equivalents: Money market funds $ 6,846 $ — $ — $ 6,846 Commercial paper — 3,989 — 3,989 Marketable securities: Commercial paper — 25,187 — 25,187 Corporate debt securities — 45,673 — 45,673 Asset-backed securities — 13,574 — 13,574 Government securities — 32,757 — 32,757 Total financial assets $ 6,846 $ 121,180 $ — $ 128,026

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities The Company’s investment policy defines allowable investments and establishes guidelines relating to credit quality, diversification, and maturities of its marketable securities to preserve principal and maintain liquidity. In accordance with the Company’s investment policy, it has invested funds in marketable securities as of September 30, 2023 and December 31, 2022 . The Company’s marketable securities are classified as available-for-sale investments. The cost, gross unrealized holding gains, gross unrealized holding losses and fair value of marketable securities by types and classes of security consisted of the following (in thousands): SEPTEMBER 30, 2023 MATURITY AMORTIZED UNREALIZED UNREALIZED FAIR Commercial paper less than 1 $ 74,457 $ — $ (146) $ 74,311 Corporate debt securities less than 1 25,396 2 (49) 25,349 Asset-backed securities less than 1 10,378 — (76) 10,302 Government securities less than 1 48,344 3 (80) 48,267 Short-term marketable securities $ 158,575 $ 5 $ (351) $ 158,229 Corporate debt securities 1 - 2 4,759 — (13) 4,746 Asset-backed securities 1 - 2 13,063 34 (13) 13,084 Government securities 1 - 2 2,485 — (7) 2,478 Long-term marketable securities $ 20,307 $ 34 $ (33) $ 20,308 DECEMBER 31, 2022 MATURITY AMORTIZED UNREALIZED UNREALIZED FAIR Commercial paper less than 1 $ 25,187 $ — $ — $ 25,187 Corporate debt securities less than 1 39,071 9 (185) 38,895 Asset-backed securities less than 1 8,555 2 (10) 8,547 Government securities less than 1 30,892 8 (155) 30,745 Short-term marketable securities $ 103,705 $ 19 $ (350) $ 103,374 Corporate debt securities 1 - 2 6,783 — (5) 6,778 Asset-backed securities 1 - 2 5,074 — (47) 5,027 Government securities 1 - 2 2,015 — (3) 2,012 Long-term marketable securities $ 13,872 $ — $ (55) $ 13,817 The Company has recorded marketable securities at fair value in its condensed consolidated balance sheets and unrealized gains and losses are reported as a component of accumulated other comprehensive income (loss). The amount of realized gains and losses reclassified into earnings are based on the specific identification of the securities sold or securities that reached maturity date. The amount of realized gains and losses reclassified into earnings have not been material to the Company’s condensed consolidated statements of operations. The Company generally does not intend to sell any marketable securities prior to recovery of their amortized cost basis for any marketable securities in an unrealized loss position. The Company has determined that there were no material declines in fair value of its marketable securities due to credit-related factors as of September 30, 2023 and December 31, 2022.

Property and Equipment, net

Property and Equipment, net	9 Months Ended
	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net Property and equipment, net consisted of the following as of September 30, 2023 and as of December 31, 2022 (in thousands): SEPTEMBER 30, DECEMBER 31, Computer equipment $ 50 $ 50 Furniture and fixtures 391 341 Office equipment 87 76 Property and equipment 528 467 Less: accumulated depreciation (114) (51) Property and equipment, net $ 414 $ 416 Depreciation expense for the nine months ended September 30, 2023 and 2022 was $63,369 and $30,359, respectively. There were no impairments recorded to date.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consisted of the following as of September 30, 2023 and as of December 31, 2022 (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued research and development $ 1,235 $ 1,498 Accrued legal 219 164 Accrued compensation and benefits 2,838 3,130 Accrued other 290 273 Restricted stock liability, current 349 349 Total accrued expenses and other current liabilities $ 4,931 $ 5,414

License Agreement

License Agreement	9 Months Ended
	Sep. 30, 2023
License Agreement
License Agreement	License AgreementOn October 27, 2023, the Company provided written notice to ARIAD Pharmaceuticals, Inc. (“ARIAD”) of its termination of the License Agreement, dated June 13, 2018, between the Company and ARIAD (the “ARIAD License Agreement”), which termination will be effective in accordance with the terms of the termination for convenience clause of such agreement. The Company is not subject to any termination penalties related to the termination of the ARIAD License Agreement. For a summary of the terms of the ARIAD License Agreement including the Company’s accounting treatment, please refer to Note 7 to the Company’s audited consolidated financial statements for the year ended December 31, 2022, included in the Company’s Annual Report.

Leases

Leases	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
Leases	Leases The following table presents future lease payments under the terms of the Company’s operating leases as of September 30, 2023, including a reconciliation to the present value of operating lease liabilities recognized in the condensed consolidated balance sheet (in thousands): Fiscal Year Operating Lease Remainder of 2023 $ 195 2024 797 2025 821 2026 846 Thereafter 1,995 Total future minimum lease payments 4,654 Less: imputed interest (998) Present value of lease liabilities $ 3,656

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings The Company may from time to time be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the nine months ended September 30, 2023, and no material legal proceedings are currently pending or, to the best of the Company’s knowledge, threatened. Indemnification Agreements The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to the indemnification agreements, the Company agrees to indemnify, hold harmless, and to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners, in connection with any U.S. patent or any copyright or other intellectual property infringement claim by any third-party with respect to the Company’s products. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. 401(k) Plan The Company maintains a defined-contribution plan under Section 401(k) of the Internal Revenue Code of 1986 (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Matching contributions to the 401(k) Plan may be made at the discretion of management. The Company contributed $0.4 million to the 401(k) Plan during the nine months ended September 30, 2023. There was $0.4 million in employer contributions made to the 401(k) Plan during the year ended December 31, 2022.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock The Company was authorized to issue up to 50,000,000 shares of preferred stock, $0.0001 par value per share, as of September 30, 2023 and December 31, 2022, respectively. There were no shares of preferred stock outstanding as of September 30, 2023 and December 31, 2022, respectively. Common Stock The Company was authorized to issue 500,000,000 shares of common stock, $0.0001 par value per share, as of September 30, 2023 and as of December 31, 2022, respectively. The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preference of the holders of any series of preferred stock. Voting Rights Each share of common stock entitles the holder to one vote on all matters submitted to the stockholders for a vote. Dividends Subject to preferences that may apply to shares of preferred stock outstanding at the time, the holders of outstanding shares of the Company’s common stock are entitled to receive dividends out of funds legally available if and when the Company's board of directors (the "Board"), in its discretion, determines to issue dividends. As of September 30, 2023, no cash dividends have been declared or paid. Liquidation Rights

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation Equity Incentive Plans In September 2021, the Company adopted the Theseus Pharmaceuticals, Inc. 2021 Equity Incentive Plan (the “2021 Plan”), which replaced the 2018 Stock Incentive Plan (the “2018 Plan”) and allows for the issuance of stock options, restricted stock awards, restricted stock units (“RSUs”), and other types of equity awards. No further awards were made under the 2018 Plan as of the effective date of the 2021 Plan. Any options or awards outstanding under the 2018 Plan are governed by their existing terms. On the first day of each fiscal year of the Company during the term of the Plan, commencing on January 1, 2023 and ending on (and including) January 1, 2031, the aggregate number of Common Shares that may be issued under the Plan shall automatically increase by a number equal to the lesser of (a) five percent (5%) of the total number of Common Shares actually issued and outstanding on the last day of the preceding fiscal year, or (b) a number of Common Shares determined by the Board. As of September 30, 2023 and December 31, 2022, the number of shares of common stock reserved for issuance were 11,021,034 and 9,132,930 shares, respectively. Of those shares reserved for issuance, there were 1,972,328 and 1,843,494 shares available for future grant as of September 30, 2023 and December 31, 2022, respectively. The 2021 Plan is administered by the Board (or its compensation committee), and the exercise prices, vesting and other restrictions for the awards are determined at the discretion of the Board, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the common stock on the date of grant. Stock options awarded under the 2021 Plan expire ten years after the grant date unless the Board sets a shorter term. Stock options and restricted stock units granted to employees and non-employees typically vest over four years. Shares of restricted common stock awards granted to employees, officers, members of the Board, advisors, and consultants of the Company typically vest over five years. Certain executives who are option holders are able to early exercise stock option awards prior to full satisfaction of the vesting conditions. If and when this occurs, the executive receives restricted common stock upon exercise of the option, and the shares remain subject to the Company’s right of repurchase, at exercise price, until the remaining vesting terms are met. During the year ended December 31, 2021, options to purchase 345,930 shares of common stock were exercised early. As of September 30, 2023 and December 31, 2022, the Company recognized $0.6 million and $0.8 million, respectively, as a liability related to the early exercise. The amount of remaining unvested shares related to the early exercise as of September 30, 2023 and December 31, 2022 were 136,931 and 201,793 shares, respectively. There were no additional early exercises of options during the nine months ended September 30, 2023. Employee Stock Purchase Plan In September 2021, the Board adopted, and its stockholders approved, the 2021 Employee Stock Purchase Plan (the "ESPP"), which became effective on October 6, 2021. The number of shares of common stock initially reserved for issuance under the ESPP was 400,000. In addition, on the first day of each fiscal year of the Company during the term of the ESPP, commencing on January 1, 2023 and concluding on January 1, 2041, the aggregate number of shares of common stock reserved for issuance under the ESPP shall automatically increase by a number equal to the lesser of (i) one percent (1%) of the total number of shares of common stock actually issued and outstanding on the last day of the preceding fiscal year, and (ii) a number of shares of common stock determined by the Board. The ESPP enables eligible employees to purchase shares of common stock of the Company at the end of each offering period at a price equal to 85% of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant date of purchase. As of September 30, 2023, the number of shares of common stock that may be issued under the ESPP is 730,682. Stock Option Valuation The assumptions that the Company used in Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted are as follows: FOR THE NINE MONTHS ENDED FOR THE YEAR ENDED Risk-free interest rate 3.54% - 4.03% 1.60% - 4.20% Expected term (in years) 5.50 - 6.08 1.03 - 6.08 Expected volatility 87.82% - 89.15% 78.00% - 90.51% Expected dividend yield 0% 0% A summary of option activity under the 2021 Plan during the nine months ended September 30, 2023, is as follows (in thousands except share, per share data and contractual terms): SHARES WEIGHTED-AVERAGE WEIGHTED-AVERAGE AGGREGATE Outstanding as of December 31, 2022 7,257,786 $ 5.95 8.58 $ 10,751 Granted 1,700,130 11.17 Exercised (17,880) 2.70 Forfeited (224,698) 11.37 Expired (1,354) 11.04 Outstanding as of September 30, 2023 8,713,984 $ 6.84 8.06 4,367 Options vested and exercisable as of September 30, 2023 4,135,826 $ 5.03 7.61 $ 3,254 The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The weighted-average per share grant date fair value of options granted during the nine months ended September 30, 2023 and 2022 was $8.44 and $6.80, respectively. As of September 30, 2023, there was $27.8 million of unrecognized stock-based compensation expense related to unvested stock options. The unrecognized stock-based compensation expense is estimated to be recognized over a period of 2.2 years as of September 30, 2023. Restricted Stock Units The Company issues RSUs that generally vest over a four-year period with 25% of the RSUs vesting one year from the vesting commencement date, and the remainder vesting quarterly thereafter over the following 36 months. Any unvested shares underlying an RSU will be forfeited upon termination of services. The fair value of an RSU is equal to the fair market value price of the Company’s common stock on the date of grant. A summary of RSU activity during the nine months ended September 30, 2023 is as follows: SHARES WEIGHTED-AVERAGE Unvested shares at December 31, 2022 31,650 $ 11.21 Granted 333,810 8.88 Forfeited (19,151) 9.21 Vested and released (11,587) 11.21 Unvested shares at September 30, 2023 334,722 $ 9.00 As of September 30, 2023, there was $0.9 million of unrecognized stock-based compensation expense related to unvested RSUs. The unrecognized stock-based compensation expense is estimated to be recognized over a period of 3.2 years as of September 30, 2023. Shares of Restricted Common Stock The Company issued shares of restricted common stock to its founders in May 2018, which vested monthly over five years through May 2023. At issuance, these shares also contained certain performance-based vesting criteria which were associated with the milestone events applicable to the formerly outstanding shares of Series A preferred stock, two of which were achieved in 2020. In conjunction with the termination of the Series A preferred stock purchase agreement, the final performance-based vesting criteria was waived, leaving only service-based vesting criteria remaining for the founders’ shares through the end of the requisite service period. As noted above, certain executives who are option holders are able to early exercise stock option awards prior to full satisfaction of the vesting conditions. If and when such exercise occurs, the executive receives shares of restricted common stock. Early exercise shares are included in the table below. A summary of restricted common stock activity during the nine months ended September 30, 2023 is as follows: SHARES WEIGHTED-AVERAGE Unvested shares at December 31, 2022 311,825 $ 3.96 Vesting of restricted common stock (174,894) 2.63 Unvested shares at September 30, 2023 136,931 $ 5.67 As of September 30, 2023, there was $0.8 million of unrecognized stock-based compensation expense related to unvested restricted common stock. The unrecognized stock-based compensation expense is estimated to be recognized over a period of 1.6 years as of September 30, 2023. Stock-based Compensation Expense Total stock-based compensation expense recorded as research and development and general and administrative expenses, respectively, for employees, directors and non-employees during the three and nine months ended September 30, 2023 and 2022 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Research and development $ 1,855 $ 3,076 $ 5,278 $ 5,362 General and administrative 1,785 1,399 4,928 3,675 $ 3,640 $ 4,475 $ 10,206 $ 9,037

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesIncome taxes for the three and nine months ended September 30, 2023 and 2022 have been calculated based on an estimated annual effective tax rate and certain discrete items. For the three and nine months ended September 30, 2023 and 2022, no income tax was recorded, as the Company recognized losses and maintains a full valuation allowance against its net deferred tax assets. The Company has never been examined by the Internal Revenue Service or any other jurisdiction for any tax years and, as such, all years within the applicable statutes of limitations are potentially subject to audit.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic and diluted loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding (in thousands, except share and per share data): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Numerator: Net loss $ (13,504) $ (14,745) $ (42,895) $ (36,891) Net loss attributable to common stockholders - basic and diluted $ (13,504) $ (14,745) $ (42,895) $ (36,891) Denominator: Weighted-average common stock outstanding - basic and diluted 43,802,221 38,585,980 43,311,740 38,417,993 Net loss per share attributable to common stockholders - basic and diluted $ (0.31) $ (0.38) $ (0.99) $ (0.96) The Company’s potentially dilutive securities, which include preferred stock, unvested restricted common stock, unvested RSUs and stock options, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders for the three and nine months ended September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: SEPTEMBER 30, 2023 2022 Unvested restricted stock 136,931 399,461 Unvested RSUs 334,722 31,650 Options to purchase common stock 8,713,984 7,287,786 9,185,637 7,718,897

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
Subsequent Event	Subsequent EventOn November 13, 2023, the Company announced that it is conducting a process to explore strategic alternatives to maximize shareholder value. In conjunction with this strategic process, the Company also announced a reduction of its workforce by 26 full-time employees, or approximately 72% of the Company’s then-current employee base. The reduction of workforce is expected to result in $5.5 million in severance costs and is expected to be incurred in the fourth quarter of 2023.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited Interim Financial InformationThe accompanying condensed consolidated financial statements and the accompanying notes as of September 30, 2023 and December 31, 2022 and for the three and nine months ended September 30, 2023 and 2022 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position as of September 30, 2023 and the results of its operations for the three and nine months ended September 30, 2023 and 2022 and its cash flows for the nine months ended September 30, 2023 and 2022.
Use of Estimates	Use of EstimatesThe preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Estimates and judgments are based on historical information and other market-specific or various relevant assumptions, including in certain circumstances, future projections, that management believes to be reasonable under the circumstances. Actual results could differ materially from estimates. Significant estimates and assumptions are used for, but not limited to, the accruals for research and development expenses.
Concentration of Credit Risk	Concentration of Credit RiskFinancial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and have not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Such deposits have and will continue to exceed federally insured limits. The Company has not experienced any losses on its cash deposits. The Company’s short-term and long-term marketable securities are invested in high grade securities with limited concentration in any one issuer, and as a result, the Company believes represent minimal credit risk.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its condensed consolidated financial statements and disclosures. In June 2016, the FASB issued ASU No. 2016‑13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments , which has been subsequently amended (“ASU 2016‑13”). This updated accounting guidance significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on trade receivables, loans and other financial instruments. This update is effective for the Company’s fiscal year beginning after December 15, 2022, including interim periods within those fiscal years. The Company adopted this new standard on January 1, 2023, and the adoption had no material impact on the Company's consolidated financial statements.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value on a Recurring Basis	A ssets measured at fair value on a recurring basis are as follows (in thousands): FAIR VALUE MEASUREMENTS AT SEPTEMBER 30, 2023 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Cash equivalents: Money market funds $ 43,012 $ — $ — $ 43,012 Marketable securities: Commercial paper — 74,311 — 74,311 Corporate debt securities — 30,095 — 30,095 Asset-backed securities — 23,386 — 23,386 Government securities 19,683 31,062 — 50,745 Total financial assets $ 62,695 $ 158,854 $ — $ 221,549 FAIR VALUE MEASUREMENTS AT DECEMBER 31, 2022 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Cash equivalents: Money market funds $ 6,846 $ — $ — $ 6,846 Commercial paper — 3,989 — 3,989 Marketable securities: Commercial paper — 25,187 — 25,187 Corporate debt securities — 45,673 — 45,673 Asset-backed securities — 13,574 — 13,574 Government securities — 32,757 — 32,757 Total financial assets $ 6,846 $ 121,180 $ — $ 128,026

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Cost, Gross Unrealized Holding Gains, Gross Unrealized Holding Losses and Fair Value of Marketable Securities by Types and Classes of Security	The cost, gross unrealized holding gains, gross unrealized holding losses and fair value of marketable securities by types and classes of security consisted of the following (in thousands): SEPTEMBER 30, 2023 MATURITY AMORTIZED UNREALIZED UNREALIZED FAIR Commercial paper less than 1 $ 74,457 $ — $ (146) $ 74,311 Corporate debt securities less than 1 25,396 2 (49) 25,349 Asset-backed securities less than 1 10,378 — (76) 10,302 Government securities less than 1 48,344 3 (80) 48,267 Short-term marketable securities $ 158,575 $ 5 $ (351) $ 158,229 Corporate debt securities 1 - 2 4,759 — (13) 4,746 Asset-backed securities 1 - 2 13,063 34 (13) 13,084 Government securities 1 - 2 2,485 — (7) 2,478 Long-term marketable securities $ 20,307 $ 34 $ (33) $ 20,308 DECEMBER 31, 2022 MATURITY AMORTIZED UNREALIZED UNREALIZED FAIR Commercial paper less than 1 $ 25,187 $ — $ — $ 25,187 Corporate debt securities less than 1 39,071 9 (185) 38,895 Asset-backed securities less than 1 8,555 2 (10) 8,547 Government securities less than 1 30,892 8 (155) 30,745 Short-term marketable securities $ 103,705 $ 19 $ (350) $ 103,374 Corporate debt securities 1 - 2 6,783 — (5) 6,778 Asset-backed securities 1 - 2 5,074 — (47) 5,027 Government securities 1 - 2 2,015 — (3) 2,012 Long-term marketable securities $ 13,872 $ — $ (55) $ 13,817

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	9 Months Ended
	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following as of September 30, 2023 and as of December 31, 2022 (in thousands): SEPTEMBER 30, DECEMBER 31, Computer equipment $ 50 $ 50 Furniture and fixtures 391 341 Office equipment 87 76 Property and equipment 528 467 Less: accumulated depreciation (114) (51) Property and equipment, net $ 414 $ 416

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following as of September 30, 2023 and as of December 31, 2022 (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued research and development $ 1,235 $ 1,498 Accrued legal 219 164 Accrued compensation and benefits 2,838 3,130 Accrued other 290 273 Restricted stock liability, current 349 349 Total accrued expenses and other current liabilities $ 4,931 $ 5,414

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
Schedule of Future Lease Payments	The following table presents future lease payments under the terms of the Company’s operating leases as of September 30, 2023, including a reconciliation to the present value of operating lease liabilities recognized in the condensed consolidated balance sheet (in thousands): Fiscal Year Operating Lease Remainder of 2023 $ 195 2024 797 2025 821 2026 846 Thereafter 1,995 Total future minimum lease payments 4,654 Less: imputed interest (998) Present value of lease liabilities $ 3,656

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Stock Option Valuation Assumptions	The assumptions that the Company used in Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted are as follows: FOR THE NINE MONTHS ENDED FOR THE YEAR ENDED Risk-free interest rate 3.54% - 4.03% 1.60% - 4.20% Expected term (in years) 5.50 - 6.08 1.03 - 6.08 Expected volatility 87.82% - 89.15% 78.00% - 90.51% Expected dividend yield 0% 0%
Schedule of Option Activity	A summary of option activity under the 2021 Plan during the nine months ended September 30, 2023, is as follows (in thousands except share, per share data and contractual terms): SHARES WEIGHTED-AVERAGE WEIGHTED-AVERAGE AGGREGATE Outstanding as of December 31, 2022 7,257,786 $ 5.95 8.58 $ 10,751 Granted 1,700,130 11.17 Exercised (17,880) 2.70 Forfeited (224,698) 11.37 Expired (1,354) 11.04 Outstanding as of September 30, 2023 8,713,984 $ 6.84 8.06 4,367 Options vested and exercisable as of September 30, 2023 4,135,826 $ 5.03 7.61 $ 3,254
Schedule of RSU Activity	A summary of RSU activity during the nine months ended September 30, 2023 is as follows: SHARES WEIGHTED-AVERAGE Unvested shares at December 31, 2022 31,650 $ 11.21 Granted 333,810 8.88 Forfeited (19,151) 9.21 Vested and released (11,587) 11.21 Unvested shares at September 30, 2023 334,722 $ 9.00
Schedule of Restricted Common Stock Activity	A summary of restricted common stock activity during the nine months ended September 30, 2023 is as follows: SHARES WEIGHTED-AVERAGE Unvested shares at December 31, 2022 311,825 $ 3.96 Vesting of restricted common stock (174,894) 2.63 Unvested shares at September 30, 2023 136,931 $ 5.67
Schedule of Stock-Based Compensation Expense	Total stock-based compensation expense recorded as research and development and general and administrative expenses, respectively, for employees, directors and non-employees during the three and nine months ended September 30, 2023 and 2022 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Research and development $ 1,855 $ 3,076 $ 5,278 $ 5,362 General and administrative 1,785 1,399 4,928 3,675 $ 3,640 $ 4,475 $ 10,206 $ 9,037

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Loss Per Share	Basic and diluted loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding (in thousands, except share and per share data): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Numerator: Net loss $ (13,504) $ (14,745) $ (42,895) $ (36,891) Net loss attributable to common stockholders - basic and diluted $ (13,504) $ (14,745) $ (42,895) $ (36,891) Denominator: Weighted-average common stock outstanding - basic and diluted 43,802,221 38,585,980 43,311,740 38,417,993 Net loss per share attributable to common stockholders - basic and diluted $ (0.31) $ (0.38) $ (0.99) $ (0.96)
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders for the three and nine months ended September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: SEPTEMBER 30, 2023 2022 Unvested restricted stock 136,931 399,461 Unvested RSUs 334,722 31,650 Options to purchase common stock 8,713,984 7,287,786 9,185,637 7,718,897

Nature of the Business (Details

Nature of the Business (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 155,081						$ 155,081		$ 112,186
Net loss	13,504	$ 14,805	$ 14,586	$ 14,745	$ 11,649	$ 10,497	42,895	$ 36,891
Net cash used in operating activities							39,695	$ 23,008
Amount of cash and cash equivalents, and investments	$ 225,400						$ 225,400

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets
Total financial assets	$ 221,549	$ 128,026
Commercial paper
Assets
Fair value	74,311	25,187
Corporate debt securities
Assets
Fair value	30,095	45,673
Asset-backed securities
Assets
Fair value	23,386	13,574
Government securities
Assets
Fair value	50,745	32,757
Money market funds
Assets
Cash equivalents	43,012	6,846
Commercial paper
Assets
Cash equivalents		3,989
LEVEL 1
Assets
Total financial assets	62,695	6,846
LEVEL 1 | Commercial paper
Assets
Fair value	0	0
LEVEL 1 | Corporate debt securities
Assets
Fair value	0	0
LEVEL 1 | Asset-backed securities
Assets
Fair value	0	0
LEVEL 1 | Government securities
Assets
Fair value	19,683	0
LEVEL 1 | Money market funds
Assets
Cash equivalents	43,012	6,846
LEVEL 1 | Commercial paper
Assets
Cash equivalents		0
LEVEL 2
Assets
Total financial assets	158,854	121,180
LEVEL 2 | Commercial paper
Assets
Fair value	74,311	25,187
LEVEL 2 | Corporate debt securities
Assets
Fair value	30,095	45,673
LEVEL 2 | Asset-backed securities
Assets
Fair value	23,386	13,574
LEVEL 2 | Government securities
Assets
Fair value	31,062	32,757
LEVEL 2 | Money market funds
Assets
Cash equivalents	0	0
LEVEL 2 | Commercial paper
Assets
Cash equivalents		3,989
LEVEL 3
Assets
Total financial assets	0	0
LEVEL 3 | Commercial paper
Assets
Fair value	0	0
LEVEL 3 | Corporate debt securities
Assets
Fair value	0	0
LEVEL 3 | Asset-backed securities
Assets
Fair value	0	0
LEVEL 3 | Government securities
Assets
Fair value	0	0
LEVEL 3 | Money market funds
Assets
Cash equivalents	$ 0	0
LEVEL 3 | Commercial paper
Assets
Cash equivalents		$ 0

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Short-term marketable securities
Investments
AMORTIZED COST	$ 158,575	$ 103,705
UNREALIZED GAIN	5	19
UNREALIZED LOSS	(351)	(350)
FAIR VALUE	158,229	103,374
Long-term marketable securities
Investments
AMORTIZED COST	20,307	13,872
UNREALIZED GAIN	34	0
UNREALIZED LOSS	(33)	(55)
FAIR VALUE	20,308	13,817
Commercial paper | Short-term marketable securities
Investments
AMORTIZED COST	74,457	25,187
UNREALIZED GAIN	0	0
UNREALIZED LOSS	(146)	0
FAIR VALUE	74,311	25,187
Corporate debt securities | Short-term marketable securities
Investments
AMORTIZED COST	25,396	39,071
UNREALIZED GAIN	2	9
UNREALIZED LOSS	(49)	(185)
FAIR VALUE	25,349	38,895
Corporate debt securities | Long-term marketable securities
Investments
AMORTIZED COST	4,759	6,783
UNREALIZED GAIN	0	0
UNREALIZED LOSS	(13)	(5)
FAIR VALUE	4,746	6,778
Asset-backed securities | Short-term marketable securities
Investments
AMORTIZED COST	10,378	8,555
UNREALIZED GAIN	0	2
UNREALIZED LOSS	(76)	(10)
FAIR VALUE	10,302	8,547
Asset-backed securities | Long-term marketable securities
Investments
AMORTIZED COST	13,063	5,074
UNREALIZED GAIN	34	0
UNREALIZED LOSS	(13)	(47)
FAIR VALUE	13,084	5,027
Government securities | Short-term marketable securities
Investments
AMORTIZED COST	48,344	30,892
UNREALIZED GAIN	3	8
UNREALIZED LOSS	(80)	(155)
FAIR VALUE	48,267	30,745
Government securities | Long-term marketable securities
Investments
AMORTIZED COST	2,485	2,015
UNREALIZED GAIN	0	0
UNREALIZED LOSS	(7)	(3)
FAIR VALUE	$ 2,478	$ 2,012

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property and Equipment, net
Property and equipment	$ 528	$ 467
Less: accumulated depreciation	(114)	(51)
Property and equipment, net	414	416
Computer equipment
Property and Equipment, net
Property and equipment	50	50
Furniture and fixtures
Property and Equipment, net
Property and equipment	391	341
Office equipment
Property and Equipment, net
Property and equipment	$ 87	$ 76

Property and Equipment, net - N

Property and Equipment, net - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 63,369	$ 30,359
Impairments recorded to date	$ 0

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued research and development	$ 1,235	$ 1,498
Accrued legal	219	164
Accrued compensation and benefits	2,838	3,130
Accrued other	290	273
Restricted stock liability, current	349	349
Accrued expenses and other current liabilities	$ 4,931	$ 5,414

Leases (Details)

Leases (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Leases [Abstract]
Remainder of 2023	$ 195
2024	797
2025	821
2026	846
Thereafter	1,995
Total future minimum lease payments	4,654
Less: imputed interest	(998)
Present value of lease liabilities	$ 3,656

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
401(k) Plan
Commitments and Contingencies
Amount employer contributions made to the 401(k) plan	$ 0.4	$ 0.4

Stockholders' Equity (Details)

Stockholders' Equity (Details)	9 Months Ended
	Sep. 30, 2023 USD ($) vote $ / shares shares	Jun. 30, 2023 $ / shares	Mar. 31, 2023 $ / shares	Dec. 31, 2022 $ / shares shares	Sep. 30, 2022 $ / shares	Jun. 30, 2022 $ / shares	Mar. 31, 2022 $ / shares	Dec. 31, 2021 $ / shares
Equity [Abstract]
Preferred stock, shares authorized (in shares)	50,000,000			50,000,000
Preferred stock, par value (in usd per share) | $ / shares	$ 0.0001			$ 0.0001
Preferred stock outstanding (in shares)	0			0
Common stock, shares authorized (in shares)	500,000,000			500,000,000
Common stock, par value (in usd per share) | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Number of votes per share of common stock | vote	1
Common stock, cash dividend | $	$ 0

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended		12 Months Ended
	May 31, 2018	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 $ / shares	Dec. 31, 2021 shares	Dec. 31, 2022 USD ($) shares	Sep. 30, 2021 shares
Stock-Based Compensation
Options to purchase common stock, exercised (in shares)		17,880
Weighted-average per share grant date fair value of options granted (in usd per share) | $ / shares		$ 8.44	$ 6.80
Unrecognized stock-based compensation expense related to unvested stock options | $		$ 27.8
Recognition period		1 year 7 months 6 days
Share-Based Payment Arrangement, Option
Stock-Based Compensation
Recognition period		2 years 2 months 12 days
Restricted Stock Units (RSUs)
Stock-Based Compensation
Vesting period		4 years
Unrecognized stock-based compensation expense related to unvested stock options | $		$ 0.9
Recognition period		3 years 2 months 12 days
Restricted Stock Units (RSUs) | Share-Based Payment Arrangement, Tranche One
Stock-Based Compensation
Award vesting rights, percentage		25%
Restricted Stock Units (RSUs) | Share-Based Payment Arrangement, Tranche Two
Stock-Based Compensation
Vesting period		36 months
Restricted Stock
Stock-Based Compensation
Vesting period	5 years
Unrecognized stock-based compensation expense | $		$ 0.8
Employee Stock
Stock-Based Compensation
Annual percentage increase in aggregate number of common stock reserved for issuance		0.01
Shares available for future grant under the Plan (in shares)		730,682
Share-based compensation arrangement by share-based payment award, number of shares authorized						400,000
ESPP, discount from market price, percentage		85%
2021 Plan
Stock-Based Compensation
Annual percentage increase in aggregate number of common stock reserved for issuance		0.05
Shares reserved under the Plan (in shares)		11,021,034			9,132,930
Shares available for future grant under the Plan (in shares)		1,972,328			1,843,494
Expiration period		10 years
Share-based compensation arrangement by share-based payment award, options, liability for early exercise | $		$ 0.6			$ 0.8
2021 Plan | Share-Based Payment Arrangement, Option
Stock-Based Compensation
Vesting period		4 years
2021 Plan | Restricted Stock Units (RSUs)
Stock-Based Compensation
Vesting period		4 years
2021 Plan | Restricted Stock
Stock-Based Compensation
Vesting period		5 years
2021 Plan | Early Exercised Stock Options
Stock-Based Compensation
Options to purchase common stock, exercised (in shares)		0		345,930
Share-based compensation arrangement by share-based payment award, options, nonvested, number of shares		136,931			201,793

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock Option Valuation Assumptions (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Stock-Based Compensation
Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, minimum	3.54%	1.60%
Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, maximum	4.03%	4.20%
Expected volatility, minimum	87.82%	78%
Expected volatility, maximum	89.15%	90.51%
Expected dividend yield	0%	0%
Minimum
Stock-Based Compensation
Expected term (in years)	5 years 6 months	1 year 10 days
Maximum
Stock-Based Compensation
Expected term (in years)	6 years 29 days	6 years 29 days

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
SHARES
Outstanding as of beginning of period (in shares)	7,257,786
Granted (in shares)	1,700,130
Exercised (in shares)	(17,880)
Forfeited (in shares)	(224,698)
Expired (in shares)	(1,354)
Outstanding as of end of period (in shares)	8,713,984	7,257,786
Options vested and exercisable (in shares)	4,135,826
WEIGHTED-AVERAGE PER-SHARE EXERCISE PRICE
Outstanding as of beginning of period (in usd per share)	$ 5.95
Granted (in usd per share)	11.17
Exercised (in usd per share)	2.70
Forfeited (in usd per share)	11.37
Expired (in usd per share)	11.04
Outstanding as of end of period (in usd per share)	6.84	$ 5.95
Options vested and exercisable (in usd per share)	$ 5.03
WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM
Weighted-average remaining contractual term, outstanding	8 years 21 days	8 years 6 months 29 days
Weighted-average remaining contractual term, options vested and exercisable	7 years 7 months 9 days
AGGREGATE INTRINSIC VALUE
Aggregate intrinsic value, outstanding	$ 4,367	$ 10,751
Aggregate intrinsic value, options vested and exercisable	$ 3,254

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of RSU and Restricted Common Stock Activity (Details)	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Restricted Stock Units (RSUs)
SHARES
Unvested shares, beginning balance (in shares) | shares	31,650
Granted (in shares) | shares	333,810
Forfeited (in shares) | shares	(19,151)
Vested and released (in shares) | shares	(11,587)
Unvested shares, ending balance (in shares) | shares	334,722
WEIGHTED-AVERAGE PER-SHARE GRANT-DATE FAIR VALUE
Unvested shares, beginning balance (in usd per share) | $ / shares	$ 11.21
Granted (in usd per share) | $ / shares	8.88
Forfeited (in usd per share) | $ / shares	9.21
Vested and released (in usd per share) | $ / shares	11.21
Unvested shares, ending balance (in usd per share) | $ / shares	$ 9
Restricted Common Stock
SHARES
Unvested shares, beginning balance (in shares) | shares	311,825
Vested and released (in shares) | shares	(174,894)
Unvested shares, ending balance (in shares) | shares	136,931
WEIGHTED-AVERAGE PER-SHARE GRANT-DATE FAIR VALUE
Unvested shares, beginning balance (in usd per share) | $ / shares	$ 3.96
Vested and released (in usd per share) | $ / shares	2.63
Unvested shares, ending balance (in usd per share) | $ / shares	$ 5.67

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Stock-Based Compensation
Stock-based compensation expense	$ 3,640	$ 4,475	$ 10,206	$ 9,037
Research and development
Stock-Based Compensation
Stock-based compensation expense	1,855	3,076	5,278	5,362
General and administrative
Stock-Based Compensation
Stock-based compensation expense	$ 1,785	$ 1,399	$ 4,928	$ 3,675

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income tax	$ 0	$ 0	$ 0	$ 0

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (13,504)	$ (14,805)	$ (14,586)	$ (14,745)	$ (11,649)	$ (10,497)	$ (42,895)	$ (36,891)
Net loss attributable to common stockholders - basic	(13,504)			(14,745)			(42,895)	(36,891)
Net loss attributable to common stockholders - diluted	$ (13,504)			$ (14,745)			$ (42,895)	$ (36,891)
Denominator:
Weighted-average common stock outstanding - basic (in shares)	43,802,221			38,585,980			43,311,740	38,417,993
Weighted-average common stock outstanding - diluted (in shares)	43,802,221			38,585,980			43,311,740	38,417,993
Net loss per share attributable to common stockholders - basic (in usd per share)	$ (0.31)			$ (0.38)			$ (0.99)	$ (0.96)
Net loss per share attributable to common stockholders - diluted (in usd per share)	$ (0.31)			$ (0.38)			$ (0.99)	$ (0.96)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Anti-dilutive Effect
Shares excluded since there inclusion would be anti-dilutive (in shares)	9,185,637	7,718,897
Unvested restricted stock
Anti-dilutive Effect
Shares excluded since there inclusion would be anti-dilutive (in shares)	136,931	399,461
Unvested RSUs
Anti-dilutive Effect
Shares excluded since there inclusion would be anti-dilutive (in shares)	334,722	31,650
Options to purchase common stock
Anti-dilutive Effect
Shares excluded since there inclusion would be anti-dilutive (in shares)	8,713,984	7,287,786

Subsequent Event (Details)

Subsequent Event (Details) - Subsequent Event - Employee Severance $ in Millions	Nov. 13, 2023 USD ($) employee
Subsequent Event [Line Items]
Number of positions expected to be eliminated | employee	26
Number of positions expected to be eliminated, percent	72%
Expected cost | $	$ 5.5