Oncorus (ONCR) S-1 9 Feb 21 IPO registration Financial data

Cover Page

Cover Page	9 Months Ended
	Sep. 30, 2020
Cover [Abstract]
Document Type	S-1
Amendment Flag	false
Entity Registrant Name	Oncorus, Inc.
Entity Central Index Key	0001671818
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 54,019	$ 45,286	$ 20,079
Prepaid expenses and other current assets	1,577	615	827
Total current assets	55,596	45,901	20,906
Property and equipment, net	4,506	4,475	4,300
Deferred offering costs	1,507
Other assets	450	450	450
Total assets	62,059	50,826	25,656
Current liabilities:
Accounts payable	1,470	942	975
Accrued expenses	3,155	3,521	1,290
Deferred rent	500	467	423
Other current liabilities	8	8	8
Total current liabilities	5,133	4,938	2,696
Series B tranche rights (Note 5)		1,876
Deferred rent, net of current portion	1,295	1,677	2,144
Total liabilities	6,428	8,491	4,840
Commitments and contingencies (Note 9)
Redeemable convertible preferred stock:
Redeemable convertible preferred stock
Stockholders' deficit:
Common stock, $0.0001 par value, 227,000 shares authorized; 1,072 and 989 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively
Additional paid-in capital			906
Accumulated deficit	(118,257)	(74,297)	(40,983)
Total stockholders' deficit	(118,257)	(74,297)	(40,077)
Total liabilities, redeemable convertible preferred stock and stockholders' deficit	62,059	50,826	25,656
Series A-1 redeemable convertible preferred stock [Member]
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	68,220	63,494	$ 60,893
Series B redeemable convertible preferred stock [Member]
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	$ 105,668	$ 53,138

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Common Stock, Par or Stated Value Per Share	$ 0.0001	$ 0.0001	$ 0.0001
Common Stock, Shares Authorized	227,000,000	227,000,000	107,000,000
Common Stock, Shares Issued	1,072,000	989,000	881,000
Common Stock, Shares Outstanding	1,072,000	989,000	881,000
Series A-1 redeemable convertible preferred stock [Member]
Temporary Equity, Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Temporary Equity, Shares Authorized	76,500,000	76,500,000	77,000,000
Temporary Equity, Shares Issued	76,500,000	76,500,000	76,500,000
Temporary Equity, Shares Outstanding	76,499,992	76,499,992	76,499,992
Temporary Equity, Liquidation Preference	$ 68,436	$ 63,739	$ 63,739
Series B redeemable convertible preferred stock [Member]
Temporary Equity, Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Temporary Equity, Shares Authorized	104,225,000	104,225,000	0
Temporary Equity, Shares Issued	104,225,000	62,535,000	0
Temporary Equity, Shares Outstanding	104,225,000	62,535,000	0
Temporary Equity, Liquidation Preference	$ 94,492	$ 55,326	$ 55,326

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 6,927	$ 6,221	$ 19,560	$ 18,183	$ 24,047	$ 12,541
General and administrative	1,973	1,513	6,032	3,978	7,119	6,037
Total operating expenses	8,900	7,734	25,592	22,161	31,166	18,578
Loss from operations	(8,900)	(7,734)	(25,592)	(22,161)	(31,166)	(18,578)
Other income (expense):
Change in fair value of Series B tranche rights	(10,631)		(11,256)			363
Other expense	(2)	(3)	(22)	(7)	(47)	(59)
Interest income	2	164	138	331	509	228
Total other income (expense), net	(10,631)	161	(11,140)	324	462	532
Net loss and comprehensive loss	(19,531)	(7,573)	(36,732)	(21,837)	(30,704)	(18,046)
Accretion of discount and dividends on redeemable convertible preferred stock	(2,848)	(1,578)	(8,298)	(1,609)	(4,287)	(98)
Net loss attributable to common stockholders	$ (22,379)	$ (9,151)	$ (45,030)	$ (23,446)	$ (34,991)	$ (18,144)
Net loss per share attributable to common stockholders—basic and diluted	$ (21.73)	$ (9.67)	$ (44.58)	$ (25.48)	$ (37.42)	$ (22.88)
Weighted-average number of common shares outstanding—basic and diluted	1,030,000	946,000	1,010,000	920,000	935,000	793,000
Pro forma net loss per share, basic and diluted	$ (21.73)	$ (9.67)	$ (44.58)	$ (25.48)	$ (37.42)	$ (22.88)
Pro forma weighted average common shares outstanding	1,030,000	946,000	1,010,000	920,000	935,000	793,000
Pro Forma [Member]
Other income (expense):
Net loss attributable to common stockholders					$ (30,704)
Net loss per share attributable to common stockholders—basic and diluted					$ (3.35)
Weighted-average number of common shares outstanding—basic and diluted					9,160,000
Pro forma net loss per share, basic and diluted					$ (3.35)
Pro forma weighted average common shares outstanding					9,160,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Series A One Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]
Balance at Dec. 31, 2017					$ 36,315
Balance (in shares) at Dec. 31, 2017					46,068,750
Balance at Dec. 31, 2017	$ (22,281)		$ 656	$ (22,937)
Balance (in shares) at Dec. 31, 2017		720,671
Issuance of Series B preferred stock					$ 24,480
Issuance of Series B preferred stock (Shares)					30,599,992
Series A-1 preferred stock accretion	(98)		(98)		$ 98
Series A-1 and Series B preferred stock dividends and accretion	(98)
Stock-based compensation expense	326		326
Conversion of Series A-1 preferred stock					(168,750)
Conversion of Series A-1 preferred stock		13,959
Vesting of restricted common stock		137,188
Exercise of options to purchase common stock	22		22
Exercise of options to purchase common stock (Shares)		9,558
Net loss	(18,046)			(18,046)
Balance at Dec. 31, 2018					$ 60,893
Balance (in shares) at Dec. 31, 2018					76,499,992	0
Balance at Dec. 31, 2018	(40,077)		906	(40,983)
Balance (in shares) at Dec. 31, 2018		881,376
Series A-1 preferred stock accretion	(31)		(31)		$ 31
Stock-based compensation expense	210		210
Vesting of restricted common stock		38,862
Exercise of options to purchase common stock	28		28
Exercise of options to purchase common stock (Shares)		17,443
Net loss	(14,264)			(14,264)
Balance at Jun. 30, 2019					$ 60,924
Balance (in shares) at Jun. 30, 2019					76,499,992
Balance at Jun. 30, 2019	(54,134)		1,113	(55,247)
Balance (in shares) at Jun. 30, 2019		937,681
Balance at Dec. 31, 2018					$ 60,893
Balance (in shares) at Dec. 31, 2018					76,499,992	0
Balance at Dec. 31, 2018	(40,077)		906	(40,983)
Balance (in shares) at Dec. 31, 2018		881,376
Series A-1 and Series B preferred stock dividends and accretion	(1,609)
Net loss	(21,837)
Balance at Sep. 30, 2019					$ 61,900	$ 46,240
Balance (in shares) at Sep. 30, 2019					76,499,992	55,486,215
Balance at Sep. 30, 2019	(63,051)			(63,051)
Balance (in shares) at Sep. 30, 2019		970,640
Balance at Dec. 31, 2018					$ 60,893
Balance (in shares) at Dec. 31, 2018					76,499,992	0
Balance at Dec. 31, 2018	(40,077)		906	(40,983)
Balance (in shares) at Dec. 31, 2018		881,376
Issuance of Series B preferred stock						$ 51,452
Issuance of Series B preferred stock (Shares)						62,535,183
Series A-1 and Series B preferred stock dividends and accretion	(4,287)		(1,677)	(2,610)	$ 2,601	$ 1,686
Series A-1 and Series B preferred stock dividends and accretion	(4,287)
Stock-based compensation expense	711		711
Vesting of restricted common stock		71,312
Exercise of options to purchase common stock	$ 60		60
Exercise of options to purchase common stock (Shares)	36,012	36,012
Net loss	$ (30,704)			(30,704)
Balance at Dec. 31, 2019					$ 63,494	$ 53,138
Balance (in shares) at Dec. 31, 2019					76,499,992	62,535,000
Balance at Dec. 31, 2019	(74,297)			(74,297)
Balance (in shares) at Dec. 31, 2019		988,700
Balance at Jun. 30, 2019					$ 60,924
Balance (in shares) at Jun. 30, 2019					76,499,992
Balance at Jun. 30, 2019	(54,134)		1,113	(55,247)
Balance (in shares) at Jun. 30, 2019		937,681
Issuance of Series B preferred stock						$ 45,638
Issuance of Series B preferred stock (Shares)						55,486,215
Series A-1 and Series B preferred stock dividends and accretion					$ 976	$ 602
Series A-1 and Series B preferred stock dividends and accretion	(1,578)		(1,347)	(231)
Stock-based compensation expense	201		201
Vesting of restricted common stock		16,225
Exercise of options to purchase common stock	33		33
Exercise of options to purchase common stock (Shares)		16,734
Net loss	(7,573)			(7,573)
Balance at Sep. 30, 2019					$ 61,900	$ 46,240
Balance (in shares) at Sep. 30, 2019					76,499,992	55,486,215
Balance at Sep. 30, 2019	(63,051)			(63,051)
Balance (in shares) at Sep. 30, 2019		970,640
Balance at Dec. 31, 2019					$ 63,494	$ 53,138
Balance (in shares) at Dec. 31, 2019					76,499,992	62,535,000
Balance at Dec. 31, 2019	(74,297)			(74,297)
Balance (in shares) at Dec. 31, 2019		988,700
Series A-1 and Series B preferred stock dividends and accretion	5,450		624	(4,826)	$ 3,140	$ 2,310
Stock-based compensation expense	619		619		0
Vesting of restricted common stock		14,026
Exercise of options to purchase common stock	5		5
Exercise of options to purchase common stock (Shares)		1,562
Net loss	(17,201)			(17,201)
Balance at Jun. 30, 2020					$ 66,634	$ 55,448
Balance (in shares) at Jun. 30, 2020					76,499,992	62,535,183
Balance at Jun. 30, 2020	(96,324)			(96,324)
Balance (in shares) at Jun. 30, 2020		1,004,288
Balance at Dec. 31, 2019					$ 63,494	$ 53,138
Balance (in shares) at Dec. 31, 2019					76,499,992	62,535,000
Balance at Dec. 31, 2019	(74,297)			(74,297)
Balance (in shares) at Dec. 31, 2019		988,700
Series A-1 and Series B preferred stock dividends and accretion	$ (8,298)
Exercise of options to purchase common stock (Shares)	64,062
Net loss	$ (36,732)
Balance at Sep. 30, 2020					$ 68,220	$ 105,668
Balance (in shares) at Sep. 30, 2020					76,499,992	104,225,000
Balance at Sep. 30, 2020	(118,257)			(118,257)
Balance (in shares) at Sep. 30, 2020		1,071,959
Balance at Jun. 30, 2020					$ 66,634	$ 55,448
Balance (in shares) at Jun. 30, 2020					76,499,992	62,535,183
Balance at Jun. 30, 2020	(96,324)			(96,324)
Balance (in shares) at Jun. 30, 2020		1,004,288
Issuance of Series B preferred stock						$ 35,826
Issuance of Series B preferred stock (Shares)						41,690,117
Series A-1 and Series B preferred stock dividends and accretion					$ 1,586	$ 1,262
Series A-1 and Series B preferred stock dividends and accretion	(2,848)		(446)	(2,402)
Settlement of Series B tranche rights						13,132
Stock-based compensation expense	340		340
Vesting of restricted common stock		5,171
Exercise of options to purchase common stock	106		$ 106
Exercise of options to purchase common stock (Shares)		62,500
Net loss	(19,531)			(19,531)
Balance at Sep. 30, 2020					$ 68,220	$ 105,668
Balance (in shares) at Sep. 30, 2020					76,499,992	104,225,000
Balance at Sep. 30, 2020	$ (118,257)			$ (118,257)
Balance (in shares) at Sep. 30, 2020		1,071,959

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net loss	$ (36,732)	$ (21,837)	$ (30,704)	$ (18,046)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	983	786	1,071	956
Stock-based compensation	959	411	711	326
Loss on disposal of fixed assets			47
Change in fair value of Series B tranche rights	11,256			(363)
Changes in:
Prepaid expenses and other current assets	(962)	(253)	212	(280)
Accounts payable and other current liabilities	103	(91)	(33)	823
Accrued expenses and other current liabilities	(885)	2,506	1,915	(197)
Deferred rent	(349)	(317)	(423)	(382)
Net cash used in operating activities	(25,627)	(18,795)	(27,204)	(17,163)
Investing Activities
Purchase of property and equipment	(1,014)	(598)	(977)	(291)
Net cash used in investing activities	(1,014)	(598)	(977)	(291)
Financing activities
Proceeds from exercise of options to purchase common stock	111	61	60	22
Proceeds from Issuance of Convertible Preferred Stock				24,480
Proceeds from issuance of Series B preferred stock and tranche liability	35,826	47,303	53,328
Payment of deferred offering costs	(563)
Net cash provided by financing activities	35,374	47,364	53,388	24,502
Increase in cash and cash equivalents	8,733	27,971	25,207	7,048
Cash and cash equivalents at beginning of period	45,286	20,079	20,079	13,031
Cash and cash equivalents at end of period	54,019	48,050	45,286	20,079
Non-cash investing and financing activities
Purchase of property and equipment in accrued expenses		114	316
Accretion of discount and dividends on preferred stock	8,298	$ 1,609	$ 4,287	$ 98
Deferred offering costs in accounts payable and accrued expenses	944
Settlement of Series B tranche rights	$ 13,132

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Organization Oncorus, Inc. (the “Company”) is a biopharmaceutical company focused on developing next-generation viral immunotherapies to transform outcomes for cancer patients. Using its two platforms, the Company is developing a pipeline of intratumorally and intravenously administered product candidates designed to selectively attack and kill tumor cells. The Company’s operations to date have focused on organization and staffing, business planning, raising capital, acquiring and developing the Company’s technology, establishing the Company’s intellectual property portfolio, identifying potential product candidates and undertaking preclinical studies, clinical trials and manufacturing. The Company does not have any product candidates approved for sale and has not generated any revenue from product sales. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. On October 6, 2020, the Company completed an initial public offering (“IPO”), in which the Company issued and sold 5,800,000 shares of its common stock at a public offering price of $15.00 per share. On October 14, 2020, the Company sold an additional 757,991 shares of common stock at $15.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock. The total gross proceeds from the IPO were $98.4 million and the Company raised approximately $88.3 million in net proceeds after deducting underwriting discounts and commissions and offering expenses payable by the Company. Upon the closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 14,951,519 shares of common stock at the applicable conversion ratio then in effect. Subsequent to the closing of the IPO, there were no shares of preferred stock outstanding. In connection with the closing of the IPO, the Company filed its amended and restated certificate of incorporation pursuant to which it is authorized to issue up to 100,000,000 shares designated as common stock and 10,000,000 shares designated as preferred stock, all with a par value of $0.0001 per share. The condensed consolidated financial statements as of September 30, 2020, including share and per share amounts, do not give effect to the IPO, as it closed subsequent to September 30, 2020. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, possible failure of preclinical studies or clinical trials, the need to obtain marketing approval for its product candidates, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and the ability to secure additional capital to fund operations. Product candidates currently under development 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. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Basis of Presentation and Liquidity The accompanying unaudited interim condensed consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and as amended by Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements include all normal and recurring adjustments (which consist primarily of accruals and estimates that impact the financial statements) which are considered necessary to present fairly the Company’s financial position as of September 30, 2020, its results of operations for the three and nine months ended September 30, 2020 and 2019, its changes in redeemable convertible preferred stock and stockholders’ deficit for the three and nine months ended September 30, 2020 and 2019 and its cash flows for the nine months ended September 30, 2020 and 2019. The accompanying unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the accompanying notes for the year ended December 31, 2019 found elsewhere in this prospectus. On September 23, 2020 and September 25, 2020, the Company’s board of directors and stockholders, respectively, approved a one-for-12.0874 paid-in The Company’s unaudited interim condensed consolidated financial statements as of September 30, 2020 have been prepared on the basis of the Company continuing as a going concern for the next 12 months. Management believes that the Company’s existing cash and cash equivalents, together with the net proceeds from the IPO, will allow the Company to continue its operations for at least the next 12 months. In the absence of a significant source of recurring revenue, the continued viability of the Company is dependent on its ability to continue to raise additional capital to finance its operations. If the Company is unable to obtain additional funding, the Company may 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.	1. Nature of the Business and Liquidity Oncorus, Inc. (the “Company”) is a biopharmaceutical company focused on developing next-generation viral immunotherapies to transform outcomes for cancer patients. Using its two platforms, the Company is developing a pipeline of intratumorally and intravenously administered product candidates designed to selectively attack and kill tumor cells. The Company’s operations to date have focused on organization and staffing, business planning, raising capital, acquiring and developing the Company’s technology, establishing the Company’s intellectual property portfolio, identifying potential product candidates and undertaking preclinical studies and manufacturing. The Company does not have any product candidates approved for sale and has not generated any revenue from product sales. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, possible failure of preclinical studies or clinical trials, the need to obtain marketing approval for its product candidates, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and the ability to secure additional capital to fund operations. Product candidates currently under development 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. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The Company has funded its operations to date primarily through private sales of redeemable convertible preferred stock. Going Concern In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), The Company has incurred recurring negative cash flows since inception and has funded its operations primarily from the sale of redeemable convertible preferred stock. The Company had an accumulated deficit of $74.3 million as of December 31, 2019. The Company had net losses of $18.0 million and $30.7 million for the years ended December 31, 2018 and 2019, respectively. The Company expects to continue to incur significant expenses and operating losses for the foreseeable future. As of July 29, 2020, the issuance date of these consolidated financial statements for the year ended December 31, 2019, the Company expects its cash and cash equivalents of $45.3 million as of December 31, 2019 will not be sufficient to fund the operating expenses and capital expenditure requirements necessary to advance its research efforts and clinical trials for one year from the issuance date of these consolidated financial statements and the Company will need to obtain additional funding. Upon reaching certain clinical development milestones for the Company’s primary clinical candidate, as defined in the terms of the Series B Redeemable Convertible Preferred Stock (“Series B”) stock purchase agreement, the Company is eligible to receive funding through the additional sale of Series B (see Note 6) in the amount of $35.8 million. In addition, the Company intends to pursue a public offering of its common stock to fund future operations. There can be no assurances, however, that the current operating plan or clinical development milestone will be achieved or that additional funding will be available or on terms acceptable to the Company. If the Company is unable to obtain sufficient funding, it could be required to delay its development efforts, limit activities and reduce research and development costs, which could adversely affect its business prospects. Based on the Company’s recurring losses and negative cash flows from operations since inception, expectation of continuing operating losses and negative cash flows from operations for the foreseeable future, and the need to raise additional capital to finance its future operations, the Company’s management concluded that there is substantial doubt about the Company’s ability to continue as a going concern within one year after the issuance date of the consolidated financial statements for the year ended December 31, 2019. The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies COVID-19 With the ongoing COVID-19 COVID-19 re-organized COVID-19 COVID-19 Principles of Consolidation The accompanying unaudited interim condensed consolidated financial statements of the Company include the accounts of its wholly owned subsidiary, Oncorus Securities Corporation. All intercompany transactions have been eliminated in consolidation. The Company has one operating segment. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, the estimated fair value of the Company’s common stock and share-based awards utilized for stock-based compensation purposes, the Company’s Series B tranche rights (see Note 5), accrued expenses, and amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Classification and Measurement of Series A-1 Upon the closing of the IPO on October 6, 2020, all shares of preferred stock converted into common stock. Prior to the IPO, the Company classified its Series A-1 A-1”) A-1 A-1 A-1 480-10-S99. A-1 A-1 Deferred Offering Costs The Company capitalizes certain legal, professional, accounting and other third-party fees that are directly associated with in-process paid-in Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all of its cash at one financial institution, that management believes to be of high credit quality, in amounts that exceed federally insured limits. Cash equivalents consist of money market funds that invest primarily in U.S. government-backed securities and treasuries. The Company is dependent upon a third-party contract manufacturer and third-party contract research organizations for the performance of portions of its testing for pre-clinical Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1 Level 2 Level 3 To the extent a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s cash equivalents, classified within Level 1, are valued using net asset value per share for the money market funds. The tranche rights granted to the Series B stockholders (the “Series B Tranche Rights”) were classified within Level 3 of the fair value hierarchy because they were valued using significant inputs not observable in the market. The valuation of the tranche rights used assumptions the Company believed would be made by a market participant. The Company assessed these estimates on an ongoing basis as additional data impacting the assumptions was obtained. Refer to Note 5 for additional information regarding the valuation of the tranche rights. The Company believes that the carrying amounts of prepaid expenses, other current assets, accounts payable, and accrued expenses approximate their fair value due to the short-term nature of those instruments. Research Contract Costs and Accruals The Company has entered into various research service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzes the progress of the studies, trials or other services performed, including invoices received and contracted costs. Judgments and estimates are made in determining the accrued expense balances at the end of each reporting period. Net Loss Per Share Net loss per share attributable to common stockholders is calculated using the two-class A-1 as-converted Diluted net loss per share is computed using the more dilutive of (a) the two-class if-converted A-1, Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use 2016-02, 2016-02 2016-02 right-to-use In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework 2018-13”), 2018-13 2018-13	2. Summary of Significant Accounting Policies Basis of Presentation These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and ASU of the FASB. Principles of Consolidation The accompanying consolidated financial statements of the Company include the accounts of its wholly owned subsidiary, Oncorus Securities Corporation. All intercompany transactions have been eliminated in consolidation. The Company has one operating segment. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, the estimated fair value of the Company’s common stock and share-based awards utilized for stock-based compensation purposes, the Company’s Series A-1 Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all of its cash at one financial institution that management believes to be of high credit quality, in amounts that exceed federally insured limits. Cash equivalents consist of money market funds that invest primarily in U.S. government-backed securities and treasuries. The Company is dependent upon a third-party contract manufacturer and third-party contract research organizations for the performance of portions of its testing for pre-clinical Research and Development Expenses Research and development expenses are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including compensation-related expenses for research and development personnel, including stock-based compensation expense, preclinical and clinical activities, costs of manufacturing, overhead expenses including facilities and laboratory expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation and amortization. Upfront and annual license payments related to acquired technologies or technology licenses which have not yet reached technological feasibility and have no alternative future use are also included in research and development expense for the period in which they are incurred. General and Administrative Expenses General and administrative expenses consist primarily of salaries and related costs, including stock-based compensation expense, for personnel in executive, finance and accounting, business development, operations and administrative functions. General and administrative expenses also include fees for legal, consulting, accounting and audit services as well as insurance, outside service providers, direct and allocated facility-related costs and depreciation and amortization. Interest Income on Investments Interest income is separately presented on the consolidated statements of operations and comprehensive loss and consists of interest on cash and cash equivalents. Cash and Cash Equivalents The primary objectives for the Company’s investment portfolio are the preservation of capital and maintenance of liquidity. The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. At December 31, 2018 and 2019, cash and cash equivalents include bank demand deposits and money market funds that invest primarily in U.S. government-backed securities and treasuries. Cash equivalents are stated at cost, which is substantially equivalent to fair value. Property and Equipment, Net Property and equipment are recorded at cost. Expenditures for major renewals or betterments that extend the useful lives of property and equipment are capitalized; expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related assets. Property and equipment are depreciated as follows: ASSET TYPE ESTIMATED USEFUL LIFE Computer equipment and software 3-5 years Furniture and fixtures 5 years Laboratory equipment 5 years Leasehold improvements Shorter of lease term or estimated useful life Upon retirement or sale, the cost and related accumulated depreciation and amortization of assets disposed of are removed from the accounts, and any resulting gain or loss is included in loss from operations as a component of other income (expense). Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review were to be performed to evaluate a long-lived asset for recoverability, the Company would compare forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized if estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1 Level 2 Level 3 To the extent a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s cash equivalents, classified within Level 1, are valued using net asset value per share for the money market funds. The Company’s Series A-1 on-going A-1 The Company believes that the carrying amounts of prepaid expenses, other current assets, accounts payable, and accrued expenses approximate their fair value due to the short-term nature of those instruments. Research Contract Costs and Accruals The Company has entered into various research service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzes the progress of the studies, trials or other services performed, including invoices received and contracted costs. Judgments and estimates are made in determining the accrued expense balances at the end of each reporting period. Deferred Rent The Company has received tenant improvement consideration from its landlord as well as free rental periods, each of which are amortized on a straight-line basis over the term of the lease. Patent Costs The Company expenses patent costs as incurred and records such costs within general and administrative expenses. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ (deficit) equity that result from transactions and economic events other than those with stockholders. For all periods presented, net loss is the same as comprehensive loss as there are no comprehensive income items. Classification and Measurement of Series A-1 The Company has classified its Series A-1 A-1”) A-1 A-1 A-1 480-10-S99. A-1 Series A-1 Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the consolidated financial statement and tax bases of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be realized and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The potential for recovery of deferred tax assets is evaluated by analyzing carryback capacity in periods with taxable income, reversal of existing taxable temporary differences and estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step more-likely-than-not Stock-Based Compensation The Company measures all stock options and other stock-based awards granted based on the fair value of the award on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has elected to recognize forfeitures as they occur. The reversal of compensation cost previously recognized for an award that is forfeited because of a failure to satisfy a service or performance condition is recognized in the period of the forfeiture. Generally, the Company issues stock options and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method over the requisite service period. In November 2018, the Company granted a performance-based option to an employee with a total fair value of $0.1 million. A portion of these options vested upon the closing of the Series B financing and stock compensation of $0.04 million was recorded in 2019 related to these vested options. The vesting condition for the remainder of these options was not considered probable and as a result, no stock-based compensation was recorded related to this portion of the award during the year ended December 31, 2019. Prior to the adoption of ASU No. 2018-07, Compensation—Stock Compensation non-employee non-employees No. 2018-07. The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company estimates the fair value of common stock using an appropriate valuation methodology, in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation The fair value of each stock option grant is estimated using the Black-Scholes option-pricing model. The Company is a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies within the biotechnology industry with characteristics similar to the Company. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is Net Loss Per Share Net loss per share attributable to common stockholders is calculated using the two-class A-1 as-converted Diluted net loss per share is computed using the more dilutive of (a) the two-class if-converted A-1, Deferred Offering Costs The Company capitalizes certain legal, professional, accounting and other third-party fees that are directly associated with in-process equity issuances as deferred offering costs until such equity issuances are consummated. After consummation of the equity issuance, these costs are recorded as a reduction in the capitalized amount associated with the equity issuance. Should the equity issuance be delayed or abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss. During 2019, the Company incurred $1.5 million of deferred offering costs related to the Company’s proposed initial public offering (“IPO”). These offering costs were expensed at December 31, 2019 due to the expected timing of the Company’s proposed IPO. Pro Forma Financial Information (unaudited) Upon the closing of a qualified IPO (as defined in the Company’s Certificate of Incorporation), all of the Company’s outstanding shares of Series A-1 A-1 A-1 A-1 Series A-1 A-1 The following table summarizes the Company’s unaudited pro forma net loss per share attributable to common stockholders (in thousands, except per share data): YEAR ENDED Numerator: Net loss attributable to common stockholders $ (34,991 ) Accretion of discount and dividends on redeemable convertible preferred stock 4,287 Pro forma net loss attributable to common stockholders $ (30,704 ) Denominator: Weighted average number of common shares outstanding 935 Pro forma weighted average shares outstanding after giving effect to the conversion of 8,225 Pro forma weighted average common shares outstanding 9,160 Pro forma basic and diluted net loss per share attributable to common stockholders, basic and diluted $ (3.35 ) In November 2018, the Company granted a performance-based stock option to an employee for which a portion of the vesting is triggered by completion of an IPO. The stock-based compensation expense related to the vesting of this performance award is not included in the pro forma amounts above as the impact would be immaterial. Subsequent Events The Company considers events or transactions that occur after the balance sheet date but prior to the date the financial statements are issued for potential recognition or disclosure in the financial statements. The Company has completed an evaluation of all subsequent events after the audited balance sheet date of December 31, 2019 through the date the financial statements were issued, to ensure that these financial statements include appropriate disclosure of events both recognized in the financial statements as of December 31, 2019 and events which occurred subsequently but were not recognized in the financial statements. Refer to Note 14 for disclosure of material subsequent events. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 will a right-of-use asset 2016-02, ASU 2016-02 is 2016-02 right-to-use In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework 2018-13”), 2018-13 2018-13

Fair Value Measurements

Fair Value Measurements	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 51,555 $ — $ — $ 51,555 $ 51,555 $ — $ — $ 51,555 FAIR VALUE MEASUREMENTS LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 38,430 $ — $ — $ 38,430 $ 38,430 $ — $ — $ 38,430 Liabilities: Series B tranche rights $ — $ — $ 1,876 $ 1,876 $ — $ — $ 1,876 $ 1,876	3. Fair Value Measurements The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AS OF DECEMBER 31, 2018 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 19,881 $ — $ — $ 19,881 $ 19,881 $ — $ — $ 19,881 FAIR VALUE MEASUREMENTS AS OF DECEMBER 31, 2019 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 38,430 $ — $ — $ 38,430 $ 38,430 $ — $ — $ 38,430 Liabilities: Series B tranche rights $ — $ — $ 1,876 $ 1,876 $ — $ — $ 1,876 $ 1,876 Information regarding the valuation method and significant assumptions used in valuing the Series B tranche rights is included in Note 6.

Property Plant And Equipment

Property Plant And Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property Plant And Equipment [Text Block]	4. Property and Equipment Property and equipment, net as of December 31, 2018 and 2019 consisted of the following (in thousands): DECEMBER 31, 2018 2019 Laboratory equipment $ 2,514 $ 3,144 Computer equipment and software 41 114 Furniture and fixtures 159 313 Leasehold improvements 3,427 3,427 Fixed assets not yet placed in service — 328 6,141 7,326 Less accumulated depreciation (1,841 ) (2,851 ) Total property and equipment, net $ 4,300 $ 4,475 Depreciation expense was $1.0 million and $1.1 million for the years ended December 31, 2018 and 2019, respectively, which is included within operating expenses in the consolidated statement of operations and comprehensive loss.

Accrued Expenses

Accrued Expenses	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued Expenses	4. Accrued Expenses At September 30, 2020 and December 31, 2019, accrued expenses consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued research and development costs $ 890 $ 1,614 Accrued compensation 901 961 Accrued professional fees 1,176 564 Miscellaneous accrued expenses 188 382 Total accrued expenses $ 3,155 $ 3,521	5. Accrued Expenses At December 31, 2018 and 2019, accrued expenses consisted of the following (in thousands): AS OF DECEMBER 31, 2018 2019 Accrued research and development costs $ 466 $ 1,614 Accrued compensation 617 961 Accrued professional fees 114 564 Miscellaneous accrued expenses 93 382 Total accrued expenses $ 1,290 $ 3,521

Series A-1 and Series B Tranche

Series A-1 and Series B Tranche Rights	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Warrants and Rights Note Disclosure [Abstract]
Series A-1 and Series B Tranche Rights	5. Series B Tranche Rights Included in the terms of the purchase agreement for the Series B (“Series B Purchase Agreement”) were Series B Tranche Rights granted to the purchasers of the Series B. The Series B Tranche Rights provided the holders with the right to purchase additional shares of Series B, in a second tranche, upon either the achievement by the Company of certain clinical development milestones for the Company’s primary clinical candidate, as set forth in the Series B Purchase Agreement, or upon the election of certain holders of the Series B prior to August 5, 2021. In the second tranche, the Company had the ability to sell up to 41,690,117 shares of Series B at $0.8597 per share. The Company reached the clinical development milestones set forth in the Series B Purchase Agreement in September 2020 and the Company sold 41,690,177 shares of Series B at $0.8597 per share, resulting in total gross proceeds to the Company of $35.8 million. At the time of issuance, the Series B Tranche Rights met the definition of a freestanding financial instrument, as the Series B Tranche Rights were both legally detachable and separately exercisable from the Series B. In addition, the Company determined at the time of issuance that the Series B Tranche Rights met the definition of a liability (or in some circumstances, an asset) because the Series B Tranche Rights (i) embodied an obligation to repurchase the Company’s equity shares and (ii) may have required the Company to settle the obligation by transferring assets. As a result, upon issuance, the respective Series B Tranche Rights were initially recorded at fair value and were subsequently re-measured At December 31, 2019 and at the end of each reporting period prior to settlement in September 2020, the estimated fair value of the Series B Tranche Rights was determined using a probability weighted present value model that considered the probability of triggering the Series B Tranche Rights through achievement of the clinical development milestones specified in the Series B Purchase Agreement. The Company converted the future values to their present values using a discount rate it considered to be appropriate for probability adjusted cash flows. The estimates were based, in part, on subjective assumptions. Significant assumptions for the Series B Tranche Rights valuations at December 31, 2019 and in 2020, prior to settlement, included an 85% to 90% range of probability of achieving the clinical development milestones and discount rates ranging from 0.2% to 1.9%. The Company remeasured the fair value of the tranche rights for a final time at the date of settlement on September 17, 2020. As the clinical development milestones triggering the tranche closing were achieved, the fair value of the tranche rights at settlement was derived based on the implied intrinsic value of the Series B on the day of the second tranche closing event. The fair value of the Series B at settlement was $1.18 per share and was based on the probability of the conversion of the Series B upon an IPO and the expected value of the shares, on a converted basis, in an IPO. The increase in the probability of the achievement of the milestone, as well as the increase in the fair value of the Series B, resulted in an increase of $10.6 million in the fair value of the Series B Tranche Rights in the three months ended September 30, 2020 that was recognized as a loss in the accompanying unaudited interim condensed consolidated statement of operations and comprehensive loss at settlement. The balance of the Series B Tranche Rights of $13.1 million was reclassified at settlement to increase the Series B carrying value on the accompanying unaudited interim condensed consolidated balance sheet. A rollforward of the Series B Tranche Rights liability for the nine months ended September 30, 2020 is as follows (in thousands): SERIES B Balance at December 31, 2019 $ 1,876 Change in fair value 11,256 Reclassification of Series B Tranche Rights upon settlement (13,132 ) Balance at September 30, 2020 $ —	6. Series A-1 Series A-1 Tranche Rights Included in the terms of the purchase agreement for the Series A-1 A-1 A-1 The Series A-1 Tranche Rights provided the holders with the right to purchase additional shares of Series A-1 A-2 A-2”) Series A-1 A-2 Series A-1. re-measured While outstanding, the estimated fair value of the Series A-1 Tranche Rights was determined using a probability-weighted present value model that considered the probability of triggering the Series A-1 Tranche Rights through achievement of the clinical development milestones specified in the Series A-1 Upon the issuance of Series A-1 A-1 Series A-2 A-1 A-1 A-1 Series A-2 Series A-2 This modification to the terms of the Series A-1 Tranche Rights was treated, in effect, as a settlement of the Series A-1 Tranche Rights and subsequent issuance of Series A-1. Series B Tranche Rights Included in the terms of the purchase agreement for the Series B (“Series B Purchase Agreement”) were tranche rights granted to the purchasers of the Series B (“Series B Tranche Rights”). The Series B Tranche Rights provide the holders with the right to purchase additional shares of Series B, in a future tranche, upon either the achievement by the Company of certain clinical development milestones for the Company’s primary clinical candidate, as set forth in the Series B Purchase Agreement, or upon the election of certain holders of the Series B prior to August 5, 2021. In the future tranche, the Company may sell up to 41,690,117 shares of Series B at $0.8597 per share, the full amount of which would result in gross proceeds to the Company of $35.8 million. At the time of issuance, the Series B Tranche Rights met the definition of a freestanding financial instrument, as the Series B Tranche Rights are both legally detachable and separately exercisable from the Series B. In addition, the Company determined at the time of issuance that the Series B Tranche Rights met the definition of a liability (or in some circumstances, an asset) because the Series B Tranche Rights (i) embody an obligation to repurchase the Company’s equity shares and (ii) may require the Company to settle the obligation by transferring assets. As a result, upon issuance, the respective Series B Tranche Rights were initially recorded at fair value and are subsequently re-measured While outstanding, the estimated fair value of the Series B Tranche Rights is determined using a probability-weighted present value model that considers the probability of triggering the Series B Tranche Rights through achievement of the clinical development milestones specified in the Series B Purchase Agreement. The Company converts the future values to their present values using a discount rate it considers to be appropriate for probability-adjusted cash flows. The estimates are based, in part, on subjective assumptions. Changes to these assumptions could have a significant impact on the reported fair value of the Series B Tranche Rights. Significant assumptions for the Series B Tranche Rights valuations at execution and December 31, 2019 include an 85% probability of achieving the clinical development milestones at both dates and a discount rate of 1.9% and 1.6%, respectively. A rollforward of the Series A-1 and Series B Tranche Rights liability for the years ended December 31, 2018 and 2019 is as follows (in thousands): SERIES A-1 SERIES B Balance at December 31, 2017 $ 363 $ — Change in fair value (363 ) — Balance at December 31, 2018 — — Change in fair value — — Issuance of Series B tranche rights liability — 1,876 Balance at December 31, 2019 $ — $ 1,876

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	6. Redeemable Convertible Preferred Stock At September 30, 2020, the Company had 180,725,292 shares of preferred stock, par value $0.0001 per share, in authorized capital, which consisted of 76,499,992 authorized, issued and outstanding shares of Series A-1 Upon the closing of the IPO on October 6, 2020, all of the outstanding shares of Series A-1 Issuance of Series B Redeemable Convertible Preferred Stock In August 2019, the Company authorized and agreed to sell 92,477,021 shares of Series B in two tranches. The first tranche closed on dates between August 5, 2019 and August 27, 2019. On those dates, the Company sold a total of 55,486,215 shares of Series B at $0.8597 per share, for gross proceeds to the Company of $47.7 million. In November 2019, the Company authorized and agreed to sell 11,748,279 additional shares of its Series B to new investors on the same terms and conditions as the previous sale of Series B. The first tranche of this sale occurred on November 27, 2019, in which the Company sold 7,048,968 shares of Series B for gross proceeds of $6.1 million. The Company paid $0.4 million of issuance costs related to these sales. In September 2020, the Company achieved the second tranche milestones related to the clinical development of its lead product candidate, ONCR-177. The following is a description of the rights and privileges of the Series B and A-1 Liquidation In the event of any voluntary or involuntary liquidation, dissolution, or winding-up A-1 A-1 A-1, A-1. A-1 A-1 as-converted A-1 Unless otherwise elected by 68% of the Series B holders, including certain identified Series B holders, a merger or consolidation involving the Company in which the stockholders of the Company did not own a majority of the outstanding shares of the surviving company was considered to be a Deemed Liquidation Event. A sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company was also considered a Deemed Liquidation Event. Redemption Upon the demand of the holders of at least 68% of the then outstanding shares of Series B, including certain identified Series B holders, but not prior to August 5, 2026, the Company had the obligation to redeem from each holder of Series B and Series A-1 A-1 A-1 A-1 A-1 A-1 480-10-S99. A-1 Series A-1 Series A-1. Conversion Each share of Series B and Series A-1 non-assessable A-1 A-1 A-1, All outstanding shares of Series B and Series A-1 A-1 Pay to Play Requirement All Series B holders were subject to a pay-to-play non-participating All Series A-1 pay-to-play non-participating A-1 A-1 A-1 A-1 Voting Rights The holders of Series B were entitled to vote, together with the holders of Series A-1 A-1 A-1 A-1 A-1 Dividends Series B holders were entitled to receive dividends at an annual rate of $0.06877 per share, which accrued from day to day, whether or not such dividends were declared by the Board of Directors, and were cumulative. The dividends were payable only when and if declared by the Board of Directors. The Company could not declare, pay or set aside any dividends on any other shares of capital stock unless the Series B holders first received, or simultaneously received, a dividend in an amount at least equal to the amount of the aggregate accumulated dividends that were accrued but not previously paid, or an amount equal to a formula, which was tied to dividends paid on other classes of stock. Holders of the Series A-1 A-1 A-1 A-1 A-1. A-1 A-1 “as-if” A-1 No dividends were paid to the holders of Series B or Series A-1	7. Redeemable Convertible Preferred Stock At December 31, 2019, the Company had 180,725,292 shares of preferred stock, par value $0.0001 per share, in authorized capital. At December 31, 2019, the preferred stock consisted of 76,499,992 authorized, issued and outstanding shares of Series A-1 Issuances of Series A-1 A-1 2016 Issuances On March 31, 2016, the Company issued 4,612,500 shares of Series A Redeemable Convertible Preferred Stock (“Series A”) at a price of $1.00 per share and warrants (the “Common Stock Warrants”) to purchase 57,239 shares of common stock at an exercise price of $1.21 per share for aggregate gross proceeds of $4.6 million. Each Common Stock Warrant initially entitled the holder to purchase one share of common stock. The Company incurred issuance costs of $0.4 million directly associated with the issuance of the Series A. On July 11, 2016, the Company and the holders of the Series A agreed to convert and exchange each share of Series A and each Common Stock Warrant into 1.25 shares of Series A-1 In addition, on July 11, 2016, the Company issued 16,137,499 shares of Series A-1 A-1 A-1 A-1. A-2 On October 27, 2016, the Company issued an additional 1,500,000 shares of Series A-1 A-1 A-1 A-1 A-2 2017 Issuances In June 2017, the first tranche was settled, and the Company issued 22,665,626 shares of Series A-1 2018 Issuances As previously disclosed in Note 6, the clinical development milestones set forth in the Series A-1 A-2 A-1 A-1 A-1 A-2 A-2 Issuance of Series B Redeemable Convertible Preferred Stock In August 2019, the Company authorized and agreed to sell 92,477,021 shares of Series B in two tranches. The first tranche closed on dates between August 5, 2019 and August 27, 2019. On those dates, the Company sold a total of 55,486,215 shares of Series B at $0.8597 per share, for gross proceeds to the Company of $47.7 million. In November 2019, the Company authorized and agreed to sell 11,748,279 additional shares of its Series B to new investors on the same terms and conditions as the previous sale of Series B. The first tranche of this sale occurred on November 27, 2019, in which the Company sold 7,048,968 shares of Series B for gross proceeds of $6.1 million. The Company paid $0.4 million of issuance costs related to these sales. The second tranche of the Series B will occur upon either achievement by the Company of certain clinical development milestones, as set forth in the Series B Purchase Agreement, for the Company’s primary clinical candidate, or upon election of certain holders of Series B prior to August 5, 2021. For the second tranche, the Company may sell up to 41,690,117 shares of Series B at $0.8597 per share, the full amount of which would result in gross proceeds to the Company of $35.8 million. The following is a description of the rights and privileges of the Series B and A-1: Liquidation In the event of any voluntary or involuntary liquidation, dissolution, or winding-up A-1 A-1 A-1, Series A-1. Series A-1 as-converted and A-1 Unless otherwise elected by 68% of the Series B holders, including certain identified Series B holders, a merger or consolidation involving the Company in which the stockholders of the Company do not own a majority of the outstanding shares of the surviving company is considered to be a Deemed Liquidation Event. A sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company is also considered a Deemed Liquidation Event. Redemption Upon the demand of the holders of at least 68% of the then outstanding shares of Series B, including certain identified Series B holders, but not prior to August 5, 2026, the Company shall redeem from each holder of Series B and Series A-1 A-1 and A-1 Series A-1 A-1 A-1 480-10-S99. A-1 Series A-1 A-1. Conversion Each share of Series B and Series A-1 non-assessable A-1 A-1 A-1, All outstanding shares of Series B and Series A-1 Pay to Play Requirement All Series B holders are subject to a pay-to-play non-participating All Series A-1 pay-to-play non-participating A-1 A-1 As of September 6, 2018, three investors chose not to participate in the Company’s second tranche of its Series A-1 Series A-1 Voting Rights The holders of Series B are entitled to vote, together with the holders of Series A-1 and common stock, on all matters submitted to stockholders for a vote. Each share of Series B and Series A-1 A-1 Series A-1 Series A-1 Dividends Series B holders are entitled to receive dividends at an annual rate of $0.06877 per share, which shall accrue from day to day, whether or not such dividends are declared by the Board of Directors, and shall be cumulative. The dividends shall be payable only when and if declared by the Board of Directors. The Company may not declare, pay or set aside any dividends on any other shares of capital stock unless the Series B holders first receive, or simultaneously receive, a dividend in an amount at least equal to the amount of the aggregate accumulated dividends that are accrued but not previously paid, or an amount equal to a formula, which is tied to dividends paid on other classes of stock. Holders of the Series A-1 A-1 A-1 “as-if” A-1

Common Stock

Common Stock	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Statement of Stockholders' Equity [Abstract]
Common Stock	7. Common Stock Each share of common stock is entitled to one vote. The holders of shares of common stock are entitled to receive dividends, if and when declared by the Board of Directors. Prior to the IPO, the voting, dividend, and liquidation rights of the holders of common stock were subject to, and qualified by, the rights, powers, and preferences of the holders of Series B and Series A-1 Upon the closing of the IPO, Company changed its authorized capital stock to include 100,000,000 shares designated as common stock with a par value of $0.0001 per share. Restricted Stock The Company issued restricted stock to its founders and certain officers of the Company. In general, the shares of restricted stock vest over a four-year period, with 25% of the shares vesting after one year, followed by monthly vesting over the remaining three years. A summary of non-vested AMOUNT WEIGHTED-AVERAGE Balance at December 31, 2019 41,602 $ 1.57 Repurchases — — Issuances — — Vested (19,197 ) 1.57 Balance at September 30, 2020 22,405 $ 1.57 Common Stock Warrants The Company issued warrants to purchase common stock (the “Common Stock Warrants”) in connection with its Series A financing in March 2016. The Common Stock Warrants allow for the holders to purchase 71,544 shares of common stock at $1.21 per share. As of September 30, 2020, all of the Common Stock Warrants were fully exercisable. The Common Stock Warrants expire in 2031. Reserved Shares The Company had reserved shares of common stock for the conversion or exercise of the following securities: SEPTEMBER 30, Conversion of Series A-1 6,328,894 Conversion of Series B 8,622,625 Exercise of Common Stock Warrants 71,544 Exercise of options to purchase common stock 2,109,151 Vesting of restricted stock 22,405 Shares available for issuance under the 2016 Plan 19,048 Total 17,173,667	8. Common Stock Each share of common stock is entitled to one vote. The holders of shares of common stock are entitled to receive dividends, if and when declared by the Board of Directors. The voting, dividend, and liquidation rights of the holders of common stock are subject to, and qualified by, the rights, powers, and preferences of the holders of Series B and Series A-1 Restricted Stock The Company issued restricted stock to its founders and certain officers of the Company. In general, the shares of restricted stock vest over a four-year period, with 25% of the shares vesting after one year, followed by monthly vesting over the remaining three years. A summary of non-vested AMOUNT WEIGHTED-AVERAGE Balance at December 31, 2018 154,590 $ 1.57 Repurchases (41,676 ) 1.57 Issuances — — Vested (71,312 ) 1.57 Balance at December 31, 2019 41,602 $ 1.57 Common Stock Warrants The Company issued the Common Stock Warrants in connection with its Series A financing in March 2016 (as described in Note 7). The Common Stock Warrants allow for the holders to purchase 71,544 shares of common stock at $1.21 per share. As of December 31, 2019, all of the Common Stock Warrants were fully exercisable. The Common Stock Warrants expire in 2031. The Company has reserved shares of common stock for the conversion or exercise of the following securities: DECEMBER 31, Conversion of Series A-1 6,328,894 Conversion of Series B 5,173,569 Exercise of common stock warrants 71,544 Exercise of options to purchase common stock 1,991,066 Vesting of restricted stock 41,602 Shares available for issuance under the Plan 201,224 Total 13,807,899

Equity Incentive Plan

Equity Incentive Plan	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Equity Incentive Plan	8. Equity Incentive Plan The Company adopted the 2016 Equity Incentive Plan, as amended, (the “2016 Plan”) on March 31, 2016. The 2016 Plan provided for the granting of stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock awards to employees, directors and non-employees. On September 23, 2020, the Company adopted the 2020 Equity Incentive Plan (“the 2020 Plan”), which became effective upon the execution of the underwriting agreement related to the IPO and will serve as the successor to the 2016 Plan. The 2020 Plan authorizes the award of stock options, restricted stock awards (“RSAs”), stock appreciation rights (“SARs”), restricted stock units (“RSUs”), cash awards, performance awards and stock bonus awards. Under the 2020 Plan, 2,800,000 shares of common stock, plus any reserved shares not issued or subject to outstanding grants under the 2016 Plan on the effective date of the 2020 Plan are reserved for issuance pursuant to awards granted under the 2020 Plan. The number of shares reserved for issuance under the 2020 Plan will increase automatically on January 1 of each fiscal year, starting on January 1, 2021 and ending on and including January 1, 2030, by the number of shares equal to 5% of the aggregate number of outstanding shares of common stock as of the immediately preceding December 31, or a lesser number of shares as may be determined by the board of directors (or an authorized committee thereof). Total stock-based compensation (including both stock option awards and restricted stock awards) was as follows: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 (in thousands) General and administrative $ 172 $ 112 $ 512 $ 255 Research and development 168 89 447 156 Total stock-based compensation $ 340 $ 201 $ 959 $ 411 Total stock-based compensation by award type was as follows: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 (in thousands) Restricted stock $ 8 $ 27 $ 24 $ 89 Stock options 332 174 935 322 Total stock-based compensation $ 340 $ 201 $ 959 $ 411 In November 2018, the Company granted an employee an option to purchase 85,943 shares of the Company’s common stock having an exercise price per share equal to the fair value of the Company’s common stock on the date of the grant. This grant is included in the outstanding options in the summary table below. Vesting of the option is based on certain performance criteria and shall vest as follows: (i) 16.66% of the shares vested upon the first closing of the Company’s Series B stock financing, (ii) 33.33% of the shares vest in 24 equal monthly installments beginning with the first month following the initial closing of the Series B stock financing, (iii) 25% of the shares vested upon the IPO and (iv) 25% of the shares vest in 24 equal monthly installments beginning with the first month following the IPO. Upon the closing of the Series B financing in August 2019, the option vested immediately with respect to 14,323 shares, and an additional 28,647 option shares began vesting over the following 24 months. Upon the closing of the IPO in October 2020, the option vested immediately with respect to 21,485 shares and the remainder began vesting at that time. In September 2020, the Company granted, contingent upon the Company entering into an underwriting agreement related to the IPO, certain employee options to purchase a total of 363,150 shares of the Company’s common stock having an exercise price equal to the IPO price. These options were granted on October 1, 2020, are not included in the table below and no stock compensation was recorded for these grants as of September 30, 2020. A summary of option activity is presented below: SHARES WEIGHTED WEIGHTED- AGGREGATE Outstanding at December 31, 2019 1,991,066 $ 3.41 Granted 182,147 7.47 Exercised (64,062 ) 1.70 Canceled, expired or forfeited — — Outstanding at September 30, 2020 2,109,151 $ 3.81 8.4 $ 23,604 Vested at September 30, 2020 791,272 $ 2.70 7.8 $ 9,736 The weighted average grant date fair value per share of options granted to employees, directors and non-employee The total fair value of restricted shares vested during the nine months ended September 30, 2020 and 2019 was $0.02 million and $0.09 million, respectively. At September 30, 2020, there were 19,048 shares of common stock available for grant under the 2016 Plan. On September 23, 2020, the Company adopted the 2020 Employee Stock Purchase Plan, or the ESPP, which became effective upon the execution of the underwriting agreement related to the IPO. The Company has initially reserved 280,000 shares of common stock for sale under the ESPP. The aggregate number of shares reserved for sale under the ESPP will increase automatically on January 1st of each fiscal year starting on January 1, 2021 and ending on and including January 1, 2030, by the number of shares equal to the lesser of (a) 1% of the total number of shares of common stock outstanding on the last day of the fiscal year prior to the date of such automatic increase and (b) 560,000 shares, provided that prior to the date of any such increase, the board of directors may determine a less number of shares for such increase.	9. Equity Incentive Plan The Company adopted the 2016 Equity Incentive Plan (the “Plan”) on March 31, 2016. The Plan, as amended, provides for the granting of stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock awards to employees, directors and non-employees. The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the range of assumptions for the years ended December 31, 2018 and 2019 as noted in the following table: YEARS ENDED DECEMBER 31, 2018 2019 Expected volatility 71.4%-77.7% 77.0%-78.7% Expected dividends 0.0% 0.0% Expected term (in years) 6.1-10 6.1-10 Risk-free rate 2.8%-3.2% 1.4%-2.4% Total stock-based compensation (including both stock option awards and restricted stock) was as follows: YEARS ENDED DECEMBER 31, 2018 2019 (in thousands) General and administrative $ 207 $ 361 Research and development 119 350 Total stock-based compensation $ 326 $ 711 Total stock-based compensation by award type was as follows: YEARS ENDED DECEMBER 31, 2018 2019 (in thousands) Restricted stock $ 199 $ 116 Stock options 127 595 Total stock-based compensation $ 326 $ 711 In November 2018, the Company granted an employee an option to purchase 85,943 shares of the Company’s common stock having an exercise price per share equal to the fair value of the Company’s common stock on the date of the grant. This grant is included in the outstanding options in the summary table below. Vesting of the option is based on certain performance criteria and shall vest as follows: (i) 16.66% of the shares vested upon the first closing of the Company’s Series B stock financing, (ii) 33.33% of the shares vest in 24 equal monthly installments beginning with the first month following the initial closing of the Series B stock financing, (iii) 25% of the shares vest on the date immediately prior to an IPO of the Company’s equity securities and (iv) 25% of the shares vest in 24 equal monthly installments beginning with the first month following the IPO. Upon the closing of the Series B financing in August 2019, the option vested immediately with respect to 14,318 shares, and an additional 28,645 option shares began vesting over the following 24 months. As of December 31, 2019, the vesting conditions of the options subject to an IPO were not considered probable, and no stock-based compensation was recorded related to this portion of the award. A summary of option activity under the Plan is presented below: SHARES WEIGHTED- AVERAGE WEIGHTED- AVERAGE AGGREGATE Outstanding at December 31, 2018 970,027 $ 1.74 Granted 1,109,073 4.74 Exercised (36,012 ) 1.62 Canceled, expired or forfeited (52,022 ) 2.14 Outstanding at December 31, 2019 1,991,066 $ 3.41 9.0 $ 6,696 Vested at December 31, 2019 455,449 $ 1.72 7.9 $ 2,301 The weighted average grant date fair value of options granted to employees, directors and non-employee consultants The total fair value of restricted shares vested during the years ended December 31, 2018 and 2019 was $0.2 million and $0.1 million, respectively. At December 31, 2019, there were 201,224 shares of common stock available for grant under the Plan.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes A reconciliation of income tax expense (benefit) at the statutory federal income tax rate and income taxes as reflected in the consolidated financial statements is as follows: DECEMBER 31, 2018 2019 Federal income tax benefit at statutory rate 21.0 % 21.0 % State income tax, net of federal benefit 6.3 6.1 Permanent differences 0.2 (0.3 ) Research and development credit benefit 3.4 5.1 Change in valuation allowance (30.9 ) (31.9 ) Effective income tax rate — % — % The Company had a net loss for 2018 and 2019 and no income tax benefit has been recorded due to the full valuation allowance. The components of the Company’s deferred taxes at December 31, 2018 and 2019 are as follows (in thousands): DECEMBER 31, 2018 2019 Deferred tax assets: Net operating loss carryforwards (federal and state) $ 9,864 $ 18,070 Tax credits (federal and state) 1,630 3,129 Accrued expenses and other liabilities 164 156 Capitalized research and development expenditures 835 835 Accrued landlord incentive 537 430 Stock based compensation — 88 13,030 22,708 Valuation allowance (12,417 ) (22,201 ) Deferred tax liabilities: Fixed assets (613 ) (507 ) (613 ) (507 ) Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets for each period presented. The valuation allowance was $12.4 million as of December 31, 2018 and $22.2 million as of December 31, 2019. The increase in the valuation allowance of approximately $9.8 million in 2019 was primarily a result of operating losses generated with no corresponding financial statement benefit. As of December 31, 2019, the Company had net operating loss carryforwards (“NOLs”) for federal income tax purposes of $66.4 million, of which $18.1 million will begin to expire in 2035, and approximately $48.3 million can be carried forward indefinitely. The Company also has $65.3 million of state net operating losses which expire at various dates through 2039. As of December 31, 2019, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $2.3 million and $1.1 million, respectively, which begin to expire in 2035 and 2030, respectively. Utilization of the NOL carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the NOL carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the NOL carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed, and any limitation is known, no adjustments have been reflected in the deferred tax asset for NOLs. For the year ended December 31, 2019, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. The Company had no unrecognized tax benefits or related interest and penalties for the years ended December 31, 2018 and 2019. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s tax years are still open under statute from the year of formation to the present. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. The Company set up a Massachusetts securities corporation in 2019. The securities corporation is taxed on its investment income at the rate of 1.32%. The securities corporation was not material to the 2019 tax provision.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Leases In May 2016, the Company entered into an operating lease agreement for its corporate headquarters in Cambridge, Massachusetts, with a seven-year term that expires in January 2024. Rental payments related to the lease commenced in January 2017. In connection with this lease, the Company was entitled to cash incentives from the landlord to be used for the construction of leasehold improvements within the facility. The Company received $2.7 million of such incentives, which were recorded as deferred rent on the balance sheet and are being amortized to rent expense over the lease term. The Company recognizes rent expense on a straight-line basis over the lease period and has recorded deferred rent for rent expense incurred but not yet paid. The Company recorded rent expense related to office and lab space under the lease of $0.4 million for each of the three months ended September 30, 2020 and 2019 and $1.1 million of rent expense for each of the nine months ended September 30, 2020 and 2019. The amount of variable rent expense for these periods was immaterial. Future minimum lease payments for the Company’s operating leases as of September 30, 2020 were as follows (in thousands): YEARS ENDING DECEMBER 31, 2020 (three months remaining) $ 370 2021 1,523 2022 1,569 2023 1,616 2024 48 $ 5,126 License and Royalty Agreements The Company has entered into license and royalty agreements for intellectual property with certain parties. Such arrangements require ongoing payments, including payments upon the achievement of certain development, regulatory and commercial milestones, receipt of sublicense income, as well as royalties on commercial sales. Payments under these arrangements are expensed as incurred. In connection with the first patient dosing in the Company’s clinical trial in June 2020, the Company became obligated to make certain milestone payments totaling $0.8 million. The Company’s material license and collaboration agreements are summarized below. Ospedale San Raffaele S.r.l. and Fondazione Telethon In December 2015, the Company entered into a license agreement with Ospedale San Raffaele S.r.l. and Fondazione Telethon, as amended, for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee, up to $3.9 million in milestone payments for the first indication, up to $5.7 million in milestone payments for each subsequent indication and a low single digit tiered royalty on net sales of any covered products. The agreement terminates upon the expiration of the last remaining royalty obligation for a licensed product. University of Pittsburgh In March 2016, the Company entered into a license agreement, as amended, with University of Pittsburgh for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee and up to $2.6 million in milestone payments through first commercial product sale and a low single digit royalty on net product revenue, subject to annual minimum amounts, through the expiration of the patent claims. Northwestern University In December 2018, the Company entered into a license agreement with Northwestern University for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee and up to $4.1 million in milestone payments through the first commercial product sale and an annual low single digit royalty on net sales, subject to annual minimum amounts, through the later of ten years from the first commercial sale or the expiration of the patent claims. WuXi Biologics Ireland Limited In July 2019, the Company entered into a license agreement with this entity for the use of certain patents and technology. Under the terms of the license, the Company agreed to an initial license payment of $0.3 million and is required to pay milestone payments for the first product developed, as well as additional products, in addition to royalties on net product revenue. For the first product developed, the Company is required to pay up to $8.0 million in certain clinical milestone payments. For the first three products developed, the Company is also required to pay up to $27.0 million in commercial milestone payments for each product that achieves specified net sales levels along with product approvals in several countries. The Company also agreed to pay tiered royalties on net sales of licensed products ranging in the low-single product-by-licensed country-by-country Related Party License and Royalty Agreements In connection with the prior sale of Series A redeemable convertible preferred stock, which was later converted to Series A-1, Also in connection with the sale of Series A redeemable convertible preferred stock, the Company entered into a patent assignment agreement with an investor under which that investor would receive $1.0 million upon regulatory approval of a product in the United States and an annual low single-digit royalty on net product revenue. The Company is not currently developing any product candidates using the patent that was assigned to the Company. In September 2016, the Company entered into a sublicense agreement with an entity affiliated with a stockholder of the Company for the use of certain patents and technology. Under the terms of the license, the Company is required to pay up to $7.6 million in milestone payments through first commercial product sale and an annual mid-single Litigation The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.	11. Commitments and Contingencies Leases In May 2016, the Company entered into an operating lease agreement for its corporate headquarters in Cambridge, Massachusetts, with a seven-year term that expires in January 2024. Rental payments related to the lease commenced in January 2017. In connection with this lease, the Company was entitled to cash incentives from the landlord to be used for the construction of leasehold improvements within the facility. The Company received $2.7 million of such incentives, which were recorded as deferred rent on the balance sheet and are being amortized to rent expense over the lease term. The Company recognizes rent expense on a straight-line basis over the lease period and has recorded deferred rent for rent expense incurred but not yet paid. During the years ended December 31, 2018 and 2019 the Company recognized total rent expense of $1.0 million and $1.0 million, respectively, related to office and lab space under the lease. The amount of variable rent expense for these periods was immaterial. Future minimum lease payments for the Company’s operating leases as of December 31, 2019 were as follows (in thousands): YEARS ENDING DECEMBER 31, 2020 $ 1,479 2021 1,523 2022 1,569 2023 1,616 2024 48 $ 6,235 License and Royalty Agreements The Company has entered into license and royalty agreements for intellectual property with certain parties. Such arrangements require ongoing payments, including payments upon the achievement of certain development, regulatory and commercial milestones, receipt of sublicense income, as well as royalties on commercial sales. Payments under these arrangements are expensed as incurred. The Company has not paid any royalties or milestone payments under these agreements through December 31, 2019. The Company’s material license and collaboration agreements are summarized below. Ospedale San Raffaele S.r.l. and Fondazione Telethon In December 2015, the Company entered into a license agreement with Ospedale San Raffaele S.r.l. and Fondazione Telethon, as amended, for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee, up to $3.9 million in milestone payments for the first indication, up to $5.7 million in milestone payments for each subsequent indication and a low single digit tiered royalty on net sales of any covered products. The agreement terminates upon the expiration of the last remaining royalty obligation for a licensed product. University of Pittsburgh In March 2016, the Company entered into a license agreement, as amended, with University of Pittsburgh for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee and up to $2.6 million in milestone payments through first commercial product sale and a low single digit royalty on net product revenue, subject to annual minimum amounts, through the expiration of the patent claims. Northwestern University In December 2018, the Company entered into a license agreement with Northwestern University for the use of certain patents and technology. The Company made an initial payment of $0.1 million, which amount was recorded as research and development expense. Under the terms of the license, the Company is required to pay an annual maintenance fee and up to $4.1 million in milestone payments through the first commercial product sale and an annual low single digit royalty on net sales, subject to annual minimum amounts, through the later of ten years from the first commercial sale or the expiration of the patent claims. WuXi Biologics Ireland Limited In July 2019, the Company entered into a license agreement with an entity for the use of certain patents and technology. Under the terms of the license, the Company agreed to an initial license payment of $0.3 million and is required to pay milestone payments for the first product developed, as well as additional products, in addition to royalties on net product revenue. For the first product developed, the Company is required to pay up to $8.0 million in certain clinical milestone payments. For the first three products developed, the Company is also required to pay up to $27.0 million in commercial milestone payments for each product that achieves specified net sales levels along with product approvals in several countries. The Company also agreed to pay tiered royalties on net sales of licensed products ranging in the low-single product-by-licensed country-by-country Related Party License and Royalty Agreements In connection with the sale of Series A preferred stock (see Note 7), certain investors are entitled to receive, in the aggregate, a royalty from the Company equal to 1% of net sales of Company products discovered or developed prior to an IPO by the Company. The royalty obligation expires upon the later of twelve years from the first commercial sale or the expiration of the patent. Also in connection with the sale of Series A, the Company entered into a patent assignment agreement with an investor under which that investor would receive $1.0 million upon regulatory approval of a product in the United States and an annual low single-digit royalty on net product revenue. The Company is not currently developing any product candidates using the patent that was assigned to the Company. In September 2016, the Company entered into a sublicense agreement with an entity affiliated with a stockholder of the Company for the use of certain patents and technology. Under the terms of the license, the Company is required to pay up to $7.6 million in milestone payments through first commercial product sale and an annual mid-single digit royalty on net sales through the expiration of the patent claims. The Company is not currently using the technology underlying these patents. Litigation The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Net Loss Per Share

Net Loss Per Share	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	10. Net Loss Per Share The following securities that could potentially dilute basic net loss per share in the future were not included in the computation of diluted net loss per share for the periods presented, because to do so would have been antidilutive: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Series A-1 6,328,894 6,328,894 6,328,894 6,328,894 Series B 8,622,625 4,590,404 8,622,625 4,590,404 Outstanding stock options 2,109,151 1,936,493 2,109,151 1,936,493 Restricted stock 22,405 57,828 22,405 57,828 Common stock warrants 71,544 71,544 71,544 71,544 Total 17,154,619 12,985,163 17,154,619 12,985,163	12. Net Loss Per Share The following securities that could potentially dilute basic net loss per share in the future were not included in the computation of diluted net loss per share for the periods presented, because to do so would have been antidilutive:​​​​​​​ YEARS ENDED 2018 2019 Series A-1 6,328,894 6,328,894 Series B — 5,173,569 Outstanding stock options 970,027 1,991,066 Restricted stock 154,590 41,602 Common stock warrants 71,544 71,544 Total 7,525,055 13,606,675

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Retirement Plan	13. Retirement Plan The Company has a tax-qualified tax-deferred

Subsequent Events

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events The Company has evaluated subsequent events from the balance sheet date through the date on which these financial statements were issued. Subsequent to the issuance of the financial statements, the following events occurred and required disclosure in, or revision to, the financial statements: On October 6, 2020, the Company completed the IPO, in which the Company issued and sold 5,800,000 shares of its common stock at a public offering price of $15.00 per share. On October 14, 2020, the Company sold an additional 757,991 shares of common stock at $15.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock. The total gross proceeds of the IPO were $98.4 million and the Company raised approximately $88.3 million in net proceeds after deducting underwriting discounts and commissions and offering expenses payable by the Company. Upon the closing of the IPO, all of the outstanding shares of Series A-1 On December 29, 2020, the Company entered into a lease agreement for approximately 33,518 square feet, or the Pod 4 Portion, and approximately 54,666 square feet, or the Pod 5 Portion, of a manufacturing facility located in Andover, Massachusetts. The lease contains a free rent period for each of the Pod 4 Portion and the Pod 5 Portion. The term of the lease will continue for 15 years from the date the monthly rent for the Pod 5 Portion commences, or approximately December 31, 2036, unless earlier terminated in accordance with the terms of the lease. The Company has two options to extend the term of the lease for the entire premises for a period of 10 years each, with rent during the extended term being based on the then-prevailing market rental rate. Under the lease, the monthly rent payments for the Pod 4 Portion are expected to commence on October 1, 2021, reflecting an approximately nine-month rent-free period following the execution of the lease. The Company has a right to occupy the Pod 4 Portion prior to the Pod 4 rent commencement date, subject to the completion of tenant improvements, and would be responsible for proportional base rent payments, utilities, and the Company’s proportionate share of operating costs and taxes attributable to the Pod 4 Portion, provided that such payments of base rent for the occupancy of the Pod 4 Portion would commence no earlier than July 1, 2021 in any event. Beginning on the Pod 4 rent commencement date, the Company will be obligated to make monthly base rent payments, which will initially be approximately $0.1 million and will increase to approximately $0.2 million during the initial term of the lease. The monthly rent payments for the Pod 5 Portion are expected to commence on January 1, 2022, reflecting an approximately one-year rent-free period following the execution of the lease. Beginning on the Pod 5 rent commencement date, the Company will be obligated to make monthly base rent payments, which will initially be approximately $0.2 million and will increase to approximately $0.3 million during the initial term of the lease. The total lease commitment is expected to be approximately $72.0 million over the 15-year	14. Subsequent Events The Company has completed an evaluation of all subsequent events after the audited balance sheet date of December 31, 2019 through July 29, 2020, the date the financial statements were issued except for Note 14(b) as to which the date is September 28, 2020. Subsequent to the issuance of the financial statements, the following events occurred and required disclosure in, or revision to, the financial statements: (a) Second Tranche of Series B Preferred Stock Financing (unaudited) In September 2020, the Company achieved certain milestones related to the clinical development of its lead product candidate, ONCR-177. One of those milestones was that the three patients in the first cohort and first patient in the second cohort of the Company’s Phase 1 trial experienced no dose limiting toxicities within the first 28 days following their initial doses of ONCR-177. Upon achievement of the milestones, the Series B investors became obligated to purchase additional shares of Series B in a second and final tranche closing (see Note 6 for additional information). On September 17 and 23, 2020, the Company issued an aggregate of 41,690,117 shares of Series B at $0.8597 per share, for gross proceeds to the Company of $35.8 million, at the second tranche closing. (b) Reverse Stock Split On September 23, 2020, the Company’s board of directors and stockholders approved a one-for-12.0874 reverse split of the Company’s issued and outstanding common stock and a proportional adjustment to the existing conversion ratios for the outstanding shares of convertible preferred stock, which became effective on September 25, 2020. Accordingly, all share and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect the reverse stock split, including reclassification of par, additional paid-in capital and accumulated deficit amounts as a result of the split adjustment. (c) Initial Public Offering (unaudited) On October 6, 2020, the Company completed the IPO, in which the Company issued and sold 5,800,000 shares of its common stock at a public offering price of $15.00 per share. On October 14, 2020, the Company sold an additional 757,991 shares of common stock at $15.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock. The total gross proceeds of the IPO were $98.4 million and the Company raised approximately $88.3 million in net proceeds after deducting underwriting discounts and commissions and offering expenses payable by the Company. Upon the closing of the IPO, all of the outstanding shares of Series A-1 (d) Other (unaudited) On September 23, 2020, the Company adopted the 2020 Equity Incentive Plan, or the 2020 Plan, which will become effective upon the execution of the underwriting agreement related to the IPO and will serve as the successor to the Plan. The 2020 Plan authorizes the award of stock options, restricted stock awards, or RSAs, stock appreciation rights, or SARs, restricted stock units, or RSUs, cash awards, performance awards and stock bonus awards. Under the 2020 Plan, 2,800,000 shares of common stock, plus any reserved shares not issued or subject to outstanding grants under the Plan on the effective date of the 2020 Plan are reserved for issuance pursuant to awards granted under the 2020 Plan. The number of shares reserved for issuance under the 2020 Plan will increase automatically on January 1 of each of 2021 through 2030 by the number of shares equal to the lesser of 5% of the aggregate number of outstanding shares of common stock as of the immediately preceding December 31, or a number as may be determined by the board of directors. On September 23, 2020, the Company adopted the 2020 Employee Stock Purchase Plan, or the ESPP, which will become effective upon the execution of the underwriting agreement related to the IPO. The Company has initially reserved 280,000 shares of common stock for sale under the ESPP. The aggregate number of shares reserved for sale under the ESPP will increase automatically on January 1st of each of the first ten calendar years after the first offering date by the number of shares equal to the lesser of 1% of the total outstanding shares of common stock as of the immediately preceding December 31 (rounded to the nearest whole share) or a fixed number, or a number of shares as may be determined by the board of directors in any particular year. On December 29, 2020, the Company entered into a lease agreement for approximately 33,518 square feet, or the Pod 4 Portion, and approximately 54,666 square feet, or the Pod 5 Portion, of a manufacturing facility located in Andover, Massachusetts. The lease contains a free rent period for each of the Pod 4 Portion and the Pod 5 Portion. The term of the lease will continue for 15 years from the date the monthly rent for the Pod 5 Portion commences, or approximately December 31, 2036, unless earlier terminated in accordance with the terms of the lease. The Company has two options to extend the term of the lease for the entire premises for a period of 10 years each, with rent during the extended term being based on the then-prevailing market rental rate. Under the lease, the monthly rent payments for the Pod 4 Portion are expected to commence on October 1, 2021, reflecting an approximately nine-month rent-free period following the execution of the lease. The Company has a right to occupy the Pod 4 Portion prior to the Pod 4 rent commencement date, subject to the completion of tenant improvements, and would be responsible for proportional base rent payments, utilities, and the Company’s proportionate share of operating costs and taxes attributable to the Pod 4 Portion, provided that such payments of base rent for the occupancy of the Pod 4 Portion would commence no earlier than July 1, 2021 in any event. Beginning on the Pod 4 rent commencement date, the Company will be obligated to make monthly base rent payments, which will initially be approximately $0.1 million and will increase to approximately $0.2 million during the initial term of the lease. The monthly rent payments for the Pod 5 Portion are expected to commence on January 1, 2022, reflecting an approximately one-year rent-free period following the execution of the lease. Beginning on the Pod 5 rent commencement date, the Company will be obligated to make monthly base rent payments, which will initially be approximately $0.2 million and will increase to approximately $0.3 million during the initial term of the lease. The total lease commitment is expected to be approximately $72.0 million over the 15-year

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
COVID-19 Pandemic	COVID-19 With the ongoing COVID-19 COVID-19 re-organized COVID-19 COVID-19
Basis of Presentation		Basis of Presentation These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and ASU of the FASB.
Principles of Consolidation	Principles of Consolidation The accompanying unaudited interim condensed consolidated financial statements of the Company include the accounts of its wholly owned subsidiary, Oncorus Securities Corporation. All intercompany transactions have been eliminated in consolidation. The Company has one operating segment.	Principles of Consolidation The accompanying consolidated financial statements of the Company include the accounts of its wholly owned subsidiary, Oncorus Securities Corporation. All intercompany transactions have been eliminated in consolidation. The Company has one operating segment.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, the estimated fair value of the Company’s common stock and share-based awards utilized for stock-based compensation purposes, the Company’s Series B tranche rights (see Note 5), accrued expenses, and amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, the estimated fair value of the Company’s common stock and share-based awards utilized for stock-based compensation purposes, the Company’s Series A-1
Classification and Measurement of Series A-1 and Series B Redeemable Convertible Preferred Stock	Classification and Measurement of Series A-1 Upon the closing of the IPO on October 6, 2020, all shares of preferred stock converted into common stock. Prior to the IPO, the Company classified its Series A-1 A-1”) A-1 A-1 A-1 480-10-S99. A-1 A-1
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	Deferred Rent The Company has received tenant improvement consideration from its landlord as well as free rental periods, each of which are amortized on a straight-line basis over the term of the lease.
Concentration of Credit Risk and of Significant Suppliers	Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all of its cash at one financial institution, that management believes to be of high credit quality, in amounts that exceed federally insured limits. Cash equivalents consist of money market funds that invest primarily in U.S. government-backed securities and treasuries. The Company is dependent upon a third-party contract manufacturer and third-party contract research organizations for the performance of portions of its testing for pre-clinical	Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all of its cash at one financial institution that management believes to be of high credit quality, in amounts that exceed federally insured limits. Cash equivalents consist of money market funds that invest primarily in U.S. government-backed securities and treasuries. The Company is dependent upon a third-party contract manufacturer and third-party contract research organizations for the performance of portions of its testing for pre-clinical
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1 Level 2 Level 3 To the extent a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s cash equivalents, classified within Level 1, are valued using net asset value per share for the money market funds. The tranche rights granted to the Series B stockholders (the “Series B Tranche Rights”) were classified within Level 3 of the fair value hierarchy because they were valued using significant inputs not observable in the market. The valuation of the tranche rights used assumptions the Company believed would be made by a market participant. The Company assessed these estimates on an ongoing basis as additional data impacting the assumptions was obtained. Refer to Note 5 for additional information regarding the valuation of the tranche rights. The Company believes that the carrying amounts of prepaid expenses, other current assets, accounts payable, and accrued expenses approximate their fair value due to the short-term nature of those instruments.
Research and Development Expense		Research and Development Expenses Research and development expenses are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including compensation-related expenses for research and development personnel, including stock-based compensation expense, preclinical and clinical activities, costs of manufacturing, overhead expenses including facilities and laboratory expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation and amortization. Upfront and annual license payments related to acquired technologies or technology licenses which have not yet reached technological feasibility and have no alternative future use are also included in research and development expense for the period in which they are incurred.
General and Administrative Expenses		General and Administrative Expenses General and administrative expenses consist primarily of salaries and related costs, including stock-based compensation expense, for personnel in executive, finance and accounting, business development, operations and administrative functions. General and administrative expenses also include fees for legal, consulting, accounting and audit services as well as insurance, outside service providers, direct and allocated facility-related costs and depreciation and amortization.
Interest Income on Investments		Interest Income on Investments Interest income is separately presented on the consolidated statements of operations and comprehensive loss and consists of interest on cash and cash equivalents.
Cash and Cash Equivalents		Cash and Cash Equivalents The primary objectives for the Company’s investment portfolio are the preservation of capital and maintenance of liquidity. The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. At December 31, 2018 and 2019, cash and cash equivalents include bank demand deposits and money market funds that invest primarily in U.S. government-backed securities and treasuries. Cash equivalents are stated at cost, which is substantially equivalent to fair value.
Property and Equipment, Net		Property and Equipment, Net Property and equipment are recorded at cost. Expenditures for major renewals or betterments that extend the useful lives of property and equipment are capitalized; expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related assets. Property and equipment are depreciated as follows: ASSET TYPE ESTIMATED USEFUL LIFE Computer equipment and software 3-5 years Furniture and fixtures 5 years Laboratory equipment 5 years Leasehold improvements Shorter of lease term or estimated useful life Upon retirement or sale, the cost and related accumulated depreciation and amortization of assets disposed of are removed from the accounts, and any resulting gain or loss is included in loss from operations as a component of other income (expense).
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review were to be performed to evaluate a long-lived asset for recoverability, the Company would compare forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized if estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: Level 1 Level 2 Level 3 To the extent a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s cash equivalents, classified within Level 1, are valued using net asset value per share for the money market funds. The Company’s Series A-1 on-going A-1 The Company believes that the carrying amounts of prepaid expenses, other current assets, accounts payable, and accrued expenses approximate their fair value due to the short-term nature of those instruments.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzes the progress of the studies, trials or other services performed, including invoices received and contracted costs. Judgments and estimates are made in determining the accrued expense balances at the end of each reporting period.	Research Contract Costs and Accruals The Company has entered into various research service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzes the progress of the studies, trials or other services performed, including invoices received and contracted costs. Judgments and estimates are made in determining the accrued expense balances at the end of each reporting period.
Deferred Rent	Deferred Offering Costs The Company capitalizes certain legal, professional, accounting and other third-party fees that are directly associated with in-process paid-in	Deferred Rent The Company has received tenant improvement consideration from its landlord as well as free rental periods, each of which are amortized on a straight-line basis over the term of the lease.
Patent Costs		Patent Costs The Company expenses patent costs as incurred and records such costs within general and administrative expenses.
Comprehensive Loss		Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ (deficit) equity that result from transactions and economic events other than those with stockholders. For all periods presented, net loss is the same as comprehensive loss as there are no comprehensive income items. Classification and Measurement of Series A-1 The Company has classified its Series A-1 A-1”) A-1 A-1 A-1 480-10-S99. A-1 Series A-1
Income Taxes		Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the consolidated financial statement and tax bases of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be realized and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The potential for recovery of deferred tax assets is evaluated by analyzing carryback capacity in periods with taxable income, reversal of existing taxable temporary differences and estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step more-likely-than-not
Stock-Based Compensation		Stock-Based Compensation The Company measures all stock options and other stock-based awards granted based on the fair value of the award on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has elected to recognize forfeitures as they occur. The reversal of compensation cost previously recognized for an award that is forfeited because of a failure to satisfy a service or performance condition is recognized in the period of the forfeiture. Generally, the Company issues stock options and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method over the requisite service period. In November 2018, the Company granted a performance-based option to an employee with a total fair value of $0.1 million. A portion of these options vested upon the closing of the Series B financing and stock compensation of $0.04 million was recorded in 2019 related to these vested options. The vesting condition for the remainder of these options was not considered probable and as a result, no stock-based compensation was recorded related to this portion of the award during the year ended December 31, 2019. Prior to the adoption of ASU No. 2018-07, Compensation—Stock Compensation non-employee non-employees No. 2018-07. The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company estimates the fair value of common stock using an appropriate valuation methodology, in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation The fair value of each stock option grant is estimated using the Black-Scholes option-pricing model. The Company is a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies within the biotechnology industry with characteristics similar to the Company. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is
Net Loss Per Share	Net Loss Per Share Net loss per share attributable to common stockholders is calculated using the two-class A-1 as-converted Diluted net loss per share is computed using the more dilutive of (a) the two-class if-converted A-1,	Net Loss Per Share Net loss per share attributable to common stockholders is calculated using the two-class A-1 as-converted Diluted net loss per share is computed using the more dilutive of (a) the two-class if-converted A-1,
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 equity issuances as deferred offering costs until such equity issuances are consummated. After consummation of the equity issuance, these costs are recorded as a reduction in the capitalized amount associated with the equity issuance. Should the equity issuance be delayed or abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss. During 2019, the Company incurred $1.5 million of deferred offering costs related to the Company’s proposed initial public offering (“IPO”). These offering costs were expensed at December 31, 2019 due to the expected timing of the Company’s proposed IPO.
Pro Forma Financial Information (unaudited)		Pro Forma Financial Information (unaudited) Upon the closing of a qualified IPO (as defined in the Company’s Certificate of Incorporation), all of the Company’s outstanding shares of Series A-1 A-1 A-1 A-1 Series A-1 A-1 The following table summarizes the Company’s unaudited pro forma net loss per share attributable to common stockholders (in thousands, except per share data): YEAR ENDED Numerator: Net loss attributable to common stockholders $ (34,991 ) Accretion of discount and dividends on redeemable convertible preferred stock 4,287 Pro forma net loss attributable to common stockholders $ (30,704 ) Denominator: Weighted average number of common shares outstanding 935 Pro forma weighted average shares outstanding after giving effect to the conversion of 8,225 Pro forma weighted average common shares outstanding 9,160 Pro forma basic and diluted net loss per share attributable to common stockholders, basic and diluted $ (3.35 ) In November 2018, the Company granted a performance-based stock option to an employee for which a portion of the vesting is triggered by completion of an IPO. The stock-based compensation expense related to the vesting of this performance award is not included in the pro forma amounts above as the impact would be immaterial.
Subsequent Events		Subsequent Events The Company considers events or transactions that occur after the balance sheet date but prior to the date the financial statements are issued for potential recognition or disclosure in the financial statements. The Company has completed an evaluation of all subsequent events after the audited balance sheet date of December 31, 2019 through the date the financial statements were issued, to ensure that these financial statements include appropriate disclosure of events both recognized in the financial statements as of December 31, 2019 and events which occurred subsequently but were not recognized in the financial statements. Refer to Note 14 for disclosure of material subsequent events.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use 2016-02, 2016-02 2016-02 right-to-use In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework 2018-13”), 2018-13 2018-13	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 will a right-of-use asset 2016-02, ASU 2016-02 is 2016-02 right-to-use In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework 2018-13”), 2018-13 2018-13

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Summary Of Estimated Useful Lives Of Property, Plant And Equipments	ASSET TYPE ESTIMATED USEFUL LIFE Computer equipment and software 3-5 years Furniture and fixtures 5 years Laboratory equipment 5 years Leasehold improvements Shorter of lease term or estimated useful life
Summary Of Net Loss Per Share Attributable To Common Stockholders	The following table summarizes the Company’s unaudited pro forma net loss per share attributable to common stockholders (in thousands, except per share data): YEAR ENDED Numerator: Net loss attributable to common stockholders $ (34,991 ) Accretion of discount and dividends on redeemable convertible preferred stock 4,287 Pro forma net loss attributable to common stockholders $ (30,704 ) Denominator: Weighted average number of common shares outstanding 935 Pro forma weighted average shares outstanding after giving effect to the conversion of 8,225 Pro forma weighted average common shares outstanding 9,160 Pro forma basic and diluted net loss per share attributable to common stockholders, basic and diluted $ (3.35 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 51,555 $ — $ — $ 51,555 $ 51,555 $ — $ — $ 51,555 FAIR VALUE MEASUREMENTS LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 38,430 $ — $ — $ 38,430 $ 38,430 $ — $ — $ 38,430 Liabilities: Series B tranche rights $ — $ — $ 1,876 $ 1,876 $ — $ — $ 1,876 $ 1,876	The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis (in thousands): FAIR VALUE MEASUREMENTS AS OF DECEMBER 31, 2018 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 19,881 $ — $ — $ 19,881 $ 19,881 $ — $ — $ 19,881 FAIR VALUE MEASUREMENTS AS OF DECEMBER 31, 2019 LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: Money market funds $ 38,430 $ — $ — $ 38,430 $ 38,430 $ — $ — $ 38,430 Liabilities: Series B tranche rights $ — $ — $ 1,876 $ 1,876 $ — $ — $ 1,876 $ 1,876

Property Plant And Equipment (T

Property Plant And Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
PropertyPlantAndEquipmentAbstract [Abstract]
Summary Of Property And Equipments,Net	Property and equipment, net as of December 31, 2018 and 2019 consisted of the following (in thousands): DECEMBER 31, 2018 2019 Laboratory equipment $ 2,514 $ 3,144 Computer equipment and software 41 114 Furniture and fixtures 159 313 Leasehold improvements 3,427 3,427 Fixed assets not yet placed in service — 328 6,141 7,326 Less accumulated depreciation (1,841 ) (2,851 ) Total property and equipment, net $ 4,300 $ 4,475

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Summary of Accrued Expenses	At September 30, 2020 and December 31, 2019, accrued expenses consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued research and development costs $ 890 $ 1,614 Accrued compensation 901 961 Accrued professional fees 1,176 564 Miscellaneous accrued expenses 188 382 Total accrued expenses $ 3,155 $ 3,521	At December 31, 2018 and 2019, accrued expenses consisted of the following (in thousands): AS OF DECEMBER 31, 2018 2019 Accrued research and development costs $ 466 $ 1,614 Accrued compensation 617 961 Accrued professional fees 114 564 Miscellaneous accrued expenses 93 382 Total accrued expenses $ 1,290 $ 3,521

Series A-1 and Series B Tranc_2

Series A-1 and Series B Tranche Rights (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Series A-1 and Series B Tranche Rights liability	A rollforward of the Series B Tranche Rights liability for the nine months ended September 30, 2020 is as follows (in thousands): SERIES B Balance at December 31, 2019 $ 1,876 Change in fair value 11,256 Reclassification of Series B Tranche Rights upon settlement (13,132 ) Balance at September 30, 2020 $ —	A rollforward of the Series A-1 and Series B Tranche Rights liability for the years ended December 31, 2018 and 2019 is as follows (in thousands): SERIES A-1 SERIES B Balance at December 31, 2017 $ 363 $ — Change in fair value (363 ) — Balance at December 31, 2018 — — Change in fair value — — Issuance of Series B tranche rights liability — 1,876 Balance at December 31, 2019 $ — $ 1,876

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Summary of Non-vested Restricted Stock Activity	A summary of non-vested AMOUNT WEIGHTED-AVERAGE Balance at December 31, 2019 41,602 $ 1.57 Repurchases — — Issuances — — Vested (19,197 ) 1.57 Balance at September 30, 2020 22,405 $ 1.57	A summary of non-vested AMOUNT WEIGHTED-AVERAGE Balance at December 31, 2018 154,590 $ 1.57 Repurchases (41,676 ) 1.57 Issuances — — Vested (71,312 ) 1.57 Balance at December 31, 2019 41,602 $ 1.57
Summary of Reserved Shares of Common Stock	The Company had reserved shares of common stock for the conversion or exercise of the following securities: SEPTEMBER 30, Conversion of Series A-1 6,328,894 Conversion of Series B 8,622,625 Exercise of Common Stock Warrants 71,544 Exercise of options to purchase common stock 2,109,151 Vesting of restricted stock 22,405 Shares available for issuance under the 2016 Plan 19,048 Total 17,173,667	The Company has reserved shares of common stock for the conversion or exercise of the following securities: DECEMBER 31, Conversion of Series A-1 6,328,894 Conversion of Series B 5,173,569 Exercise of common stock warrants 71,544 Exercise of options to purchase common stock 1,991,066 Vesting of restricted stock 41,602 Shares available for issuance under the Plan 201,224 Total 13,807,899

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Summary of fair valuation assumptions of option awards		The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the range of assumptions for the years ended December 31, 2018 and 2019 as noted in the following table: YEARS ENDED DECEMBER 31, 2018 2019 Expected volatility 71.4%-77.7% 77.0%-78.7% Expected dividends 0.0% 0.0% Expected term (in years) 6.1-10 6.1-10 Risk-free rate 2.8%-3.2% 1.4%-2.4%
Summary of Total Stock-based Compensation Including Both Stock Option Awards And Restricted Stock	Total stock-based compensation (including both stock option awards and restricted stock awards) was as follows: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 (in thousands) General and administrative $ 172 $ 112 $ 512 $ 255 Research and development 168 89 447 156 Total stock-based compensation $ 340 $ 201 $ 959 $ 411 Total stock-based compensation by award type was as follows: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 (in thousands) Restricted stock $ 8 $ 27 $ 24 $ 89 Stock options 332 174 935 322 Total stock-based compensation $ 340 $ 201 $ 959 $ 411	Total stock-based compensation (including both stock option awards and restricted stock) was as follows: YEARS ENDED DECEMBER 31, 2018 2019 (in thousands) General and administrative $ 207 $ 361 Research and development 119 350 Total stock-based compensation $ 326 $ 711 Total stock-based compensation by award type was as follows: YEARS ENDED DECEMBER 31, 2018 2019 (in thousands) Restricted stock $ 199 $ 116 Stock options 127 595 Total stock-based compensation $ 326 $ 711
Summary of Option Activity	A summary of option activity is presented below: SHARES WEIGHTED WEIGHTED- AGGREGATE Outstanding at December 31, 2019 1,991,066 $ 3.41 Granted 182,147 7.47 Exercised (64,062 ) 1.70 Canceled, expired or forfeited — — Outstanding at September 30, 2020 2,109,151 $ 3.81 8.4 $ 23,604 Vested at September 30, 2020 791,272 $ 2.70 7.8 $ 9,736	A summary of option activity under the Plan is presented below: SHARES WEIGHTED- AVERAGE WEIGHTED- AVERAGE AGGREGATE Outstanding at December 31, 2018 970,027 $ 1.74 Granted 1,109,073 4.74 Exercised (36,012 ) 1.62 Canceled, expired or forfeited (52,022 ) 2.14 Outstanding at December 31, 2019 1,991,066 $ 3.41 9.0 $ 6,696 Vested at December 31, 2019 455,449 $ 1.72 7.9 $ 2,301

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Summary of reconciliation of income tax expense(benefit) at the statutory federal income tax rate	A reconciliation of income tax expense (benefit) at the statutory federal income tax rate and income taxes as reflected in the consolidated financial statements is as follows: DECEMBER 31, 2018 2019 Federal income tax benefit at statutory rate 21.0 % 21.0 % State income tax, net of federal benefit 6.3 6.1 Permanent differences 0.2 (0.3 ) Research and development credit benefit 3.4 5.1 Change in valuation allowance (30.9 ) (31.9 ) Effective income tax rate — % — %
Summary of deferred tax assets and liabilities	The Company had a net loss for 2018 and 2019 and no income tax benefit has been recorded due to the full valuation allowance. The components of the Company’s deferred taxes at December 31, 2018 and 2019 are as follows (in thousands):​​​​​​​ DECEMBER 31, 2018 2019 Deferred tax assets: Net operating loss carryforwards (federal and state) $ 9,864 $ 18,070 Tax credits (federal and state) 1,630 3,129 Accrued expenses and other liabilities 164 156 Capitalized research and development expenditures 835 835 Accrued landlord incentive 537 430 Stock based compensation — 88 13,030 22,708 Valuation allowance (12,417 ) (22,201 ) Deferred tax liabilities: Fixed assets (613 ) (507 ) (613 ) (507 ) Net deferred tax assets $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments	Future minimum lease payments for the Company’s operating leases as of September 30, 2020 were as follows (in thousands): YEARS ENDING DECEMBER 31, 2020 (three months remaining) $ 370 2021 1,523 2022 1,569 2023 1,616 2024 48 $ 5,126	Future minimum lease payments for the Company’s operating leases as of December 31, 2019 were as follows (in thousands): YEARS ENDING DECEMBER 31, 2020 $ 1,479 2021 1,523 2022 1,569 2023 1,616 2024 48 $ 6,235

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Summary of Antidilutive Securities Excluded From Computation of Earnings Per Share	The following securities that could potentially dilute basic net loss per share in the future were not included in the computation of diluted net loss per share for the periods presented, because to do so would have been antidilutive: THREE MONTHS ENDED NINE MONTHS ENDED 2020 2019 2020 2019 Series A-1 6,328,894 6,328,894 6,328,894 6,328,894 Series B 8,622,625 4,590,404 8,622,625 4,590,404 Outstanding stock options 2,109,151 1,936,493 2,109,151 1,936,493 Restricted stock 22,405 57,828 22,405 57,828 Common stock warrants 71,544 71,544 71,544 71,544 Total 17,154,619 12,985,163 17,154,619 12,985,163	The following securities that could potentially dilute basic net loss per share in the future were not included in the computation of diluted net loss per share for the periods presented, because to do so would have been antidilutive: YEARS ENDED 2018 2019 Series A-1 6,328,894 6,328,894 Series B — 5,173,569 Outstanding stock options 970,027 1,991,066 Restricted stock 154,590 41,602 Common stock warrants 71,544 71,544 Total 7,525,055 13,606,675

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Oct. 14, 2020	Oct. 06, 2020	Sep. 25, 2020	Sep. 23, 2020	Jul. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Line Items]
Reverse stock split description			one-for-12.0874	one-for-12.0874
Preferred stock, shares outstanding						0				0
Common stock, shares authorized						227,000,000				227,000,000		227,000,000	107,000,000
Common stock, par or stated value per share						$ 0.0001				$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock, par or stated value per share						$ 0.0001				$ 0.0001
Accumulated deficit						$ (118,257)				$ (118,257)		$ (74,297)	$ (40,983)
Net loss						(19,531)	$ (7,573)	$ (17,201)	$ (14,264)	(36,732)	$ (21,837)	(30,704)	(18,046)
Cash and cash equivalents					$ 45,300	$ 54,019	$ 48,050			$ 54,019	$ 48,050	$ 45,286	$ 20,079	$ 13,031
Series B Preferred Stock [Member]
Accounting Policies [Line Items]
Additional paid in capital preferred stock					$ 35,800
Common Stock [Member]
Accounting Policies [Line Items]
Convertible preferred stock, shares						14,951,519				14,951,519
Subsequent event [Member]
Accounting Policies [Line Items]
Gross proceeds from issuance initial public offering	$ 98,400
Proceeds from issuance of initial public offer	$ 88,300
Preferred stock, shares outstanding		0
Common stock, shares authorized	100,000,000
Preferred stock, shares authorized	10,000,000	10,000,000
Common stock, par or stated value per share	$ 0.0001
Preferred stock, par or stated value per share	$ 0.0001	$ 0.0001
Subsequent event [Member] | Common Stock [Member]
Accounting Policies [Line Items]
Convertible preferred stock, shares		14,951,519
Subsequent event [Member] | IPO [Member]
Accounting Policies [Line Items]
Stock issued during period, shares, new issues		5,800,000
Share issue price		$ 15
Subsequent event [Member] | Over-Allotment Option [Member]
Accounting Policies [Line Items]
Stock issued during period, shares, new issues	757,991
Share issue price	$ 15

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Deferred offering costs	$ 1.5	$ 1.5

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary Of Estimated Useful Lives Of Property, Plant And Equipments (Detail)	12 Months Ended
	Dec. 31, 2019
Computer Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	5 years
Computer Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member]
Property, Plant and Equipment, Useful Life	5 years
Laboratory equipment [Member]
Property, Plant and Equipment, Useful Life	5 years
Leaseholds and Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Estimated Useful Lives	Shorter of lease term or estimated useful life

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Pro Forma Financial Information (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss attributable to common stockholders	$ (19,531)	$ (7,573)	$ (17,201)	$ (14,264)	$ (36,732)	$ (21,837)	$ (30,704)	$ (18,046)
Accretion of discount and dividends on redeemable convertible preferred stock	2,848	1,578			8,298	1,609	4,287	98
Pro forma net loss attributable to common stockholders	$ (22,379)	$ (9,151)			$ (45,030)	$ (23,446)	$ (34,991)	$ (18,144)
Denominator:
Weighted average number of common shares outstanding	1,030,000	946,000			1,010,000	920,000	935,000	793,000
Pro forma weighted average shares outstanding after giving effect to the conversion of redeemable convertible preferred stock							8,225,000
Pro forma weighted average common shares outstanding	1,030,000	946,000			1,010,000	920,000	935,000	793,000
Pro forma basic and diluted net loss per share attributable to common stockholders, basic and diluted	$ (21.73)	$ (9.67)			$ (44.58)	$ (25.48)	$ (37.42)	$ (22.88)
Pro Forma [Member]
Numerator:
Pro forma net loss attributable to common stockholders							$ (30,704)
Denominator:
Weighted average number of common shares outstanding							9,160,000
Pro forma weighted average common shares outstanding							9,160,000
Pro forma basic and diluted net loss per share attributable to common stockholders, basic and diluted							$ (3.35)

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value On a Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 51,555	$ 38,430	$ 19,881
Liabilities		1,876
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	51,555	38,430	19,881
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities		1,876
Series B tranche rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities		1,876
Series B tranche rights [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities		1,876
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	51,555	38,430	19,881
Money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 51,555	$ 38,430	$ 19,881

Property Plant And Equipment -

Property Plant And Equipment - Additional Details (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment Additional Details [Abstract]
Depreciation expense	$ 983	$ 786	$ 1,071	$ 956

Property Plant And Equipment _2

Property Plant And Equipment - Property and equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 7,326	$ 6,141
Less accumulated depreciation		2,851	1,841
Total property and equipment, net	$ 4,506	4,475	4,300
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		3,144	2,514
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		114	41
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		313	159
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		3,427	$ 3,427
Fixed assets not yet placed in service [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 328

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued research and development costs	$ 890	$ 1,614	$ 466
Accrued compensation	901	961	617
Accrued professional fees	1,176	564	114
Miscellaneous accrued expenses	188	382	93
Total accrued expenses	$ 3,155	$ 3,521	$ 1,290

Series A-1 and Series B Tranc_3

Series A-1 and Series B Tranche Rights - Summary of Series A-1 and Series B Tranche Rights Liability (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 1,876
Reclassification of Series B Tranche Rights liability upon settlement	(35,826)	$ (47,303)	$ (53,328)
Ending Balance			1,876
Series B tranche rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	1,876
Change in fair value	11,256
Reclassification of Series B Tranche Rights liability upon settlement	(13,132)
Ending Balance			1,876
Series A-1 Tranche Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 1,876			$ 363
Change in fair value				$ (363)
Reclassification of Series B Tranche Rights liability upon settlement			(1,876)
Ending Balance			$ 1,876

Series A-1 and Series B Tranc_4

Series A-1 and Series B Tranche Rights - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 01, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from issuance of Series B preferred stock and tranche liability					$ 35,826	$ 47,303	$ 53,328
Fair value adjustments of rights liability			$ 10,631		11,256			$ (363)
Series B Tranche Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from issuance of Series B preferred stock and tranche liability					13,132
Settlement of Series B tranche rights liability					$ 13,100
Warrant liability fair value per share		$ 1.18	$ 1.18		$ 1.18
Fair value adjustments of rights liability			$ 10,600
Series B Tranche Rights [Member] | Measurement Input, Discount Rate [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and rights outstanding measurement		0.20%	0.20%		0.20%		1.60%
Series B Tranche Rights [Member] | Measurement Input, Discount Rate [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and rights outstanding measurement		1.90%	1.90%		1.90%		1.90%
Series B Tranche Rights [Member] | Measurement Input Probability Of Achievement [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and rights outstanding measurement		85.00%	85.00%		85.00%		85.00%
Series B Tranche Rights [Member] | Measurement Input Probability Of Achievement [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and rights outstanding measurement		90.00%	90.00%		90.00%
Series B [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of Series B preferred stock (Shares)			41,690,117	55,486,215			62,535,183
Share price		$ 0.8597	$ 0.8597		$ 0.8597		$ 0.8597		$ 0.8597
Settlement of Series B tranche rights liability			$ 13,132
Series B [Member] | Tranche Two [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of Series B preferred stock (Shares)		41,690,117	41,690,177		41,690,117		41,690,117
Share price	$ 0.8597	$ 0.8597	$ 0.8597		$ 0.8597		$ 0.8597
Proceeds from issuance of Series B preferred stock and tranche liability	$ 35,800				$ 35,800		$ 35,800

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional information (Detail) $ / shares in Units, $ in Thousands	Oct. 14, 2020USD ($)$ / sharesshares	Oct. 06, 2020$ / sharesshares	Sep. 17, 2020USD ($)$ / sharesshares	Sep. 01, 2020USD ($)$ / shares	Nov. 27, 2019USD ($)shares	Sep. 06, 2018$ / sharesshares	Oct. 27, 2016USD ($)$ / sharesshares	Jul. 11, 2016USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Aug. 27, 2019USD ($)shares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019shares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)shares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Jun. 30, 2020shares	Nov. 30, 2019shares	Aug. 31, 2019$ / sharesshares	Jun. 30, 2019shares	Dec. 31, 2017shares
Redeemable Noncontrolling Interest [Line Items]
Preferred stock, par or stated value per share | $ / shares									$ 0.0001				$ 0.0001		$ 0.0001
Proceeds from issuance of Series B preferred stock and tranche liability | $															$ 35,826	$ 47,303	$ 53,328
Payments of stock issuance costs | $															$ 563
Preferred stock dividend per share | $ / shares																	$ 0.064
Preferred stock, shares outstanding									0				0		0
Proceeds from issuance of series A-1 preferred stock and tranche liability | $															$ 35,826	$ 47,303	$ 53,328
Warrants or rights, number of shares called									71,544				71,544		71,544		71,544
Common Stock Warrants [Member]
Redeemable Noncontrolling Interest [Line Items]
Exercise price of warrants | $ / shares									$ 1.21			$ 1.21	$ 1.21		$ 1.21		$ 1.21
Warrants or rights, number of shares called									71,544			57,239	71,544		71,544		71,544
Series A-1 Tranche Rights [Member]
Redeemable Noncontrolling Interest [Line Items]
Proceeds from issuance of Series B preferred stock and tranche liability | $																	$ 1,876
Proceeds from issuance of series A-1 preferred stock and tranche liability | $																	$ 1,876
Common Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Convertible preferred stock, shares									14,951,519				14,951,519		14,951,519
Subsequent Event [Member]
Redeemable Noncontrolling Interest [Line Items]
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, par or stated value per share | $ / shares	$ 0.0001	$ 0.0001
Issuance of Series B preferred stock (Shares)			41,690,117
Share price | $ / shares			$ 0.8597
Proceeds from issuance of Series B preferred stock and tranche liability | $			$ 35,800
Gross proceeds from issuance initial public offering | $	$ 98,400
Preferred stock, shares outstanding		0
Issuance of series A-1 preferred stock(shares)			41,690,117
Issuance of series A-2 preferred stock(shares)			41,690,117
Proceeds from issuance of series A-1 preferred stock and tranche liability | $			$ 35,800
Subsequent Event [Member] | Common Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Convertible preferred stock, shares		14,951,519
Subsequent Event [Member] | Minimum [Member]
Redeemable Noncontrolling Interest [Line Items]
Gross proceeds from issuance initial public offering | $	50,000
Market capitalization | $	$ 200,000
Redeemable Convertible Preferred Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Temporary equity, shares authorized									180,725,292				180,725,292		180,725,292		180,725,292
Temporary equity, par value | $ / shares									$ 0.0001				$ 0.0001		$ 0.0001		$ 0.0001
Temporary equity, liquidation preference per share | $ / shares									$ 0.80				$ 0.80		$ 0.80
Preferred stock voting rights															Each share of Series B and Series A-1 were entitled to the number of votes equal to the number of shares of common stock into which each share of Series B and Series A-1 were convertible at the time of such vote.		Each share of Series B and Series A-1 are entitled to the number of votes equal to the number of shares of common stock into which each share of Series B and Series A-1 are convertible at the time of such vote.
Redeemable Convertible Preferred Stock [Member] | Subsequent Event [Member]
Redeemable Noncontrolling Interest [Line Items]
Preferred stock, conversion ratio		0.0827
Series A One Redeemable Convertible Preferred Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Temporary equity, shares authorized									76,500,000				76,500,000		76,500,000		76,500,000	77,000,000
Temporary equity, par value | $ / shares									$ 0.0001				$ 0.0001		$ 0.0001		$ 0.0001	$ 0.0001
Temporary equity, shares issued									76,500,000				76,500,000		76,500,000		76,500,000	76,500,000
Temporary equity, shares outstanding									76,499,992				76,499,992	76,499,992	76,499,992	76,499,992	76,499,992	76,499,992	76,499,992			76,499,992	46,068,750
Convertible preferred stock, shares									6,328,894				6,328,894		6,328,894		6,328,894
Issuance of Series B preferred stock (Shares)																		30,599,992
Share price | $ / shares									$ 0.80				$ 0.80		$ 0.80		$ 0.80
Temporary equity, liquidation preference | $									$ 68,436				$ 68,436		$ 68,436		$ 63,739	$ 63,739
Minimum outstanding shares required for voting rights									2,250,000				2,250,000		2,250,000		2,250,000
Preferred stock dividend per share | $ / shares															$ 0.064
Issuance of series A-1 preferred stock(shares)																		30,599,992
Issuance of series A-2 preferred stock(shares)																		30,599,992
Series A One Redeemable Convertible Preferred Stock [Member] | Tranche One [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)								21,165,626
Share price | $ / shares								$ 1.04
Issuance of series A-1 preferred stock(shares)								21,165,626
Issuance of series A-2 preferred stock(shares)								21,165,626
Series A One Redeemable Convertible Preferred Stock [Member] | Series A-1 Tranche Rights [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)							1,500,000	16,137,499			22,665,626	4,612,500
Share price | $ / shares						$ 0.80	$ 0.80	$ 0.80			$ 0.80	$ 1
Proceeds from issuance of Series B preferred stock and tranche liability | $							$ 1,200	$ 12,900			$ 18,100	$ 4,600
Payments of stock issuance costs | $												$ 400
Issuance of series A-1 preferred stock(shares)							1,500,000	16,137,499			22,665,626	4,612,500
Issuance of series A-2 preferred stock(shares)							1,500,000	16,137,499			22,665,626	4,612,500
Proceeds from issuance of series A-1 preferred stock and tranche liability | $							$ 1,200	$ 12,900			$ 18,100	$ 4,600
Purchase of series A-1 preferred stock(shares)						30,599,992
Convertible securities, conversion ratio								1.25
Series A One Redeemable Convertible Preferred Stock [Member] | Investors [Member]
Redeemable Noncontrolling Interest [Line Items]
Temporary equity, shares outstanding						168,750
Convertible preferred stock, shares						13,959
Series A One Redeemable Convertible Preferred Stock [Member] | Tranche One [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)								22,086,537
Issuance of series A-1 preferred stock(shares)								22,086,537
Issuance of series A-2 preferred stock(shares)								22,086,537
Series B Redeemable Convertible Preferred Stock [Member]
Redeemable Noncontrolling Interest [Line Items]
Temporary equity, shares authorized									104,225,000				104,225,000		104,225,000		104,225,000	0			92,477,021
Temporary equity, par value | $ / shares									$ 0.0001				$ 0.0001		$ 0.0001		$ 0.0001	$ 0.0001
Temporary equity, shares issued									104,225,000				104,225,000		104,225,000		62,535,000	0
Temporary equity, shares outstanding									104,225,000				104,225,000	55,486,215	104,225,000	55,486,215	62,535,000	0	62,535,183
Convertible preferred stock, shares									8,622,625				8,622,625		8,622,625		5,173,569
Preferred stock, shares authorized																	104,225,300
Issuance of Series B preferred stock (Shares)													41,690,117	55,486,215			62,535,183
Share price | $ / shares									$ 0.8597				$ 0.8597		$ 0.8597		$ 0.8597				$ 0.8597
Temporary equity, additional shares authorized																				11,748,279
Payments of stock issuance costs | $					$ 400
Temporary equity, liquidation preference | $									$ 94,492				$ 94,492		$ 94,492		$ 55,326	$ 55,326
Preferred stock, conversion basis															one share of common stock for every 10 shares of Series B		one share of common stock for every 10 shares of Series B.
Preferred stock dividend per share | $ / shares															$ 0.06877		$ 0.06877
Issuance of series A-1 preferred stock(shares)													41,690,117	55,486,215			62,535,183
Issuance of series A-2 preferred stock(shares)													41,690,117	55,486,215			62,535,183
Series B Redeemable Convertible Preferred Stock [Member] | Tranche One [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)					7,048,968
Proceeds from issuance of Series B preferred stock and tranche liability | $					$ 6,100					$ 47,700
Issuance of series A-1 preferred stock(shares)					7,048,968
Issuance of series A-2 preferred stock(shares)					7,048,968
Proceeds from issuance of series A-1 preferred stock and tranche liability | $					$ 6,100					$ 47,700
Series B Redeemable Convertible Preferred Stock [Member] | Subsequent Event [Member] | Minimum [Member]
Redeemable Noncontrolling Interest [Line Items]
Percentage of consent or vote required for conversion of preferred Shares		68.00%
Series B Redeemable Convertible Preferred Stock [Member] | Tranche One [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)					7,048,968					55,486,215
Share price | $ / shares																					$ 0.8597
Proceeds from issuance of Series B preferred stock and tranche liability | $					$ 6,100					$ 47,700
Issuance of series A-1 preferred stock(shares)					7,048,968					55,486,215
Issuance of series A-2 preferred stock(shares)					7,048,968					55,486,215
Proceeds from issuance of series A-1 preferred stock and tranche liability | $					$ 6,100					$ 47,700
Series B Redeemable Convertible Preferred Stock [Member] | Tranche Two [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)									41,690,117				41,690,177		41,690,117		41,690,117
Share price | $ / shares				$ 0.8597					$ 0.8597				$ 0.8597		$ 0.8597		$ 0.8597
Proceeds from issuance of Series B preferred stock and tranche liability | $				$ 35,800											$ 35,800		$ 35,800
Issuance of series A-1 preferred stock(shares)									41,690,117				41,690,177		41,690,117		41,690,117
Issuance of series A-2 preferred stock(shares)									41,690,117				41,690,177		41,690,117		41,690,117
Proceeds from issuance of series A-1 preferred stock and tranche liability | $				$ 35,800											$ 35,800		$ 35,800
Series A Two Redeemable Convertible Preferred Stock [Member] | Series A-2 Tranche Rights [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of Series B preferred stock (Shares)							1,538,462
Share price | $ / shares							$ 1.04
Issuance of series A-1 preferred stock(shares)							1,538,462
Issuance of series A-2 preferred stock(shares)							1,538,462

Common Stock - Summary of Non-V

Common Stock - Summary of Non-Vested Restricted Stock Activity (Detail) - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested	20,000	90,000	100,000	200,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at December 31, 2019	41,602	154,590	154,590
Repurchases			(41,676)
Vested	19,197		71,312
Balance at September 30, 2020	22,405		41,602	154,590
Balance at December 31, 2019	$ 1.57	$ 1.57	$ 1.57
Repurchases			1.57
Vested	1.57		1.57
Balance at September 30, 2020	$ 1.57		$ 1.57	$ 1.57

Common Stock - Summary of Reser

Common Stock - Summary of Reserved Shares of Common Stock (Detail) - shares	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Exercise of Common Stock Warrants	71,544	71,544
Exercise of options to purchase common stock	2,109,151	1,991,066	970,027
Shares available for issuance under the 2016 Plan	19,048	201,224
Total	17,173,667	13,807,899
Exercise of options to purchase common stock [Member]
Exercise of options to purchase common stock	2,109,151	1,991,066
Restricted Stock [Member]
Vesting of restricted stock	22,405	41,602	154,590
Conversion of Series A-1 [Member]
Conversion of Series	6,328,894	6,328,894
Conversion of Series B [Member]
Conversion of Series	8,622,625	5,173,569

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Oct. 14, 2020	Dec. 31, 2018	Mar. 31, 2016
Common stock, voting rights	Each share of common stock is entitled to one vote.	Each share of common stock is entitled to one vote
Common stock, shares authorized	227,000,000	227,000,000		107,000,000
Common stock, par or stated value per share	$ 0.0001	$ 0.0001		$ 0.0001
Warrants or rights, number of shares called	71,544	71,544
Common Stock Warrants [Member]
Warrants or rights, number of shares called	71,544	71,544			57,239
Warrants or rights, exercise price	$ 1.21	$ 1.21			$ 1.21
Restricted Stock [Member] | Founders [Member]
Share-based payment award, award vesting percentage	25.00%	25.00%
Share based payment award, award vesting period	4 years	4 years
Subsequent Event [Member]
Common stock, shares authorized			100,000,000
Common stock, par or stated value per share			$ 0.0001

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary Of Fair Valuation Assumptions Of Option Awards (Detail) - Option Pricing Model [Member]	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividends	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	77.00%	71.40%
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Risk-free rate	1.40%	2.80%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	78.70%	77.70%
Expected term (in years)	10 years	10 years
Risk-free rate	2.40%	3.20%

Equity Incentive Plan - Summa_2

Equity Incentive Plan - Summary of Total Stock-based Compensation Including Both Stock Option Awards And Restricted Stock (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expenses	$ 340	$ 201	$ 959	$ 411	$ 711	$ 326
Restricted Stock [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expenses	8	27	24	89	116	199
Stock options [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expenses	332	174	935	322	595	127
General and administrative [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expenses	172	112	512	255	361	207
Research and development [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expenses	$ 168	$ 89	$ 447	$ 156	$ 350	$ 119

Equity Incentive Plan - Additio

Equity Incentive Plan - Additional Information (Detail) - USD ($)	Jan. 01, 2021	Sep. 30, 2020	Sep. 23, 2020	Sep. 01, 2019	Nov. 30, 2018	Mar. 31, 2016	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		17,173,667						17,173,667		17,173,667		13,807,899
Aggregate number of outstanding shares of common stock			1.00%
Share based payment awards options granted										182,147		1,109,073
Share based compensation expenses								$ 340,000	$ 201,000	$ 959,000	$ 411,000	$ 711,000	$ 326,000
Fair value of restricted shares vested										20,000	90,000	100,000	200,000
Common stock reserved for future issuance		19,048						19,048		19,048		201,224
Share based compensation options vested							21,485
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expenses								$ 8,000	$ 27,000	$ 24,000	$ 89,000	$ 116,000	$ 199,000
Fair value of restricted shares vested										19,197		71,312
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment awards options granted		363,150
Share based compensation expenses		$ 0										$ 0
Weighted average grant date fair value of options granted										$ 5.36	$ 3.24	$ 3.26	$ 1.21
Unrecognized compensation expense related to stock options		$ 3.8						$ 3.8		$ 3.8		$ 3.7
Unrecognized compensation expense related to stock options weighted average period										3 years		3 years 6 months
2016 Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance						2,736,105
Share based payment awards options granted				28,647	85,943
Share based payment awards vestings rights description					This grant is included in the outstanding options in the summary table below. Vesting of the option is based on certain performance criteria and shall vest as follows: (i) 16.66% of the shares vested upon the first closing of the Company’s Series B stock financing, (ii) 33.33% of the shares vest in 24 equal monthly installments beginning with the first month following the initial closing of the Series B stock financing, (iii) 25% of the shares vest on the date immediately prior to an IPO of the Company’s equity securities and (iv) 25% of the shares vest in 24 equal monthly installments beginning with the first month following the IPO.
Common stock reserved for future issuance		19,048						19,048		19,048		201,224
Share based compensation options vested				14,323
2016 Plan [Member] | Restricted Stock [Member] | Share-based payment arrangement, tranche one [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment awards vestings rights					16.66%
2016 Plan [Member] | Restricted Stock [Member] | Share-based payment arrangement, tranche two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment awards vestings rights					33.33%
2016 Plan [Member] | Restricted Stock [Member] | Share-based payment arrangement, tranche three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment awards vestings rights					25.00%
2016 Plan [Member] | Restricted Stock [Member] | Share-based payment arrangement, tranche four [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment awards vestings rights					25.00%
2016 Plan [Member] | Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period						4 years
2016 Plan [Member] | Restricted Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period						3 years
2020 Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance			2,800,000
Share based payment award description			The number of shares reserved for issuance under the 2020 Plan will increase automatically on January 1 of each of 2021 through 2030 by the number of shares equal to the lesser of 5% of the aggregate number of outstanding shares of common stock as of the immediately preceding December 31, or a number as may be determined by the board of directors.
Aggregate number of outstanding shares of common stock	5.00%
Employee stock purchase plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance			280,000
Share based payment award description			The aggregate number of shares reserved for sale under the ESPP will increase automatically on January 1st of each fiscal year starting on January 1, 2021 and ending on and including January 1, 2030, by the number of shares equal to the lesser of (a) 1% of the total number of shares of common stock outstanding on the last day of the fiscal year prior to the date of such automatic increase and (b) 560,000 shares, provided that prior to the date of any such increase, the board of directors may determine a less number of shares for such increase.
Share based payments shares increase decrease			560,000

Equity Incentive Plan - Summa_3

Equity Incentive Plan - Summary of Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Shares, Outstanding	1,991,066	970,027
Shares, Granted	182,147	1,109,073
Shares, Exercised	64,062	36,012
Shares, Canceled, expired or forfeited		52,022
Shares, Outstanding	2,109,151	1,991,066
Shares, Vested	791,272	455,449
Weighted average exercise price	$ 3.41	$ 1.74
Weighted average exercise price, Granted	7.47	4.74
Weighted average exercise price, Exercised	1.70	1.62
Weighted average exercise price, Expired or forfeited		2.14
Weighted average exercise price, Outstanding	3.81	3.41
Weighted average exercise price, Vested	$ 2.70	$ 1.72
Weighted- Average remaining contractual term (years), Outstanding	8 years 4 months 24 days	9 years
Weighted- Average remaining contractual term (years), Vested	7 years 9 months 18 days	7 years 10 months 24 days
Aggregate intrinsic value, Outstanding	$ 23,604	$ 6,696
Aggregate intrinsic value, Vested	$ 9,736	$ 2,301

Income Taxes - Summary Of Recon

Income Taxes - Summary Of Reconciliation Of Income Tax Expense(Benefit) At The Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal income tax benefit at statutory rate	21.00%	21.00%
State income tax, net of federal benefit	6.10%	6.30%
Permanent differences	(0.30%)	0.20%
Research and development credit benefit	5.10%	3.40%
Change in valuation allowance	(31.90%)	(30.90%)
Effective income tax rate	0.00%	0.00%

Income Taxes - Summary Of Defer

Income Taxes - Summary Of Deferred Tax Assets And Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carry forwards (federal and state)	$ 18,070	$ 9,864
Tax credits (federal and state)	3,129	1,630
Accrued expenses and other liabilities	156	164
Capitalized research and development expenditures	835	835
Accrued landlord incentive	430	537
Stock based compensation	88	0
Total Deferred tax assets	22,708	13,030
Valuation allowance	22,201	12,417
Deferred tax liabilities:
Fixed assets	507	613
Total Deferred tax liabilities	507	613
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ (22,201,000)	$ (12,417,000)
Increase in valuation allowance	9,800,000
Net operating loss carry forward for federal income tax purpose	66,400,000
Net opertaing loss carryforward for state income tax purpose	65,300,000
Deferred tax assets, research and development costs	835,000	835,000
Unrecognized tax benefits, interest and penalties	$ 0	$ 0
Tax credit, investment, percent	1.32%
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carry forward subject to expiration	$ 18,100,000
Net opertaing loss carry forward not subject to expiration	$ 48,300,000
Operating loss carry forwards expiration year	2035
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry forwards expiration year	2030
2035 [Member] | Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, research and development costs	$ 2,300,000
2030 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, research and development costs	$ 1,100,000

Commitments and Contingencies-S

Commitments and Contingencies-Summary OF Future Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020 (three months remaining)	$ 1,479	$ 370
2021	1,523	1,523
2022	1,569	1,569
2023	1,616	1,616
2024	48	48
Total	$ 6,235	$ 5,126

Commitments and Contingencies -

Commitments and Contingencies -Additional Information (Detail) - USD ($) $ in Millions

Sep. 30, 2020

Jun. 30, 2020

Jul. 31, 2019

Dec. 31, 2018

Dec. 31, 2016

Dec. 31, 2015

Sep. 30, 2020

Sep. 30, 2019

Sep. 30, 2020

Sep. 30, 2019

Dec. 31, 2019

Dec. 31, 2018

May 31, 2016

Mar. 31, 2016

Operating lease terms of contract

7 years

7 years

Potential future milestone payments

$ 7.6

$ 0.8

Series A One Redeemable Convertible Preferred Stock [Member]

Percentage of net sales of company products discovered or developed prior to an IPO

1.00%

Approval Of Product [Member] | Series A One Redeemable Convertible Preferred Stock [Member]

Potential future milestone payments

$ 7.6

Revenue received on approval of product

$ 1

Ospedale San Raffaele Srl and Fondazione Telethon [Member]

Potential future milestone payments

$ 5.7

Ospedale San Raffaele Srl and Fondazione Telethon [Member] | Annual Membership Fees [Member]

Annual maintenance fee

3.9

University of Pittsburgh [Member]

Potential future milestone payments

$ 2.6

Northwestern University [Member]

Potential future milestone payments

$ 4.1

4.1

WuXi Biologics Ireland Limited [Member]

Initial payment made

$ 0.3

WuXi Biologics Ireland Limited [Member] | Clinical milestone payments [Member]

Potential future milestone payments

8

WuXi Biologics Ireland Limited [Member] | Commercial milestone payments [Member]

Potential future milestone payments

$ 27

Office Space [Member]

Rent expenses for lease

$ 0.4

$ 0.4

$ 1.1

$ 1.1

$ 1

$ 1

Lab Space [Member]

Rent expenses for lease

$ 0.4

1.1

$ 1.1

1

$ 1

Deferred Rent [Member]

Cash incentives from the landlord

$ 2.7

$ 2.7

Research and Development Expense [Member] | Ospedale San Raffaele Srl and Fondazione Telethon [Member]

Initial payment made

$ 0.1

Research and Development Expense [Member] | University of Pittsburgh [Member]

Initial payment made

0.1

Research and Development Expense [Member] | Northwestern University [Member]

Initial payment made

$ 0.1

$ 0.1

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Antidilutive Securities Excluded From Computation of Earnings Per Share (Detail) - shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	17,154,619	12,985,163	17,154,619	12,985,163	13,606,675	7,525,055
Series A-1 [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	6,328,894	6,328,894	6,328,894	6,328,894	6,328,894	6,328,894
Series B [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	8,622,625	4,590,404	8,622,625	4,590,404	5,173,569
Outstanding stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	2,109,151	1,936,493	2,109,151	1,936,493	1,991,066	970,027
Restricted stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	22,405	57,828	22,405	57,828	41,602	154,590
Common stock warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities dilute basic net loss per share	71,544	71,544	71,544	71,544	71,544	71,544

Retirement Plan - Additional In

Retirement Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Retirement plan, employer matching contribution amount	$ 0	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Thousands

Jan. 01, 2021

Dec. 29, 2020USD ($)ft²

Oct. 14, 2020USD ($)$ / sharesshares

Oct. 06, 2020$ / sharesshares

Sep. 23, 2020shares

Sep. 17, 2020USD ($)$ / sharesshares

Sep. 30, 2020USD ($)$ / sharesshares

Sep. 30, 2019USD ($)

Dec. 31, 2019USD ($)$ / sharesshares

Dec. 31, 2018$ / sharesshares

May 31, 2016

Mar. 31, 2016

Subsequent Event [Line Items]

Common stock, shares authorized

227,000,000

227,000,000

107,000,000

Common stock, par or stated value per share | $ / shares

$ 0.0001

$ 0.0001

$ 0.0001

Preferred stock, par or stated value per share | $ / shares

$ 0.0001

Proceeds from issuance of Series B preferred stock and tranche liability | $

$ 35,826

$ 47,303

$ 53,328

Lease term

7 years

7 years

Common stock reserved for future issuance

17,173,667

13,807,899

Aggregate number of outstanding shares of common stock

1.00%

2020 Plan [Member] | Restricted stock [Member]

Subsequent Event [Line Items]

Common stock reserved for future issuance

2,800,000

Share based payment award description

The number of shares reserved for issuance under the 2020 Plan will increase automatically on January 1 of each of 2021 through 2030 by the number of shares equal to the lesser of 5% of the aggregate number of outstanding shares of common stock as of the immediately preceding December 31, or a number as may be determined by the board of directors.

Aggregate number of outstanding shares of common stock

5.00%

Common Stock [Member]

Subsequent Event [Line Items]

Convertible preferred stock, shares

14,951,519

Subsequent Event [Member]

Subsequent Event [Line Items]

Gross proceeds from issuance initial public offering | $

$ 98,400

Proceeds from issuance of initial public offer | $

$ 88,300

Common stock, shares authorized

100,000,000

Preferred stock, shares authorized

10,000,000

10,000,000

Common stock, par or stated value per share | $ / shares

$ 0.0001

Preferred stock, par or stated value per share | $ / shares

$ 0.0001

$ 0.0001

Issuance of Series B preferred stock (Shares)

41,690,117

Share Price | $ / shares

$ 0.8597

Proceeds from issuance of Series B preferred stock and tranche liability | $

$ 35,800

Extended lease term

10 years

Total lease commitment | $

$ 72,000

Lease term

15 years

Pledged letter of credit | $

$ 2,900

Aggregate number of outstanding shares of common stock

1.00%

Subsequent Event [Member] | 2020 Plan [Member] | Restricted stock [Member]

Subsequent Event [Line Items]

Common stock reserved for future issuance

2,800,000

Share based payment award description

The number of shares reserved for issuance under the 2020 Plan will increase automatically on January 1 of each of 2021 through 2030 by the number of shares equal to the lesser of 5% of the aggregate number of outstanding shares of common stock as of the immediately preceding December 31, or a number as may be determined by the board of directors.

Aggregate number of outstanding shares of common stock

5.00%

Subsequent Event [Member] | POD 4 [Member]

Subsequent Event [Line Items]

Rent expense | $

100

Increase in rent expense | $

$ 200

Lease space | ft²

33,518

Subsequent Event [Member] | POD 5 [Member]

Subsequent Event [Line Items]

Rent expense | $

$ 200

Increase in rent expense | $

$ 300

Lease space | ft²

54,666

Subsequent Event [Member] | Common Stock [Member]

Subsequent Event [Line Items]

Convertible preferred stock, shares

14,951,519

Subsequent Event [Member] | IPO [Member]

Subsequent Event [Line Items]

Stock issued during period, shares, new issues

5,800,000

Share issue price | $ / shares

$ 15

Subsequent Event [Member] | Over-Allotment Option [Member]

Subsequent Event [Line Items]

Stock issued during period, shares, new issues

757,991

Share issue price | $ / shares

$ 15