Checkmate Pharmaceuticals (CMPI) 10-Q 13 Nov 20 2020 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Nov. 12, 2020
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Registrant Name	Checkmate Pharmaceuticals, Inc.
Entity Central Index Key	0001651431
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Incorporation, State or Country Code	DE
Entity Address, State or Province	DE
Entity Address, Country	MA
Title of 12(b) Security	Common Stock
Trading Symbol	CMPI
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		21,550,547

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 137,340	$ 4,185
Restricted cash	20	20
Prepaid expenses and other current assets	6,705	921
Total current assets	144,065	5,126
Total assets	144,065	5,126
Current Liabilities:
Accounts payable	3,706	2,234
Accrued expenses	5,154	3,100
Series B preferred stock tranche right liability		300
Total current liabilities	8,860	5,634
Total liabilities	8,860	5,634
Commitments and Contingencies (Note 11)
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount		96,928
Stockholders' Deficit:
Preferred stock, $0.0001 par value, 10,000,000 and 0 shares authorized as of September 30, 2020 and December 31, 2019, respectively; no shares outstanding as of September 30, 2020 and December 31, 2019	0	0
Common stock, $0.0001 par value; 300,000,000 and 76,000,000 shares authorized as of September 30, 2020 and December 31, 2019, respectively; 21,550,547 and 1,488,489 shares issued and outstanding as of September 30, 2020 and December 31, 2019, respectively	2	1
Additional paid-in capital	264,344
Accumulated deficit	(129,141)	(97,437)
Total stockholders' equity (deficit)	135,205	(97,436)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	144,065	5,126
Series A Redeemable Convertible Preferred Stock [Member]
Current Liabilities:
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	0	32,482
Series B Redeemable Convertible Preferred Stock [Member]
Current Liabilities:
Series B preferred stock tranche right liability	300
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	$ 0	$ 64,446

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Temporary equity number of shares issued		51,283,386
Temporary equity number of shares outstanding		51,283,386
Common stock par value per share	$ 0.0001	$ 0.0001
Common stock number of shares authorised	300,000,000	76,000,000
Common stock number of shares issued	21,550,547	1,488,489
Common stock number of shares outstanding	21,550,547	1,488,489
Preferred stock par value per share	$ 0.0001	$ 0.0001
Preferred stock number of shares authorised	10,000,000	0
Preferred stock number of shares outstanding	0	0
Series A Redeemable Convertible Preferred Stock [Member]
Temporary equity par value per share	$ 0.0001	$ 0.0001
Temporary equity number of shares authorised	0	25,000,000
Temporary equity number of shares issued	0	25,000,000
Temporary equity number of shares outstanding	0	25,000,000
Series B Redeemable Convertible Preferred Stock [Member]
Temporary equity par value per share	$ 0.0001	$ 0.0001
Temporary equity number of shares authorised	0	29,972,284
Temporary equity number of shares issued	0	26,283,386
Temporary equity number of shares outstanding	0	26,283,386

Condensed Statements of Operati

Condensed Statements of Operations And Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 6,673	$ 5,076	$ 19,462	$ 17,126
General and administrative	3,160	1,208	6,465	3,365
Total operating expenses	9,833	6,284	25,927	20,491
Loss from operations	(9,833)	(6,284)	(25,927)	(20,491)
Other income (expense), net:
Interest income	4	43	32	160
Change in fair value of convertible loan notes			(83)
Total other income (expense), net	4	43	(51)	160
Net loss and comprehensive loss	(9,829)	(6,241)	(25,978)	(20,331)
Net loss	(9,829)	(6,241)	(25,978)	(20,331)
Accretion of Series B preferred stock tranche right liability		(700)	0	(700)
Accretion of issuance costs on redeemable convertible preferred stock	(5)	(34)	(461)	(85)
Accrued dividends on redeemable convertible preferred stock	(1,579)	(1,573)	(5,536)	(4,301)
Net loss attributable to common stockholders	$ (11,413)	$ (8,548)	$ (31,975)	$ (25,417)
Weighted-average common shares outstanding—basic and diluted	13,580,105	1,486,131	5,519,028	1,438,001
Net loss per share attributable to common stockholders—basic and diluted	$ (0.84)	$ (5.75)	$ (5.79)	$ (17.68)

Condensed Statements of Redeema

Condensed Statements of Redeemable Convertible Preferred Stock And Stockholders' Deficit - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Series A Redeemable Convertible Preferred Stock [Member]	Series A Redeemable Convertible Preferred Stock [Member]Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]Preferred Stock [Member]
Beginning balance at Dec. 31, 2018							$ 30,482		$ 41,491
Beginning balance, shares at Dec. 31, 2018							25,000,000		17,522,259
Beginning balance at Dec. 31, 2018	$ (62,801)		$ 1		$ (62,802)
Beginning balance, shares at Dec. 31, 2018			1,394,961
Issuance of series redeemable convertible preferred, shares									8,761,127
Issuance of series redeemable convertible preferred									$ 18,215
Accretion of issuance costs related to redeemable convertible preferred stock	(85)				(85)				85
Accretion of Series B preferred stock tranche right liability	(700)				(700)			$ 700
Exercise of stock options	74			$ 74
Exercise of stock options, shares			77,876
Exercise of series B preferred stock tranche right	0
Vesting of restricted stock awards, shares			14,189
Stock-based compensation expense	236			236
Accrued dividends on redeemable convertible preferred stock	(4,301)			(310)	(3,991)		$ 1,496		2,805
Net loss	(20,331)				(20,331)
Ending balance at Sep. 30, 2019							$ 31,978		$ 63,296		$ 0
Ending balance, shares at Sep. 30, 2019		0					25,000,000		26,283,386
Ending balance at Sep. 30, 2019	(87,908)		$ 1		(87,909)
Ending balance, shares at Sep. 30, 2019			1,487,026
Beginning balance at Jun. 30, 2019							$ 31,474		$ 54,227
Beginning balance, shares at Jun. 30, 2019							25,000,000		22,594,491
Beginning balance at Jun. 30, 2019	(79,439)		$ 1		(79,440)
Beginning balance, shares at Jun. 30, 2019			1,483,113
Issuance of series redeemable convertible preferred, shares									3,688,895
Issuance of series redeemable convertible preferred									$ 7,266
Accretion of issuance costs related to redeemable convertible preferred stock	(34)				(34)				34		0
Accretion of Series B preferred stock tranche right liability	(700)				(700)			700
Vesting of restricted stock awards, shares			3,913
Stock-based compensation expense	79			79
Accrued dividends on redeemable convertible preferred stock	(1,573)			(79)	(1,494)		$ 504		1,069		0
Net loss	(6,241)				(6,241)
Ending balance at Sep. 30, 2019							$ 31,978		$ 63,296		$ 0
Ending balance, shares at Sep. 30, 2019		0					25,000,000		26,283,386
Ending balance at Sep. 30, 2019	(87,908)		$ 1		(87,909)
Ending balance, shares at Sep. 30, 2019			1,487,026
Beginning balance at Dec. 31, 2019	$ 96,928					$ 32,482	$ 32,482	$ 64,446	$ 64,446
Beginning balance, shares at Dec. 31, 2019	51,283,386					25,000,000	25,000,000	26,283,386	26,283,386
Beginning balance at Dec. 31, 2019	$ (97,436)		$ 1		(97,437)
Beginning balance, shares at Dec. 31, 2019			1,488,489
Issuance of series redeemable convertible preferred, shares									3,688,898		46,828,167
Issuance of series redeemable convertible preferred									$ 7,973		$ 74,566
Conversion of convertible loan notes into redeemable preferred stock	195,847		$ 1	195,846		$ (33,704)		$ (75,898)		$ (86,245)	$ 10,083
Conversion of convertible loan notes into redeemable preferred stock, shares			14,948,241			(25,000,000)		(29,972,284)		(53,123,923)	6,295,756
Accretion of issuance costs related to redeemable convertible preferred stock	(461)				(461)				27		$ 434
Accretion of Series B preferred stock tranche right liability	0
Exercise of stock options	$ 4			4
Exercise of stock options, shares	3,956		3,956
Exercise of series B preferred stock tranche right	$ 300								300
Stock-based compensation expense	1,053			1,053
Accrued dividends on redeemable convertible preferred stock	(5,536)			(271)	(5,265)		$ 1,222		3,152		1,162
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs,shares			5,109,861
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs,value	67,712			67,712
Net loss	(25,978)				(25,978)
Ending balance at Sep. 30, 2020						$ 0	$ 0	$ 0	$ 0		$ 0
Ending balance, shares at Sep. 30, 2020						0	0	0	0		0
Ending balance at Sep. 30, 2020	135,205		$ 2	264,344	(129,141)
Ending balance, shares at Sep. 30, 2020			21,550,547
Beginning balance at Jun. 30, 2020							$ 33,479		$ 75,314		$ 85,475
Beginning balance, shares at Jun. 30, 2020							25,000,000		29,972,284		53,123,923
Beginning balance at Jun. 30, 2020	(117,797)		$ 1		(117,798)
Beginning balance, shares at Jun. 30, 2020			1,488,489
Issuance of series redeemable convertible preferred, shares											0
Issuance of series redeemable convertible preferred											$ (5)
Conversion of convertible loan notes into redeemable preferred stock	195,847		$ 1	195,846			$ (33,704)		$ (75,898)		$ (86,245)
Conversion of convertible loan notes into redeemable preferred stock, shares			14,948,241				(25,000,000)		(29,972,284)		(53,123,923)
Accretion of issuance costs related to redeemable convertible preferred stock	(5)				(5)						$ 5
Exercise of stock options	4			4
Exercise of stock options, shares			3,956
Stock-based compensation expense	852			852
Accrued dividends on redeemable convertible preferred stock	(1,579)			(70)	(1,509)		$ 225		$ 584		770
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs,shares			5,109,861
Issuance of common shares upon initial public offering net of underwriting discounts, commissions and offering costs,value	67,712
Net loss	(9,829)				(9,829)
Ending balance at Sep. 30, 2020						$ 0	$ 0	$ 0	$ 0		$ 0
Ending balance, shares at Sep. 30, 2020						0	0	0	0		0
Ending balance at Sep. 30, 2020	$ 135,205		$ 2	$ 264,344	$ (129,141)
Ending balance, shares at Sep. 30, 2020			21,550,547

Condensed Statements of Redee_2

Condensed Statements of Redeemable Convertible Preferred Stock And Stockholders' Deficit (Parenthetical) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)$ / shares	Sep. 30, 2020USD ($)$ / shares	Sep. 30, 2019USD ($)$ / shares
Series B Redeemable Convertible Preferred Stock [Member]
Shares Issued, Price Per Share | $ / shares	$ 2.1687	$ 2.1687	$ 2.1687
Cash paid for redeemable convertible preferred stock issuance | $	$ 34	$ 27	$ 85
Series C Redeemable Convertible Preferred Stock [Member]
Shares Issued, Price Per Share | $ / shares		$ 1.6016
Cash paid for redeemable convertible preferred stock issuance | $		$ 435

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (25,978)	$ (20,331)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock based compensation	1,053	236
Change in fair value of notes payable	83	0
Change in operating assets and liabilities:
Prepaid expenses and other current assets	(5,784)	(451)
Accounts payable	1,473	781
Accrued expenses	1,735	(499)
Net cash used in operating activities	(27,418)	(20,264)
Cash flows from financing activities
Cash received from stock option exercise	4	74
Proceeds from issuance of convertible preferred stock, net of issuance costs	82,539	18,915
Proceeds from initial public offering of common stock, net of underwriting discounts, commissions and issuance costs	68,030	0
Proceeds from issuance of convertible loan notes	10,000	0
Net cash provided by financing activities	160,573	18,989
Net increase (decrease) in cash, cash equivalents and restricted cash	133,155	(1,275)
Cash, cash equivalents and restricted cash at beginning of period	4,205	12,079
Cash, cash equivalents and restricted cash at end of period	137,360	10,804
Supplemental disclosure of non-cash financing activities:
Accretion of issuance costs to redeemable convertible preferred stock	461	85
Accretion of Series B preferred stock tranche right liability	0	700
Exercise of Series B preferred stock tranche right	300	0
Accrued dividends on redeemable convertible preferred stock	5,536	4,301
Issuance of common stock upon conversion of redeemable convertible preferred stock	195,847	0
Initial public offering issuance costs included in accrued expenses	318	0
Series C Redeemable Convertible Preferred Stock [Member]
Supplemental disclosure of non-cash financing activities:
Conversion of convertible loan notes into series C preferred stock	$ 10,083	$ 0

Nature of Business And Basics o

Nature of Business And Basics of Presentation	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business And Basics of Presentation	1 – N ATURE F USINESS ND ASIS F RESENTATION Nature of Business Checkmate Pharmaceuticals, Inc. (“Checkmate” or the “Company”), headquartered in Cambridge, Massachusetts, is a clinical stage biotechnology company incorporated under the laws of the State of Delaware in July 2015 that is focused on developing and commercializing its proprietary technology to harness the power of the immune system to combat cancer. Since its inception, the Company has devoted substantially all of its efforts to the research and development activities, including recruiting management and technical staff, raising capital, producing materials for non-clinical Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”), and include the accounts of the Company. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company’s significant accounting policies are disclosed in the audited financial statements for the year ended December 31, 2019, included in the Company’s registration statement on Form S-1 No. 333-239932) Initial Public Offering On August 11, 2020, the Company closed the IPO, at which time the Company issued and sold 5,000,000 shares of its common stock, at a price to the public of $15.00 per share. On September 3, 2020, the underwriters of the IPO exercised a portion of their overallotment option by purchasing an additional 109,861 shares from the Company at the IPO price. The Company received approximately $67.7 million in net proceeds, inclusive of the over-allotment exercise and after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In connection with the closing of the IPO, all outstanding shares of the Company’s preferred stock were converted into 14,948,241 shares of common stock. On July 31, 2020, the Company effected a one-for-7.4771 Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, the outcome of clinical trials, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, ability to secure additional capital to fund operations, and risks associated with the COVID-19 As of May 13, 2020, the issuance date of the Company’s audited financial statements for the year ended December 31, 2019, the Company concluded that there was substantial doubt about its ability to continue as a going concern for one year after the date that those financial statements were issued. Subsequent to the issuance of those financial statements, the Company received net proceeds of $67.7 million from the IPO and $75.0 million from the issuance of Series C redeemable convertible preferred stock (“Series C preferred stock”) in June 2020. Accordingly, as of the issuance date of these unaudited condensed financial statements, the Company expects its cash and cash equivalents of $137.3 million as of September 30, 2020 will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months beyond the date of issuance of these unaudited condensed financial statements. The Company may seek additional funding through private or public equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing agreements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Unaudited interim financial information The accompanying interim unaudited condensed financial statements and related disclosures are unaudited and have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q S-X

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2 – S UMMARY F IGNIFICANT CCOUNTING OLICIES The Company’s significant accounting policies are described in Note 3, Summary of Significant Accounting Policies Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process paid-in paid-in-capital During the three months ended September 30, 2020, in connection with the IPO, the Company incurred $1.9 million of additional offering related costs. These costs were recorded as a reduction in additional paid-in-capital Fair Value Option As permitted under ASC 825, Financial Instruments (“ASC 825”), the Company has elected the fair value option to account for its convertible loan notes. In accordance with ASC 825, the Company recorded these convertible loan notes at fair value with changes in fair value recorded as a component of other income (expense), net in the condensed statements of operations and comprehensive loss. As a result of applying the fair value option, direct costs and fees related to the convertible loan notes were expensed as incurred and were not deferred. The Company concluded that it was appropriate to apply the fair value option to the convertible loan notes because there are no non-contingent Recently adopted accounting pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 2018-18”). 2018-18 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”) . 2018-13 2018-13 2018-13 In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception 2017-11”) . 2017-11 2017-11

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurement	3 – F AIR ALUE EASUREMENT The following tables set forth the fair value of the Company’s financial assets and liabilities by level within the fair value hierarchy that are measured at fair value on a recurring basis: September 30, 2020 Level 1 Level 2 Level 3 Total (in thousands) Assets: Money market funds $ 137,100 $ — $ — $ 137,100 Total assets $ 137,100 $ — $ — $ 137,100 December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Assets: Money market funds $ 4,003 $ — $ — $ 4,003 Total assets $ 4,003 $ — $ — $ 4,003 Liabilities: Series B preferred stock tranche right liability $ — $ — $ 300 $ 300 Total liabilities $ — $ — $ 300 $ 300 V ALUATION F ERIES REFERRED TOCK RANCHE IGHT IABILITY The Series B preferred stock tranche right liability at December 31, 2019 is composed of the fair value of rights to purchase Series B redeemable convertible preferred stock (“Series B preferred stock”). The fair value of the Series B preferred stock tranche right liability was determined based on significant inputs not observable in the market, which represent a Level 3 measurement within the fair value hierarchy. The fair value of the preferred stock tranche right liability was determined using a binomial model, which considered as inputs the value of the Series B preferred stock, the expected return of the underlying Series B preferred stock during the period between the valuation date and the expected event date, the probability and timing of achieving the specified milestones as of each valuation date and a discount rate. The most significant assumption in the binomial model impacting the fair value of the Series B preferred stock tranche right liability is the fair value of the Company’s Series B as of each measurement date. The Company determines the fair value per share of the underlying Series B preferred stock by taking into consideration the most recent sales of its Series B preferred stock, results obtained from third-party valuations and additional factors the Company deems relevant. At December 31, 2019, the fair value of each share of Series B preferred stock was $2.20 per share. The series B preferred stock tranche right was exercised on January 14, 2020. The change in fair value of the series B preferred stock tranche right liability from December 31, 2019 to January 14, 2020 was not material. The following table provides a roll-forward of the aggregate fair value of the Company’s series B preferred stock tranche right liability, for which fair value is determined using Level 3 inputs: Series B Preferred (in thousands) Balance as of December 31, 2019 $ 300 Exercise of Series B preferred stock tranche right (300 ) Balance as of September 30, 2020 $ — V ALUATION F ONVERTIBLE OAN OTES The Company elected the fair value option to account for its convertible loan notes issued during April 2020. The fair value of the convertible loan notes was determined based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the initial closing of the Company’s convertible loan notes in April 2020 was determined to be equal to the proceeds of $10.0 million on issuance. The fair value of the convertible loan notes at the time of conversion into the Series C preferred stock in June 2020 was determined to be equal to $1.6016 per share, the value of the Company’s Series C preferred stock into which the convertible loan notes were converted. The change in fair value of the convertible notes prior to close of the Series C preferred stock financing of $0.1 million primarily related to the accrued interest earned on the convertible loan notes prior to such financing. The following table presents a roll-forward of the aggregate fair values of the Company’s convertible loan notes (Note 5) for which fair value is determined by Level 3 inputs: Convertible (in thousands) Balance as of December 31, 2019 Initial fair value $ 10,000 Change in fair value plus accrued interest 83 Settlement of convertible loan notes (10,083 ) Balance as of September 30, 2020 $ —

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Accrued Expenses	4 – A CCRUED XPENSES Accrued expenses consist of the following: September 30, December 31, 2020 2019 (in thousands) Payroll and employee related expenses $ 1,600 $ 1,051 External research and development 3,377 1,969 Other accrued expenses 177 80 Total accrued expenses $ 5,154 $ 3,100

Convertible Loan Notes

Convertible Loan Notes	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Convertible Loan Notes	5 – CONVERTIBLE LOAN NOTES On April 21, 2020, the Company entered into a note purchase agreement (the “note purchase agreement”), pursuant to which the Company issued unsecured convertible loan notes to investors for a total of $10.0 million in principal. The Company will pay simple interest on the outstanding principal amount to the extent not converted at the rate of 8% per annum. No repayment of principal or interest was due until maturity, which occurs 12 months after issuance of the convertible loan notes. Under the note purchase agreement, the convertible loan notes outstanding principal and unpaid accrued interest automatically convert upon a “Qualified Financing” (as defined in the note purchase agreement). If the Qualified Financing is consummated within (i) three months after the date of the agreement, the conversion price shall be equal to 90% of the per share price paid by the investors; (ii) if consummated more than three months after the date of the note purchase agreement, but within six months, the conversion price shall be equal to 80% of the per share price paid by the investors; and (iii) is consummated more than six months after the date of the note purchase agreement, the conversion price shall be equal to 70% of the price per share paid by the investors. On June 2, 2020, upon the Series C preferred stock financing (Note 6), the outstanding principal and unpaid accrued interest of the convertible notes of $10.1 million converted into 6,295,756 shares of Series C preferred stock. Upon execution of the Series C preferred stock, the noteholder investors waived their right to the 90% conversion price and converted the notes at 100% of the per share price paid by the investors in the Qualified Financing. The Company elected the fair value option to account for the convertible loan notes. The Company recorded the convertible loan notes at fair value and subsequently remeasured them to fair value upon settlement of the convertible loan notes. Changes in fair value were recognized as a component of other income (expense), net in the condensed statements of operations and comprehensive loss. The Company recognized a loss in the condensed statements of operations and comprehensive loss of $0.1 million as change in fair value of the convertible notes during the nine months ended September 30, 2020.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	6 – R EDEEMABLE ONVERTIBLE REFERRED TOCK On August 11, 2020, in connection with the closing of the IPO, all outstanding shares of the Company’s preferred stock were converted into 14,948,241 shares of common stock. As a result of the conversion, the Company reclassified the carrying value of its preferred stock, which included all cumulative but unpaid dividends, to common stock and additional paid-in-capital As of December 31, 2019, the preferred stock consisted of the following: Issued and Carrying Liquidation Common (dollars in thousands) Series A redeemable convertible preferred stock 25,000,000 $ 32,482 $ 32,482 3,343,542 Series B redeemable convertible preferred stock 26,283,386 64,446 64,446 3,946,001 51,283,386 $ 96,928 $ 96,928 7,289,543 Preferred stock was classified outside of stockholders’ deficit because the shares contain redemption features that are not solely within the control of the Company. Series C Preferred Stock Financing In June 2020, the Company entered into the Series C Preferred Stock Purchase Agreement, pursuant to which the Company was authorized to issue 62,489,557 shares of Series C preferred stock, at a price of $1.6016 per share. As part of the closing, the Company issued 46,828,167 shares of Series C preferred stock at $1.6016 per share resulting in net proceeds received $74.6 million and an additional 6,295,756 shares of Series C preferred stock in satisfaction of the conversion of $10.0 million convertible loan notes and $0.1 million of accrued interest. The aggregate purchase price of the Series C preferred stock was $85.1 million and the Company incurred issuance costs of $0.4 million, which was recorded as a reduction to the Series C preferred stock carrying value. Series B Preferred Stock Financing In January 2020, the Company issued 3,688,898 of Series B preferred stock at a price of $2.16867 per share, resulting in net proceeds received of $8.0 million. The rights and preferences of the Series B preferred stock issued in January 2020 are identical to Series B preferred stock issued in prior periods. As a result of the issuance, the fair value of the associated outstanding series B tranche right liability of $0.3 million was reclassified to Series B preferred stock. In connection with the Series C preferred stock financing, the conversion price of the Series B preferred stock was decreased from $16.21536 to $14.4451 such that the rate at which shares of Series B preferred stock may be converted into shares of common stock was adjusted from 1:1 to 0.15013:1. Dividends Preferred stock accrued dividends on a cumulative basis at $0.08 per share per annum for Series A redeemable convertible preferred stock (the “Series A preferred stock”) $0.17349 per share per annum for Series B preferred stock and $0.128128 per share per annum for Series C preferred stock, calculated daily and payable when and if declared by the Company’s board of directors. No dividends may be paid to common stockholders until all dividends to preferred stockholders are paid in full, except stock dividends paid to common stockholders. At August 10, 2020, immediately prior to the closing of the IPO, cumulative dividends for Series A preferred stock, Series B preferred stock and Series C preferred stock were $8.7 million, $10.6 million and $1.2 million, respectively. Through September 30, 2020, no dividends have been declared or paid by the Company.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Common Stock	7 – COMMON STOCK The voting, dividend and liquidation rights of the common stockholders are subject to and qualified by the rights, powers and preferences of the preferred stock. The holders of the common stock are entitled to one vote for each share of common stock held at all meetings of stockholders. Common stockholders are entitled to receive dividends declared out of funds legally available, subject to the payment in full of all preferential dividends to which the holders of preferred stock are entitled. In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, after the payment or provision for payment of all debts and liabilities of the Company and all preferential amounts to which the holders of preferred stock are entitled, if any, the common stockholders and preferred stockholders (on an as-converted The Company’s common stock available for future issuance as of September 30, 2020 is summarized as follows: Common stock authorized 300,000,000 Common stock authorized, issued and outstanding 21,550,547 Common stock authorized and reserved for future issuance: Common stock reserved for future exercises of stock option awards 2,491,336 Common stock reserved for future share-based awards 2,512,757 Common stock reserved for issuance under the 2020 ESPP Plan 267,119 Total common stock authorized and reserved for future issuance 26,821,759 Unreserved common stock available for future issuance 273,178,241

Stock based compensation

Stock based compensation	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Stock based compensation	8 – S TOCK ASED OMPENSATION Stock Options In August 2015, the Company’s board of directors approved the Checkmate Pharmaceuticals, Inc. 2015 Stock Option and Grant Plan (the “2015 Plan”), to encourage and enable the officers, employees, directors, consultants and other key persons to acquire a proprietary interest in the Company. The 2015 Plan provided for the granting of incentive stock options, non-statutory In August 2020, the Company’s board of directors and stockholders adopted and approved the Checkmate Pharmaceuticals, Inc. 2020 Stock Option and Incentive Plan (the “2020 Plan”). The 2020 Plan allows for the issuance of stock awards in the form of options, stock appreciation rights, restricted stock awards, restricted stock units, unrestricted stock awards and cash based awards to its officers, employees, non-employee The Company estimates the fair value of stock option awards on the grant date using the Black-Scholes option valuation model with the following weighted-average assumptions: Three and Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.31 % 1.30 % Expected term (in years) 6.05 5.75 Expected volatility 78.3 % 70.0 % Dividend yield — — The per share weighted average grant date fair value of stock options granted during the three and nine months ended September 30, 2020 and 2019 was $14.76 and 1.61 respectively. As of September 30, 2020, total unrecognized compensation expense related to stock options totaled $14.1 million, which is expected to be recognized over a weighted average period of 3.8 years. The following table summarizes the activity under the Company’s stock option plan during the nine months ended September 30, 2020: Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2019 1,073,044 $ 2.45 8.7 $ 902 Granted 1,422,248 $ 14.76 Forfeited — $ — Exercised (3,956 ) $ 0.95 Outstanding at September 30, 2020 2,491,336 $ 9.48 9.1 $ 9,681 Vested and expected to vest at September 30, 2020 2,491,336 $ 9.48 9.1 $ 9,681 Exercisable at September 30, 2020 484,458 $ 2.61 7.4 $ 4,357 The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. The intrinsic value of options exercised during the three and nine months ended September 30, 2020 was $0.1 million. Restricted Stock The Company did not grant restricted stock during the nine months ended September 30, 2020. All previously granted restricted stock was fully vested as of December 31, 2019. Stock-based Compensation Expense Total stock-based compensation expense was classified in the accompanying condensed statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (in thousands) (in thousands) Research and development $ 509 $ 53 $ 588 $ 75 General and administrative 343 26 465 161 Total stock-based compensation expense $ 852 $ 79 $ 1,053 $ 236 Employee Stock Purchase Plan In July 2020, the Company’s board of directors and stockholders adopted and approved the Checkmate Pharmaceuticals, Inc. 2020 Employee Stock Purchase Plan (the “2020 ESPP”) which became effective immediately before the closing of the IPO. The 2020 ESPP was created to provide eligible employees of the Company and other qualified participants to purchase the Company’s common stock at 85% of the fair market value of the common stock on the offering date or the exercise date, whichever is lower, for up to 15% of such employee’s compensation for each pay period. The Company reserved 267,119 shares of common stock for the 2020 ESPP. The 2020 ESPP provides for an annual increase in the number of shares of common stock to be reserved for future issuance under the 2020 ESPP. Each January 1, beginning on January 1, 2022, the number of shares of stock reserved and available for issuance under the 2020 ESPP shall be cumulatively increased by the lesser of (i) 267,119 shares of common stock, (ii) 1% of the number of shares of common stock issued and outstanding on the immediately preceding December 31, or (iii) such lesser number of shares of common stock as determined by the 2020 ESPP administrator.

Income taxes

Income taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income taxes	9 – I NCOME AXES The Company incurred federal and state net operating losses and recorded a full valuation allowance against net deferred tax assets for all periods presented. Accordingly, the Company has not recorded a provision for federal or state income taxes. The Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”), signed into United States law on March 27, 2020 modifies certain provisions of the Tax Cuts and Jobs Act (the “TCJA”) with respect to net operating losses. Under the CARES Act, the limitation on the deduction of net operating losses to 80% of annual taxable income is suspended for taxable years beginning before January 1, 2021. The CARES Act did not have a material impact on the unaudited condensed financial statements.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	10 – NET LOSS PER SHARE Net Loss Per Share Attributable To Common Stockholders Because the Company reports a net loss attributable to common stockholders, basic and diluted net loss per share attributable to common stockholders are the same for both years presented. All preferred stock, unvested restricted stock, and stock options have been excluded from the computation of diluted weighted-average shares outstanding because such securities would have an antidilutive impact. Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator Net loss $ (9,829 ) $ (6,241 ) $ (25,978 ) $ (20,331 ) Accretion of issuance costs on redeemable convertible preferred stock (5 ) (34 ) (461 ) (85 ) Accretion of Series B preferred stock tranche right liability — (700 ) — (700 ) Accrued dividends on redeemable convertible preferred stock (1,579 ) (1,573 ) (5,536 ) (4,301 ) Net loss attributable to common stockholders $ (11,413 ) $ (8,548 ) $ (31,975 ) $ (25,417 ) Denominator: Weighted-average common shares outstanding—basic and diluted 13,580,105 1,486,131 5,519,028 1,438,001 Net loss per share attributable to common stockholders—basic and diluted $ (0.84 ) $ (5.75 ) $ (5.79 ) $ (17.68 ) The following common stock equivalents outstanding at September 30, 2020 and 2019 have been excluded from the calculation of diluted net loss per share because their inclusion would have been antidilutive: September 30, 2020 2019 Options to purchase common stock 2,491,336 946,822 Unvested restricted common stock — 1,463 Redeemable convertible preferred stock — 6,858,727

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	11 – C OMMITMENTS ND ONTINGENCIES Operating Lease The Company has a month-to-month Clinical Trial Collaboration and Supply Agreement On August 22, 2018, the Company entered into the Clinical Trial Collaboration and Supply Agreement (the “CTCSA”) with an affiliate of Merck KgaA (“Merck”) and Pfizer Inc. (“Pfizer” and, together with Merck, the “Alliance”). Pursuant to the CTCSA, the Company and the Alliance will each provide compound drug products that will be dosed concurrently or in combination in a clinical trial sponsored by Pfizer. This agreement was amended on March 4, 2019. In addition to providing a compound drug product to be used in the clinical trial, the Company will reimburse Pfizer for each patient dosed in the study using the Company’s compound at a specified rate outlined in the CTCSA. In no event will the amount of costs due by the Company to Pfizer exceed $4.0 million over the term of the CTCSA. The costs of services performed and material used in connection with the research and development activities of the CTCSA, including reimbursements due to Pfizer, are included in research and development costs and expensed as incurred. The Company incurred $0.3 million and $0.8 million of expense during the three and nine months ended September 30, 2020, respectively, and no expense relating to the Pfizer reimbursement during the three and nine months ended September 30, 2019. License Agreement In June 2015, the Company entered into an exclusive license agreement with Cytos Biotechnology LTD (now Kuros Biosciences AG or “Kuros”) as amended in August 2017 and as further amended in January 2018 (the “Kuros License Agreement”). Pursuant to the Kuros License Agreement, in return for payments made, the Company was granted an exclusive, royalty-bearing, sublicensable, worldwide license, under all of Kuros’ intellectual property rights, including any intellectual property rights arising during the term of the Kuros License Agreement, to commercially develop, manufacture, use, distribute, and sell certain therapeutic products, including CMP-001, CMP-001 CMP-001. As of September 30, 2020, the Company has incurred and paid license fees and milestone payments totaling $2.3 million pursuant to the Kuros License Agreement. These payments are comprised of a license fee of $1.0 million which was recognized in research and development expense in 2015, a $1.0 million milestone payment in connection with the dosing of the first patient in the first Phase 1 clinical trial which was recognized in research and development expense in 2016 and a $0.3 million license amendment fee in connection with the signing of the second amendment to the license agreement which was recognized in research and development expense in 2018. As of September 30, 2020, no other milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized. Other Contingencies During the ordinary course of its operations, the Company may become a party to contractual disputes, litigation, and potential claims. The Company does not believe that the resolution of any of these matters, if any, will have a material adverse effect on its financial position or results of operations.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Nature of Business	Nature of Business Checkmate Pharmaceuticals, Inc. (“Checkmate” or the “Company”), headquartered in Cambridge, Massachusetts, is a clinical stage biotechnology company incorporated under the laws of the State of Delaware in July 2015 that is focused on developing and commercializing its proprietary technology to harness the power of the immune system to combat cancer. Since its inception, the Company has devoted substantially all of its efforts to the research and development activities, including recruiting management and technical staff, raising capital, producing materials for non-clinical
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”), and include the accounts of the Company. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company’s significant accounting policies are disclosed in the audited financial statements for the year ended December 31, 2019, included in the Company’s registration statement on Form S-1 No. 333-239932)
Initial Public Offering	Initial Public Offering On August 11, 2020, the Company closed the IPO, at which time the Company issued and sold 5,000,000 shares of its common stock, at a price to the public of $15.00 per share. On September 3, 2020, the underwriters of the IPO exercised a portion of their overallotment option by purchasing an additional 109,861 shares from the Company at the IPO price. The Company received approximately $67.7 million in net proceeds, inclusive of the over-allotment exercise and after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In connection with the closing of the IPO, all outstanding shares of the Company’s preferred stock were converted into 14,948,241 shares of common stock. On July 31, 2020, the Company effected a one-for-7.4771
Risks and Uncertainties	Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, the outcome of clinical trials, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, ability to secure additional capital to fund operations, and risks associated with the COVID-19 As of May 13, 2020, the issuance date of the Company’s audited financial statements for the year ended December 31, 2019, the Company concluded that there was substantial doubt about its ability to continue as a going concern for one year after the date that those financial statements were issued. Subsequent to the issuance of those financial statements, the Company received net proceeds of $67.7 million from the IPO and $75.0 million from the issuance of Series C redeemable convertible preferred stock (“Series C preferred stock”) in June 2020. Accordingly, as of the issuance date of these unaudited condensed financial statements, the Company expects its cash and cash equivalents of $137.3 million as of September 30, 2020 will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months beyond the date of issuance of these unaudited condensed financial statements. The Company may seek additional funding through private or public equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing agreements. If the Company is unable to obtain additional funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.
Unaudited interim financial information	Unaudited interim financial information The accompanying interim unaudited condensed financial statements and related disclosures are unaudited and have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q S-X
Deferred offering costs	Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process paid-in paid-in-capital During the three months ended September 30, 2020, in connection with the IPO, the Company incurred $1.9 million of additional offering related costs. These costs were recorded as a reduction in additional paid-in-capital
Fair Value Option	Fair Value Option As permitted under ASC 825, Financial Instruments (“ASC 825”), the Company has elected the fair value option to account for its convertible loan notes. In accordance with ASC 825, the Company recorded these convertible loan notes at fair value with changes in fair value recorded as a component of other income (expense), net in the condensed statements of operations and comprehensive loss. As a result of applying the fair value option, direct costs and fees related to the convertible loan notes were expensed as incurred and were not deferred. The Company concluded that it was appropriate to apply the fair value option to the convertible loan notes because there are no non-contingent
Recently adopted accounting pronouncements	Recently adopted accounting pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 2018-18”). 2018-18 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”) . 2018-13 2018-13 2018-13 In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception 2017-11”) . 2017-11 2017-11

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets And Liabilities Measured On Recurring Basis	September 30, 2020 Level 1 Level 2 Level 3 Total (in thousands) Assets: Money market funds $ 137,100 $ — $ — $ 137,100 Total assets $ 137,100 $ — $ — $ 137,100 December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Assets: Money market funds $ 4,003 $ — $ — $ 4,003 Total assets $ 4,003 $ — $ — $ 4,003 Liabilities: Series B preferred stock tranche right liability $ — $ — $ 300 $ 300 Total liabilities $ — $ — $ 300 $ 300
Schedule of Aggregate Fair Value of The Company's Series B Preferred Stock Tranche Right Liability	The following table provides a roll-forward of the aggregate fair value of the Company’s series B preferred stock tranche right liability, for which fair value is determined using Level 3 inputs: Series B Preferred (in thousands) Balance as of December 31, 2019 $ 300 Exercise of Series B preferred stock tranche right (300 ) Balance as of September 30, 2020 $ —
Schedule of Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The following table presents a roll-forward of the aggregate fair values of the Company’s convertible loan notes (Note 5) for which fair value is determined by Level 3 inputs: Convertible (in thousands) Balance as of December 31, 2019 Initial fair value $ 10,000 Change in fair value plus accrued interest 83 Settlement of convertible loan notes (10,083 ) Balance as of September 30, 2020 $ —

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Accrued Expenses	Accrued expenses consist of the following: September 30, December 31, 2020 2019 (in thousands) Payroll and employee related expenses $ 1,600 $ 1,051 External research and development 3,377 1,969 Other accrued expenses 177 80 Total accrued expenses $ 5,154 $ 3,100

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [Abstract]
Schedule of Redeemable Convertible Preferred Stock	As of December 31, 2019, the preferred stock consisted of the following: Issued and Carrying Liquidation Common (dollars in thousands) Series A redeemable convertible preferred stock 25,000,000 $ 32,482 $ 32,482 3,343,542 Series B redeemable convertible preferred stock 26,283,386 64,446 64,446 3,946,001 51,283,386 $ 96,928 $ 96,928 7,289,543

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Summary of Common Stock Available for Future Issuance	The Company’s common stock available for future issuance as of September 30, 2020 is summarized as follows: Common stock authorized 300,000,000 Common stock authorized, issued and outstanding 21,550,547 Common stock authorized and reserved for future issuance: Common stock reserved for future exercises of stock option awards 2,491,336 Common stock reserved for future share-based awards 2,512,757 Common stock reserved for issuance under the 2020 ESPP Plan 267,119 Total common stock authorized and reserved for future issuance 26,821,759 Unreserved common stock available for future issuance 273,178,241

Stock based compensation - (Ta

Stock based compensation - (Tables)	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Schedule of fair value of stock option awards on the grant date using the black-scholes option valuation model	The Company estimates the fair value of stock option awards on the grant date using the Black-Scholes option valuation model with the following weighted-average assumptions: Three and Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.31 % 1.30 % Expected term (in years) 6.05 5.75 Expected volatility 78.3 % 70.0 % Dividend yield — —
Summary of activity under the company's stock option plan	The following table summarizes the activity under the Company’s stock option plan during the nine months ended September 30, 2020: Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2019 1,073,044 $ 2.45 8.7 $ 902 Granted 1,422,248 $ 14.76 Forfeited — $ — Exercised (3,956 ) $ 0.95 Outstanding at September 30, 2020 2,491,336 $ 9.48 9.1 $ 9,681 Vested and expected to vest at September 30, 2020 2,491,336 $ 9.48 9.1 $ 9,681 Exercisable at September 30, 2020 484,458 $ 2.61 7.4 $ 4,357
Summary of total stock-based compensation expense	Total stock-based compensation expense was classified in the accompanying condensed statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (in thousands) (in thousands) Research and development $ 509 $ 53 $ 588 $ 75 General and administrative 343 26 465 161 Total stock-based compensation expense $ 852 $ 79 $ 1,053 $ 236

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Summary of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator Net loss $ (9,829 ) $ (6,241 ) $ (25,978 ) $ (20,331 ) Accretion of issuance costs on redeemable convertible preferred stock (5 ) (34 ) (461 ) (85 ) Accretion of Series B preferred stock tranche right liability — (700 ) — (700 ) Accrued dividends on redeemable convertible preferred stock (1,579 ) (1,573 ) (5,536 ) (4,301 ) Net loss attributable to common stockholders $ (11,413 ) $ (8,548 ) $ (31,975 ) $ (25,417 ) Denominator: Weighted-average common shares outstanding—basic and diluted 13,580,105 1,486,131 5,519,028 1,438,001 Net loss per share attributable to common stockholders—basic and diluted $ (0.84 ) $ (5.75 ) $ (5.79 ) $ (17.68 )
Summary of Potentially Dilutive Shares Excluded From The Calculation of Diluted Net Loss	The following common stock equivalents outstanding at September 30, 2020 and 2019 have been excluded from the calculation of diluted net loss per share because their inclusion would have been antidilutive: September 30, 2020 2019 Options to purchase common stock 2,491,336 946,822 Unvested restricted common stock — 1,463 Redeemable convertible preferred stock — 6,858,727

Nature of Business And Basics_2

Nature of Business And Basics of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands	Sep. 03, 2020shares	Aug. 31, 2020USD ($)	Aug. 11, 2020USD ($)$ / sharesshares	Jul. 31, 2020	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Subsidiary, Sale of Stock [Line Items]
Proceeds from initial public offering of common stock, net of underwriting discounts, commissions and issuance costs			$ 67,700			$ 68,030	$ 0
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs						195,847	$ 0
Cash and cash equivalents					$ 137,340	$ 137,340		$ 4,185
Series C Redeemable Convertible Preferred Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Shares Issued, Price Per Share | $ / shares					$ 1.6016	$ 1.6016
Proceeds from initial public offering gross						$ 75,000
Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Shares Issued During Period | shares					5,109,861	5,109,861
Reverse stock split, conversion ratio				7.4771
Description of the reverse stock split arrangement				On July 31, 2020, the Company effected a one-for-7.4771 reverse stock split of its common stock. Upon the effectiveness of the reverse stock split, (i) all shares of outstanding common stock were adjusted; (ii) the number of shares of common stock for which each outstanding option to purchase common stock is exercisable were adjusted; and (iii) the exercise price of each outstanding option to purchase common stock was adjusted. All of the outstanding common stock share numbers (including shares of common stock subject to the Company’s options and as converted for the outstanding convertible preferred stock shares), share prices, exercise prices and per share amounts contained in the interim unaudited condensed financial statements have been retroactively adjusted in the interim condensed financial statements to reflect this reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock were not adjusted as a result of the reverse stock split. The reverse stock split resulted in an adjustment to the redeemable convertible preferred stock conversion prices to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion.
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		$ 67,700
Convertible Preferred Stock, Shares Issued upon Conversion | shares			14,948,241
IPO [Member] | Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Shares Issued During Period | shares			5,000,000
Shares Issued, Price Per Share | $ / shares			$ 15
Over-Allotment Option [Member] | Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Shares Issued During Period | shares	109,861

Summary of Significant Accoun_3

Summary of Significant Accounting Policies -Additional Information (Detail) $ in Millions	3 Months Ended
	Sep. 30, 2020USD ($)
Accounting Policies [Abstract]
Deferred offering costs reclassified to additional paid-in-capita	$ 1.6
Payments Of Stock Issuance Costs	$ 1.9

Fair Value Measurement - Schedu

Fair Value Measurement - Schedule of Fair Value Assets And Liabilities Measured On Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Assets, Fair Value Disclosure	$ 137,100	$ 4,003
Liabilities:
Financial Liabilities Fair Value Disclosure		300
Money Market Funds [Member]
Assets:
Assets, Fair Value Disclosure	137,100	4,003
Series B Preferred Stock Tranche Right Liability [Member]
Liabilities:
Financial Liabilities Fair Value Disclosure		300
Fair Value, Inputs, Level 1 [Member]
Assets:
Assets, Fair Value Disclosure	137,100	4,003
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Assets, Fair Value Disclosure	$ 137,100	4,003
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Financial Liabilities Fair Value Disclosure		300
Fair Value, Inputs, Level 3 [Member] | Series B Preferred Stock Tranche Right Liability [Member]
Liabilities:
Financial Liabilities Fair Value Disclosure		$ 300

Fair Value Measurement - Sche_2

Fair Value Measurement - Schedule of Aggregate Fair Value of The Company's Series B Preferred Stock Tranche Right Liability (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Aggregate fair value of the Companys series B preferred stock tranche right liability [Line Items]
Balance as of December 31, 2019	$ 300
Exercise of series B preferred stock tranche right	300	$ 0
Series B Redeemable Convertible Preferred Stock [Member]
Schedule Of Aggregate fair value of the Companys series B preferred stock tranche right liability [Line Items]
Balance as of June 30, 2020	300
Series B Redeemable Convertible Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule Of Aggregate fair value of the Companys series B preferred stock tranche right liability [Line Items]
Balance as of December 31, 2019	300
Exercise of series B preferred stock tranche right	(300)
Balance as of June 30, 2020	$ 0

Fair Value Measurement - Sche_3

Fair Value Measurement - Schedule of Fair Value, Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Initial fair value	$ 10,000	$ 0
Convertible Notes Payable [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Initial fair value	10,000
Change in fair value plus accrued interest	83
Settlement of convertible loan notes	(10,083)
Ending balance	$ 0

Fair Value Measurement - Additi

Fair Value Measurement - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Apr. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Apr. 01, 2020
Fair Value Disclosures [Line Items]
Proceeds from convertible loan notes			$ 10,000	$ 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Disclosures [Line Items]
Proceeds from convertible loan notes		$ 10,000
Series B Redeemable Convertible Preferred Stock [Member]
Fair Value Disclosures [Line Items]
Fair value per share			$ 2.20
Exercise date of preferred stock tranche right	Jan. 14, 2020
Series C Redeemable Convertible Preferred Stock [Member]
Fair Value Disclosures [Line Items]
Debt instrument conversion price					$ 1.6016
Series C Redeemable Convertible Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Disclosures [Line Items]
Change in fair value of convertible notes			$ 100

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Payroll and employee related expenses	$ 1,600	$ 1,051
External research and development	3,377	1,969
Other accrued expenses	177	80
Total accrued expenses	$ 5,154	$ 3,100

Convertible Loan Notes - Additi

Convertible Loan Notes - Additional Information (Detail) - USD ($) $ in Millions	Jun. 02, 2020	Jun. 30, 2020	Sep. 30, 2020	Apr. 30, 2020	Apr. 21, 2020
Convertible Notes Payable [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt Face Amount					$ 10
Debt Instrument Interest Rate				8.00%
Convertible Notes Payable [Member] | Fair Value, Inputs, Level 3 [Member]
Disclosure of Convertible Loan Notes [Line Items]
Gain loss on change in fair value of convertible notes			$ 0.1
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage One [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt instrument conversion price as a percentage of share price			90.00%
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage One [Member] | Qualified Financing Period One [Member] | Maximum [Member]
Disclosure of Convertible Loan Notes [Line Items]
Term of qualified financing from the date of agreement for conversion price eligibility		3 months
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage Two [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt instrument conversion price as a percentage of share price			80.00%
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage Two [Member] | Qualified Financing Period Two [Member] | Maximum [Member]
Disclosure of Convertible Loan Notes [Line Items]
Term of qualified financing from the date of agreement for conversion price eligibility		6 months
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage Two [Member] | Qualified Financing Period Two [Member] | Minimum [Member]
Disclosure of Convertible Loan Notes [Line Items]
Term of qualified financing from the date of agreement for conversion price eligibility		3 months
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage Three [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt instrument conversion price as a percentage of share price			70.00%
Convertible Notes Payable [Member] | Debt Instrument Conversion Price Percentage Three [Member] | Qualified Financing Period Three [Member]
Disclosure of Convertible Loan Notes [Line Items]
Term of qualified financing from the date of agreement for conversion price eligibility		6 months
Series C Redeemable Convertible Preferred Stock [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt conversion, shares issued			6,295,756
Series C Redeemable Convertible Preferred Stock [Member] | Convertible Notes Payable [Member]
Disclosure of Convertible Loan Notes [Line Items]
Debt Instrument benenficial conversion feature	$ 10.1
Conversion price as a percentage of share price waived	90.00%
Conversion price as a percentage of share price into which the debt instrument is converted	100.00%

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Aug. 11, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Temporary equity number of shares issued			51,283,386
Temporary equity number of shares outstanding		0	51,283,386
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount			$ 96,928
Temporary equity liquidation preference			$ 96,928
Common stock issuable upon conversion			7,289,543
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity number of shares issued	0		25,000,000
Temporary equity number of shares outstanding	0		25,000,000
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	$ 0		$ 32,482
Temporary equity liquidation preference			$ 32,482
Common stock issuable upon conversion			3,343,542
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity number of shares issued	0		26,283,386
Temporary equity number of shares outstanding	0		26,283,386
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	$ 0		$ 64,446
Temporary equity liquidation preference			$ 64,446
Common stock issuable upon conversion			3,946,001

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Stock - Additional Information (Detail)	Aug. 31, 2020USD ($)	Aug. 11, 2020USD ($)shares	Aug. 10, 2020USD ($)	Jun. 30, 2020USD ($)$ / sharesshares	Jan. 31, 2020$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)shares
Temporary Equity [Line Items]
Gross Proceeds from temporary equity								$ 195,847,000	$ 0
Preferred stock tranche right liability current										$ 300,000
Temporary equity, shares outstanding | shares		0								51,283,386
Accrued dividends on redeemable convertible preferred stock						$ 1,579,000	$ 1,573,000	5,536,000	4,301,000
Common Stock [Member]
Temporary Equity [Line Items]
Gross Proceeds from temporary equity	$ 67,700,000
Convertible Preferred Stock, Shares Issued upon Conversion | shares		14,948,241
Accrued dividends on redeemable convertible preferred stock		$ 1,000,000
Additional Paid-in Capital [Member]
Temporary Equity [Line Items]
Accrued dividends on redeemable convertible preferred stock		$ 195,800,000				$ 70,000	$ 79,000	$ 271,000	$ 310,000
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock per share amount of cumulative dividend | $ / shares								$ 0.08
Preferred stock dividend declared								$ 0
Temporary equity shares authorised | shares						0		0		25,000,000
Temporary equity, shares outstanding | shares						0		0		25,000,000
Preferred stock amount of cumulative dividend			$ 8,700,000
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity issue price per share | $ / shares					$ 2.16867
Net proceeds from temporary equity				$ 8,000,000
Preferred stock per share amount of cumulative dividend | $ / shares								$ 0.17349
Preferred stock dividend declared								$ 0
Preferred stock tranche right liability current						$ 300,000		$ 300,000
Temporary equity shares authorised | shares						0		0		29,972,284
Temporary equity, shares outstanding | shares						0		0		26,283,386
Temporary equity shares issued during the period | shares					3,688,898
Preferred stock amount of cumulative dividend			10,600,000
Series B Redeemable Convertible Preferred Stock [Member] | Conversion Ratio One [Member]
Temporary Equity [Line Items]
Conversion ratio of redeemable covertible preferred stock into common stock						1		1
Series B Redeemable Convertible Preferred Stock [Member] | Conversion Ratio Two [Member]
Temporary Equity [Line Items]
Conversion ratio of redeemable covertible preferred stock into common stock						0.15013		0.15013
Series B Redeemable Convertible Preferred Stock [Member] | Conversion Price One [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock conversion price | $ / shares						$ 16.21536		$ 16.21536
Series B Redeemable Convertible Preferred Stock [Member] | Conversion Price Two [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock conversion price | $ / shares						$ 14.4451		14.4451
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity issue price per share | $ / shares				$ 1.6016
Preferred stock per share amount of cumulative dividend | $ / shares								$ 0.128128
Preferred stock dividend declared								$ 0
Preferred stock amount of cumulative dividend			$ 1,200,000
Series C Redeemable Convertible Preferred Stock [Member] | Series C Preferred Stock Purchase Agreement [Member]
Temporary Equity [Line Items]
Temporary equity issue price per share | $ / shares				$ 1.6016
Gross Proceeds from temporary equity								$ 74,600,000
Temporary equity shares authorised | shares				62,489,557
Temporary equity shares issued during the period | shares				46,828,167
Temporary equity unamortised stock issuance costs				$ 400,000
Series C Redeemable Convertible Preferred Stock [Member] | Series C Preferred Stock Purchase Agreement [Member] | Convertible Notes Payable [Member] | Unsecured Debt [Member]
Temporary Equity [Line Items]
Temporary equity shares issued during the period | shares								6,295,756
Debt instrument converted value In excess of principal								$ 100,000
Debt conversion original debt amount				10,000,000
Temporary equity shares issued during the period				$ 85,100,000
Undesignated Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity shares authorised | shares		10,000,000

Common Stock - Summary of Commo

Common Stock - Summary of Common Stock Available for Future Issuance (Detail) - shares	Sep. 30, 2020	Dec. 31, 2019
Disclosure of Common Stock Summary of Outstanding and Reserved for Future Issuance [Line Items]
Common stock authorized	300,000,000	76,000,000
Common stock issued	21,550,547	1,488,489
Common stock outstanding	21,550,547	1,488,489
Common stock authorized and reserved for future issuance		7,289,543
Total common stock authorized and reserved for future issuance	26,821,759
Unreserved common stock available for future issuance	273,178,241
Employee Stock Option [Member]
Disclosure of Common Stock Summary of Outstanding and Reserved for Future Issuance [Line Items]
Common stock authorized and reserved for future issuance	2,491,336
Share-based Payment Arrangement [Member]
Disclosure of Common Stock Summary of Outstanding and Reserved for Future Issuance [Line Items]
Common stock authorized and reserved for future issuance	2,512,757
2020 Employee Stock Purchase Plan [Member]
Disclosure of Common Stock Summary of Outstanding and Reserved for Future Issuance [Line Items]
Common stock authorized and reserved for future issuance	267,119

Stock based compensation - Sche

Stock based compensation - Schedule of fair value of stock option awards on the grant date using the Black-Scholes option valuation model (Detail)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate	0.31%	1.30%
Expected term (in years)	6 years 18 days	5 years 9 months
Expected volatility	78.30%	70.00%
Dividend yield	0.00%	0.00%

Stock based compensation - Summ

Stock based compensation - Summary the activity under the Company's stock option plan (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Share-based Payment Arrangement [Abstract]
Outstanding Number, Beginning balance | shares	1,073,044
Outstanding Number, Granted | shares	1,422,248
Outstanding Number, Forfeited | shares	0
Outstanding Number ,Exercised | shares	(3,956)
Outstanding Number , Ending balance | shares	2,491,336	1,073,044
Outstanding Number, Vested and expected to vest | shares	2,491,336
Outstanding Number, Exercisable | shares	484,458
Weighted Average Exercise price, Beginning balance | $ / shares	$ 2.45
Weighted Average Exercise price, Granted | $ / shares	14.76
Weighted Average Exercise price, Forfeited | $ / shares	0
Weighted Average Exercise price, Exercised | $ / shares	0.95
Weighted Average Exercise price, Ending balance | $ / shares	9.48	$ 2.45
Weighted Average Exercise price, Vested and expected to vest | $ / shares	9.48
Weighted Average Exercise price, Exercisable | $ / shares	$ 2.61
Weighted-Average Remaining Contractual Term	9 years 1 month 6 days	8 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	9 years 1 month 6 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 4 months 24 days
Aggregate Intrinsic Value | $	$ 9,681	$ 902
Aggregate Intrinsic Value, Vested and expected to vest | $	9,681	$ 902
Aggregate Intrinsic Value, Exercisable | $	$ 4,357

Stock based compensation - Su_2

Stock based compensation - Summary of total stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 852	$ 79	$ 1,053	$ 236
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	509	53	588	75
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 343	$ 26	$ 465	$ 161

Stock based compensation - Addi

Stock based compensation - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2021	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2020	Aug. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance under 2015 plan							7,289,543
Options exercised				3,956
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU's granted				0
RSU's vested				0
2020 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance under 2015 plan			267,119	267,119
Share-based Payment Award, Percentage of Outstanding Stock Maximum		1.00%
2015 Stock Option and Grant Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Award, Number of Shares Available for Issuance						729,575
Unrecognized compensation expense related to stock option			$ 14.1	$ 14.1
Unrecognized compensation expense expected to be recognized, Weighted average period				3 years 9 months 18 days
Options exercised			100,000	100,000
Weighted average grant date fair value of stock options granted, fair value			$ 14.76	$ 1.61
2020 Stock Option and Grant Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Award, Number of Shares Available for Issuance						3,205,430
Discount on purchase		85.00%
Shares of common stock reserved for issuance under 2015 plan		267,119
Maximum [Member] | 2020 Stock Option and Grant Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount on purchase		15.00%
Share-based Payment Award, Number of Shares Authorized for Issuance			3,935,005	3,935,005
Subsequent Event [Member] | 2020 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance under 2015 plan					267,119
Subsequent Event [Member] | 2020 Stock Option and Grant Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Award, Percentage of Outstanding Stock Maximum	4.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020
Taxable Years Beginning After January 2021 [Member]
Income Tax Disclosure [Line Items]
Percentage of net operating losses eligible for deduction	80.00%

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss	$ (9,829)	$ (6,241)	$ (25,978)	$ (20,331)
Accretion of issuance costs related to redeemable convertible preferred stock	(5)	(34)	(461)	(85)
Accretion of Series B preferred stock tranche right liability		(700)	0	(700)
Accrued dividends on redeemable convertible preferred stock	(1,579)	(1,573)	(5,536)	(4,301)
Net loss attributable to common stockholders	$ (11,413)	$ (8,548)	$ (31,975)	$ (25,417)
Weighted-average common shares outstanding—basic and diluted	13,580,105	1,486,131	5,519,028	1,438,001
Net loss per share attributable to common stockholders—basic and diluted	$ (0.84)	$ (5.75)	$ (5.79)	$ (17.68)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Potentially Dilutive Shares Excluded From The Calculation of Diluted Net Loss (Detail) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,491,336	946,822
Unvested restricted common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		1,463
Redeemable convertible preferred stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		6,858,727

Commitments And Contingencies -

Commitments And Contingencies - Additional information (Detail) - USD ($) $ in Thousands	Mar. 04, 2019	Jun. 30, 2015	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2016	Sep. 30, 2015
Long-term Purchase Commitment [Line Items]
Research and development expenses recognised			$ 6,673	$ 5,076	$ 19,462	$ 17,126
Operating lease rental expenses			100	$ 100	400	$ 300
CTSA Agreement [Member] | Research and Development Arrangement [Member]
Long-term Purchase Commitment [Line Items]
CTCSA agreement, commitment amount	$ 4,000
Research and development costs and expenses Incurred			300		800
Kuros Agreement commitment amount	$ 4,000
CTSA Agreement [Member] | Research and Development Arrangement [Member] | Pfizer [Member]
Long-term Purchase Commitment [Line Items]
Research and development costs and expenses Incurred			$ 0		0
Kuros License Agreement [Member]
Long-term Purchase Commitment [Line Items]
CTCSA agreement, commitment amount		$ 56,000
Kuros Agreement commitment amount		56,000
Milestone Payments Paid									$ 2,300
Kuros License Agreement [Member] | Phase one Trail [Member]
Long-term Purchase Commitment [Line Items]
CTCSA agreement, commitment amount		2,000
Kuros Agreement commitment amount		2,000
Kuros License Agreement [Member] | Phase Two Trial [Member]
Long-term Purchase Commitment [Line Items]
CTCSA agreement, commitment amount		4,000
Kuros Agreement commitment amount		$ 4,000
Kuros License Agreement [Member] | License [Member]
Long-term Purchase Commitment [Line Items]
Research and development expenses recognised									$ 1,000
Kuros License Agreement [Member] | Technology Service [Member] | Phase one Trail [Member]
Long-term Purchase Commitment [Line Items]
Research and development expenses recognised								$ 1,000
Kuros License Second Amendment Agreement [Member]
Long-term Purchase Commitment [Line Items]
Research and development expenses recognised					$ 0
Kuros License Second Amendment Agreement [Member] | License [Member]
Long-term Purchase Commitment [Line Items]
Research and development expenses recognised							$ 300