Turning Point Therapeutics (TPTX) 10-K 18 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 05, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	TPTX
Entity Registrant Name	Turning Point Therapeutics, Inc.
Entity Central Index Key	0001595893
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		35,923,832
Entity File Number	001-38871
Entity Tax Identification Number	46-3826166
Entity Address, Address Line One	10628 Science Center Drive
Entity Address, Address Line Two	Ste. 200
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	926-5251
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 860.2
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission (SEC) subsequent to the date hereof pursuant to Regulation 14A in connection with the Registrant's 2020 Annual Meeting of Stockholders, are incorporated by reference into Part III of this Annual Report on Form 10-K. Such proxy statement will be filed with the SEC not later than 120 days after the conclusion of the registrant's fiscal year ended December 31, 2019.

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 48,188	$ 101,029
Marketable securities	360,963
Prepaid and other current assets	5,796	494
Total current assets	414,947	101,523
Property and equipment, net	2,689	1,000
Right-of-use lease assets	4,493
Deferred financing costs		684
Security deposits	73	73
Total assets	422,202	103,280
Current liabilities
Accounts payable	2,150	1,494
Accrued expenses and other current liabilities	3,910	2,415
Accrued compensation	6,736	1,413
Current portion of operating lease liabilities	1,236
Total current liabilities	14,032	5,322
Deferred rent		448
Operating lease liabilities, long-term	3,819
Commitments and contingencies (Note 7)
Convertible preferred stock, $0.0001 par value; zero and 65,423,901 shares authorized, issued and outstanding at December 31, 2019 and December 31, 2018, respectively; aggregate liquidation preference of $0 and $146,460 at December 31, 2019 and December 31, 2018, respectively		145,916
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 10,000,000 and zero shares authorized at December 31, 2019 and December 31, 2018, respectively; zero shares outstanding at December 31, 2019 and December 31, 2018, respectively;
Common stock, $0.0001 par value; 200,000,000 and 104,000,000 shares authorized at December 31, 2019 and December 31, 2018, respectively; 35,915,119 and 3,411,516 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	4	1
Additional paid-in capital	526,960	2,346
Accumulated other comprehensive income	271
Accumulated deficit	(122,884)	(50,753)
Total stockholders' equity (deficit)	404,351	(48,406)
Total liabilities, convertible preferred stock, and stockholders’ equity (deficit)	$ 422,202	$ 103,280

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Temporary equity, par value	$ 0.0001	$ 0.0001
Temporary equity, shares authorized	0	65,423,901
Temporary equity, shares issued	0	65,423,901
Temporary equity, shares outstanding	0	65,423,901
Temporary equity, liquidation preference	$ 0	$ 146,460
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	104,000,000
Common stock, shares issued	35,915,119	3,411,516
Common stock, shares outstanding	35,915,119	3,411,516
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares outstanding	0	0

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 57,943	$ 21,062	$ 15,241
General and administrative	19,781	4,578	1,488
Total operating expenses	77,724	25,640	16,729
Loss from operations	(77,724)	(25,640)	(16,729)
Other income, net	5,593	855	136
Net loss	(72,131)	(24,785)	(16,593)
Unrealized gain on marketable securities, net of tax	271
Comprehensive loss	$ (71,860)	$ (24,785)	$ (16,593)
Net loss per share, basic and diluted	$ (2.99)	$ (7.31)	$ (4.97)
Weighted-average common shares outstanding, basic and diluted	24,124,924	3,388,586	3,337,640

Statement of Changes in Convert

Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Convertible Preferred Stock	Series C Convertible Preferred Stock	Series D Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-in Capital	Additional Paid-in CapitalIPO	Accumulated Other Comprehensive Income	Retained Earnings (Accumulated Deficit)
Balance at Dec. 31, 2016	$ (8,658)					$ 1		$ 716			$ (9,375)
Balance, Shares at Dec. 31, 2016			19,719,133
Balance at Dec. 31, 2016			$ 21,373
Balance, Shares at Dec. 31, 2016						3,324,673
Issuance of convertible preferred stock, net of issuance costs				$ 44,788
Issuance of convertible preferred stock, net of issuance costs ,Shares				19,416,645
Option exercises	63							63
Option exercises, Shares						43,069
Stock-based compensation expense	344							344
Net loss	(16,593)										(16,593)
Balance at Dec. 31, 2017	(24,844)					$ 1		1,123			(25,968)
Balance, Shares at Dec. 31, 2017			39,135,778
Balance at Dec. 31, 2017			$ 66,161
Balance, Shares at Dec. 31, 2017						3,367,742
Issuance of convertible preferred stock, net of issuance costs					$ 79,755
Issuance of convertible preferred stock, net of issuance costs ,Shares					26,288,123
Option exercises	76							76
Option exercises, Shares						43,774
Stock-based compensation expense	1,147							1,147
Net loss	(24,785)										(24,785)
Balance at Dec. 31, 2018	$ (48,406)					$ 1		2,346			(50,753)
Balance, Shares at Dec. 31, 2018	65,423,901		65,423,901
Balance at Dec. 31, 2018	$ 145,916		$ 145,916
Balance, Shares at Dec. 31, 2018	3,411,516					3,411,516
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs		$ 364,656					$ 1		$ 364,655
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, Shares							15,137,500
Conversion of convertible preferred stock into common stock	$ 145,916		$ (145,916)			$ 2		145,914
Conversion of convertible preferred stock into common stock, Shares			(65,423,901)			16,993,194
Option exercises	$ 1,008							1,008
Option exercises, Shares	362,275					362,275
Shares issued under employee stock purchase plan	$ 331							331
Shares issued under employee stock purchase plan, Shares						10,634
Stock-based compensation expense	12,706							12,706
Net loss	(72,131)										(72,131)
Other comprehensive income	271									$ 271
Balance at Dec. 31, 2019	$ 404,351					$ 4		$ 526,960		$ 271	$ (122,884)
Balance, Shares at Dec. 31, 2019	0
Balance, Shares at Dec. 31, 2019	35,915,119					35,915,119

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (72,131)	$ (24,785)	$ (16,593)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	12,706	1,147	344
Depreciation	492	138	63
Accretion of discount on marketable securities	(1,357)
Amortization of right-of-use operating lease asset	1,087
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,302)	88	(179)
Security deposits		(35)	7
Accounts payable	903	(119)	1,286
Accrued expenses and other current liabilities	522	(945)	2,077
Accrued compensation	5,323	978	355
Net cash used in operating activities	(57,757)	(23,533)	(12,640)
Investing activities
Purchases of marketable securities	(432,173)
Sales and maturities of marketable securities	72,838
Purchases of property and equipment	(1,744)	(302)	(88)
Net cash used in investing activities	(361,079)	(302)	(88)
Financing activities
Proceeds from issuance of common stock in initial public offering, net	175,151
Proceeds from issuance of common stock in public offering, net	189,505
Proceeds from issuance of convertible preferred stock, net of issuance costs		79,755	44,788
Proceeds from issuance of common stock	1,339	76	63
Net cash provided by financing activities	365,995	79,831	44,851
Net (decrease) increase in cash and cash equivalents	(52,841)	55,996	32,123
Cash and cash equivalents at the beginning of period	101,029	45,033	12,910
Cash and cash equivalents at the end of period	48,188	101,029	45,033
Supplemental disclosure of cash flow information:
Cash paid for income taxes	1	1	$ 1
Supplemental disclosure of non-cash investing and financing information:
Purchases of property and equipment in accounts payable	490
Costs incurred in connection with the public offering included in accounts payable and accrued expenses		684
Capitalized value of tenant improvement allowance		$ 583
Operating lease liabilities arising from obtaining right-of-use assets	$ 5,554

Formation and Business of the C

Formation and Business of the Company	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company Organization Turning Point Therapeutics, Inc. (the Company) was organized on October 8, 2013, and commenced operations in 2014. The Company is a clinical-stage biopharmaceutical company designing and developing novel small molecule, targeted oncology therapies. The Company’s principal operations are in the United States and the Company operates in one segment, with its headquarters in San Diego, California. The Company’s primary activities since inception have been to build infrastructure, conduct research and development, including clinical trials, perform business and financial planning, and raise capital. Public Offerings On April 22, 2019, the Company completed an initial public offering (IPO) of its common stock. In connection with its IPO, the Company issued and sold 10,637,500 shares of its common stock at a price to the public of $18.00 per share. The net proceeds from the IPO were approximately $175.2 million after deducting underwriting discounts and commissions of $13.4 million and offering expenses of approximately $2.9 million paid by the Company. At the closing of the IPO, 65,423,901 shares of outstanding convertible preferred stock were automatically converted into 16,993,194 shares of common stock. Following the IPO, there were no shares of preferred stock outstanding. On September 10, 2019, the Company completed an underwritten public offering of its common stock, which resulted in the issuance and sale of an aggregate of 4,500,000 shares of common stock at a public offering price of $45.00 per share. $189.5 million, Reverse Stock Split On April 5, 2019, the Company effected a 1-for-3.85 reverse stock split of its common stock. The par value and the authorized number of shares of the common stock were not adjusted as a result of the reverse stock split. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented. Liquidity Management evaluates whether there are relevant conditions and events that in aggregate raise substantial doubt about the entity’s ability to continue as a going concern and to meet its obligations as they become due within one year from the date that the financial statements are issued. The Company’s activities are subject to significant risks and uncertainties, including concentration on the Company’s lead development program, which has significant competition from cancer therapies in development by other companies or already approved for sale by the U.S. Food and Drug Administration. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Drug 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent liabilities in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to the valuation of equity awards, preclinical and clinical study accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. As of December 31, 2019 and 2018, cash equivalents consisted of checking, savings, and money market balances. The Company places its cash and cash equivalents with high credit quality financial institutions. All of the Company’s cash and cash equivalent balances are maintained at three financial institutions domiciled in the United States. Marketable securities The Company classifies all marketable securities as available for sale, as the sale of such securities may be required prior to maturity. These marketable securities are carried at fair value, with unrealized gains and losses reported as accumulated other comprehensive income (loss) until realized. The cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, as well as interest and dividends, are included in interest income. Realized gains and losses from the sale of available for sale securities, if any, are determined on a specific identification basis and are also included in interest income. The Company’s marketable securities are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. At each reporting date, the Company performs an evaluation of impairment to determine if any unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and the Company’s intent and ability to hold the investment until recovery of the amortized cost basis. The Company intends, and has the ability, to hold its investments until their amortized cost basis has been recovered. Fair Value of Financial Instruments The carrying amounts of certain of the Company’s financial instruments, including cash, cash equivalents and marketable securities, prepaid expenses and other current assets, accounts payable, and accrued liabilities, approximate fair value due to the short-term nature of these items. Concentration of Credit Risk Substantially all of our cash, cash equivalents, and marketable securities are held at three financial institutions. Due to their size, we believe these financial institutions represent minimal credit risk. Cash amounts held at financial institutions are insured by the Federal Deposit Insurance Corporation (FDIC) up to $250,000. At December 31, 2019, cash and cash equivalents and marketable securities totaling $408.7 million are either not subject to FDIC insurance, or exceed the FDIC insured limit. Our cash and cash equivalents and marketable securities are invested in short term, high grade securities, and as a result, we believe represent a minimal credit risk. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful life of the assets, which ranges between three to seven years. Tenant improvements are stated at cost and depreciated over the shorter of the estimated useful life or the remaining life of the lease at the time the asset is placed into service. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when 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 respective fair value. The Company has not recognized any impairment losses during the years ended December 31, 2019, 2018 and 2017. Intellectual Property The legal and professional costs incurred by the Company to maintain its patent rights have been expensed as part of general and administrative expenses since inception. As of December 31, 2019 and 2018, the Company has determined that these expenses have not met the criteria to be capitalized. Intellectual property-related expenses for the years ended December 31, 2019, 2018 and 2017 were $0.7 million, $0.5 million and $0.2 million, respectively. General and Administrative Expenses General and administrative expenses consist primarily of salaries and related costs, including stock-based compensation, for personnel in executive, finance and administrative functions. General and administrative expenses also include direct and allocated facility-related costs as well as professional fees for legal, consulting, accounting and audit services. Research and Development Expenses Research and development costs are expensed as incurred. These costs consist primarily of salaries and other personnel-related expenses, including stock-based compensation; facility-related expenses; depreciation of facilities and equipment; laboratory consumables; and services performed by clinical research organizations, research institutions, and other outside service providers. The Company recorded the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced and include these costs in accrued expenses and other current liabilities accrued expenses and other current liabilities Income Taxes Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities using enacted tax rates which will be in effect when the differences reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax asset will be realized. The Company follows the provisions of the Income Taxes Topic of the Financial Accounting Standards Board (FASB) Accounting Standards Codification that defines a recognition threshold and measurement attributes for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Under the Income Taxes Topic, the impact of an uncertain income tax position on the income tax return must be recognized at the largest amount that is more-likely-than-not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Stock-Based Compensation For purposes of calculating stock-based compensation, the Company estimates the fair value of stock options issued using a Black-Scholes option-pricing model. The determination of the fair value of stock-based payment awards utilizing the Black-Scholes model is affected by the Company’s stock price and a number of assumptions, including expected volatility, expected life, risk-free interest rate and expected dividends. Expected Term —The Company uses the “simplified method” for estimating the expected term of employee options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option (generally 10 years). Expected Volatility —Due to the Company’s limited operating history and a lack of company specific historical and implied volatility data, the Company estimates expected volatility based on the historical volatility of a group of similar companies that are publicly traded. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. Risk-Free Interest Rate —The risk-free rate assumption is based on the U.S. Treasury instruments with maturities similar to the expected term of the stock options. Expected Dividend —The Company has not issued any dividends and does not expect to issue dividends over the life of the options. As a result, the Company has estimated the dividend yield to be zero. The estimated fair value of stock options granted to employees and non-employee service providers are expensed over the requisite service period (generally the vesting term) on a straight-line basis , net of actual forfeitures during the period Net Loss Per Share The Company computes basic loss per share by dividing the net loss available to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss assumes the conversion, exercise or issuance of all potential common stock equivalents, unless the effect of inclusion would be anti-dilutive. For purposes of this calculation, common stock equivalents include the Company’s stock options and convertible preferred stock, which is convertible into shares of the Company’s common stock. No shares related to the convertible preferred stock were included in the diluted net loss calculation for the years ended December 31, 2019, 2018 or 2017 because the inclusion of such shares would have had an anti-dilutive effect. The shares to be issued upon exercise of certain outstanding stock options were also excluded from the diluted net loss calculation for the years ended December 31, 2019, 2018 and 2017 because such shares are anti-dilutive. Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2019 2018 2017 Convertible preferred stock (as converted) – 16,993,194 10,165,120 Common stock options 5,254,269 3,597,638 584,019 Total 5,254,269 20,590,832 10,749,139 Recent Accounting Pronouncements In June 2016, the FASB issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement Recently Adopted Accounting Standards Updates In February 2016, the FASB issued ASU No. 2016-02, “ Leases The Company currently has one operating lease for office and laboratory spaces in San Diego, California. The operating lease was impacted by the new accounting standard and resulted in the present values of the future lease payments being presented as a right-to-use asset, with a corresponding lease liability at the date of adoption. The financial impact from the adoption of this guidance is discussed in Note 7. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740),

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities	3. Marketable Securities T he Company invests its excess cash in marketable securities, including debt instruments of financial institutions, corporations with investment grade credit ratings, commercial paper and government agencies. At December 31, 2019, marketable securities consisted of the following (in thousands): Unrealized Maturity in Years Amortized Cost Gains Losses Fair Value U.S. government agency securities 2 years or less $ 90,596 $ 42 $ (20 ) $ 90,618 Corporate debt securities 2 years or less 173,595 178 (21 ) 173,752 Commercial paper Less than 1 96,501 92 - 96,593 Total marketable securities $ 360,692 $ 312 $ (41 ) $ 360,963 The Company’s marketable securities are presented as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date. This presentation reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. ross realized gains and losses on available for sale securities were immaterial during the year ended December 31, 2019. No .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Fair value should maximize the use of observable inputs and minimize the use of unobservable inputs. The Company determines the fair value of financial assets and liabilities using three levels of inputs as follows: Level 1—Inputs which include quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted market prices included in Level 1) that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life. Level 3—Unobservable inputs for assets or liabilities and include little or no market activity. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company’s financial assets subject to fair value measurements on a recurring basis and the level of inputs used for such measurements were as follows (in thousands): Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Money market funds and corporate securities included in cash and cash equivalents $ 45,085 $ - $ - $ 45,085 U.S. government agency securities - 90,618 - 90,618 Corporate debt securities - 173,752 - 173,752 Commercial paper - 96,593 - 96,593 Total marketable securities $ 45,085 $ 360,963 $ - $ 406,048 Fair Value Measurements at December 31, 2018 Using: Level 1 Level 2 Level 3 Total Money market funds included in cash and cash equivalents $ 98,268 $ - $ - $ 98,268

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, December 31, 2019 2018 Laboratory equipment $ 885 $ 388 Computer equipment and software 910 138 Tenant improvements 1,108 679 Furniture and fixtures 357 66 Property and equipment 3,260 1,271 Less: accumulated depreciation (571 ) (271 ) Property and equipment, net $ 2,689 $ 1,000 Depreciation expense for the years ended December 31, 2019, 2018 and 2017 was $0.5 million, $0.1 million and $0.1 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, 2019 2018 Accrued research and development expenses $ 3,414 $ 1,677 Accrued general and administrative expenses 451 548 Other current liabilities 45 190 Total $ 3,910 $ 2,415

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Operating Leases On January 1, 2019, in conjunction with the adoption of the guidance in ASU 2016-02 - “ Leases”, In June 2019, the Company amended the terms of its existing facility lease in conjunction with entering into a lease for additional office and laboratory space and agreed to surrender a portion of its current laboratory and office space and to extend the lease term for its remaining laboratory and office space to June 30, 2023. The execution of the new lease and the amendment to the Company’s existing facility lease were accounted for as a single contract for accounting purposes, as the counterparty to both contracts is the Company’s existing landlord and both agreements were negotiated contemporaneously as a whole to achieve the same commercial objective. In June 2019, the Company accounted for the partial surrender of office and laboratory space as a reduction to its existing right-of-use asset and liability totaling $0.6 million, and $0.9 million, respectively. The difference between these amounts was recorded as a deferred gain of $0.3 million. The deferred gain was recorded as an offset to the right of use asset recorded by the Company on July 1, 2019. In June 2019, and in connection with the extension of the lease term of the Company’s previously existing office and laboratory space, the Company recognized an incremental increase of $0.5 million to its existing right of use asset and lease liability. The adjustment was computed assuming a lease term ending in June 2023 and an estimated incremental borrowing rate of 8.5%. This right-of-use asset was recorded net of $0.3 million associated with the lease extension, which represents the Company’s net unamortized capitalized tenant improvement allowance and deferred rent. The new lease commenced in July 2019 and the lease expiration date is June 30, 2023. In addition to base rental payments under this lease, which escalate over the term of the lease, the Company will also be responsible for the payment of its share of the estimated annual operating expenses, property tax expenses, and utilities costs related to this lease of additional space. The lease also contains an option to extend the lease term on all leased space for one additional five-year term. As of July 1, 2019, the Company was not reasonably certain that it would exercise the extension option, and as such, did not include this option in the determination of the total lease term for accounting purposes. The right-of-use asset and corresponding lease liability was estimated assuming the remaining lease term of 48 months at July 1, 2019, and an estimated discount rate of 8.5%, which was the Company’s incremental borrowing rate at the date of the lease commencement. The Company recorded a lease liability of $4.0 million and a right-of-use asset of $3.7 million, which is net of $0.3 million of the Company’s deferred gain from the office and laboratory space surrendered in June 2019. Future minimum payments under the amended lease as of December 31, 2019 are as follows (in thousands) 2020 1,618 2021 1,668 2022 1,718 2023 872 Total future minimum lease payments 5,876 Less: amounts representing interest (821 ) Total lease liability $ 5,055 Remaining lease term 3.5 years Rent expense for the years ended December 31, 2019, 2018 and 2017 was approximately $1.1 million, $0.5 million and million and $0.4 million, respectively elated to its operating lease agreement of $1.2 million, $0.5 million and $0.4 million for the years ended December 31, 2019, 2018 and 2017, respectively

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Stock Option Plan T he Company’s 2019 Equity Incentive Plan as amended (the Plan), provides for the grant of stock options, restricted stock and other equity awards of the Company’s common stock to employees, officers, consultants, and directors. As of December 31, 2019, the Plan had a maximum of 2,633,874 total shares available for issuance. Options expire within a period of not more than ten years from the date of grant. Initial option grants to employees typically vest 25% after one year and monthly thereafter over a three-year period and expire between one and three months after employee termination. Subsequent option grants to employees and grants to non-employees typically vest monthly over a four-year period. The majority of options outstanding at December 31, 2019, had vesting periods of four years. The weighted-average grant-date fair value of options granted to employees was $21.66, $6.23 and $2.08 for the years ended December 31, 2019, 2018 and 2017, respectively. As of December 31, 2019, unrecognized compensation expense related to unvested options was $54.4 million and is expected to be recognized over a weighted average term of 2.92 years. The following summarizes option activity for the year ended December 31, 2019: Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances as of December 31, 2018 3,597,638 $ 4.40 9.5 $ 15,056 Options granted 2,362,266 $ 27.22 Options exercised (362,275 ) $ 2.78 Options forfeited (343,360 ) $ 7.15 Balances as of December 31, 2019 5,254,269 $ 14.59 9.0 $ 250,611 Options vested and exercisable as of December 31, 2019 1,060,942 $ 4.60 8.5 $ 61,203 The fair values of the employee stock options granted during 2019, 2018 and 2017 was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2019 2018 2017 Risk-free interest rate 2.13 % 2.61 - 3.10 % 1.94 - 2.22 % Volatility 79.8 % 80.4 - 82.5 % 91.3 % Expected term (in years) 6.05 5.77 - 6.08 5.00 - 6.08 Dividend yield - - - 2019 Employee Stock Purchase Plan In April 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Employee Stock Purchase Plan (the “ESPP”). The ESPP became effective immediately prior to the date of the underwriting agreement related to the IPO. The ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to 15% of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the ESPP. The price of common stock purchased under the ESPP is equal to 85 percent of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant date of purchase. Each offering period is 24 months, with new offering periods commencing every six months on the dates of June 11 and December 11 of each year. Each offering period consists of four (4) six month purchase periods (each a “Purchase Period”) during which payroll deductions of the participants are accumulated under the ESPP. The last business day of each Purchase Period is referred to as the “Purchase Date.” Purchase Dates are every six months on the dates of June 10 and December 10 of each year. As of December 31, 2019, unrecognized compensation expense related to the ESPP was $0.9 million. The assumptions used for the year ended December 31, 2019 and the resulting estimates of weighted-average fair value per share for stock purchased under the ESPP during 2019 were as follows : Year Ended December 31, 2019 Risk-free interest rate 1.55 - 2.13% Volatility 70.6 - 76.2% Expected term (in years) 0.50 - 2.00 Dividend yield - Stock-based compensation expense resulting from grants under the Company’s stock option plan and employee stock purchase plan is reflected in the statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 6,075 $ 556 $ 184 General and administrative 6,631 591 160 Total stock-based compensation $ 12,706 $ 1,147 $ 344 Common Stock Reserved for Future Issuance Common stock reserved for future issuance consists of the following: December 31, 2019 2018 Conversion of preferred stock outstanding – 16,993,194 Common stock options outstanding 5,254,269 3,597,638 Options to purchase common stock available for issuance under equity incentive plan 2,633,874 1,816,266 Shares available for purchase under employee stock purchase plan 278,304 - Total 8,166,447 22,407,098

Defined Contribution Benefit Pl

Defined Contribution Benefit Plan	12 Months Ended
	Dec. 31, 2019
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Defined Contribution Benefit Plan	9. Defined Contribution Benefit Plan The Company sponsors a 401(k) retirement plan, in which substantially all of its full-time employees are eligible to participate. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. The Company has recorded as expense $0.5 million, $0.2 million and $21,000 in matching contributions for the years ended December 31, 2019, 2018 and 2017, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes No provision for federal or state income taxes has been recorded for the years ended December 31, 2019, 2018 and 2017 other than the $800 annual tax for C corporations paid to the state of California. A reconciliation of the federal statutory income tax rate and the Company’s effective income tax rate is as follows: Year Ended December 31, 2019 2018 2017 Tax computed at federal statutory rate 21.0 % 21.0 % 34.0 % Permanent items and other — (2.4 ) (9.4 ) Stock based compensation 1.6 (0.8 ) (0.3 ) Research and development tax credits 1.6 1.1 (1.2 ) Orphan drug tax credit 6.8 6.5 13.1 Tax Cuts and Jobs Act — — (16.4 ) Valuation allowance (31.0 ) (25.4 ) (19.8 ) Effective income tax rate — % — % — % Deferred tax assets and liabilities consist of the following (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 22,226 $ 8,474 Research and development credits 1,521 353 Orphan drug credit 8,657 3,781 Accrued liabilities 1,073 287 Right of use asset 1,062 — Stock based compensation 1,909 — Other, net — 115 Total deferred tax assets 36,448 13,010 Deferred tax liabilities Fixed assets (154 ) (7 ) Lease liabilities (944 ) — (1,098 ) (7 ) Total 35,350 13,003 Less: valuation allowance (35,350 ) (13,003 ) Net deferred tax assets $ — $ — The valuation allowance increased by $22.3 million during the year ended December 31, 2019. Due to the uncertainties surrounding the realization of deferred tax assets, the Company has provided a full valuation allowance and, therefore, no benefit has been recognized for the net operating loss carryforwards and other deferred tax assets. At December 31, 2019, the Company has federal and state net operating loss carryforwards of approximately $105.8 million and $111.6 million, respectively. Portions of the The Company files income tax returns in the United States federal jurisdiction and in California, and the tax returns filed for the years 2014 through 2018 have not been examined and the applicable statutes of limitation have not expired with respect to those returns. Because of net operating loss and research credit carryforwards, substantially all of the Company’s tax years remain open to examination. Total unrecognized income tax benefits related to California net operating loss carryforwards, federal and California research and development and federal Orphan drug tax credit carryforwards were approximately $14.8 million at December 31, 2019. The Company’s policy is to include interest and penalties related to unrecognized tax benefits within the Company’s provision for income taxes. As of December 31, 2019, the Company has no accrual for interest and penalties related to unrecognized tax benefits. There are no unrecognized tax benefits that, if recognized, would impact the Company’s effective tax rate due to valuation allowances. The Company does not expect any unrecognized tax benefits to be recognized within the next 12 months. Pursuant to Sections 382 and 383, use of the Company’s net operating loss and credit carryforwards may be limited if a cumulative change in ownership of more than 50% (by value) occurs within a three-year period. The Company has not analysis net operating loss and research and development carryforwards , and these financial statements do not contain any adjustment relating to such potential limitations. However, if the Company experienced an ownership change that resulted in an limitation there would be no material impact to the financial statements. The Company recognizes a tax benefit from an uncertain tax position when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Income tax positions must meet a more likely than not recognition at the effective date to be recognized. Approximately $12.6 million of the unrecognized tax benefits would reduce the Company’s annual effective tax rate, if recognized, subject to the valuation allowance. It is not anticipated that there will be significant change in the unrecognized tax benefits over the next 12 months. A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in thousands): December 31, 2019 2018 2017 Beginning balance $ 7,488 $ 4,733 $ 954 Additions (reductions) for tax positions taken in prior years 41 (118 ) (34 ) Additions for tax positions taken in current year 7,287 2,873 3,813 Ending balance $ 14,816 $ 7,488 $ 4,733 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 the United States Internal Revenue Service and the taxing authorities in state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years from inception in 2013 and onwards are subject to examination by the federal and state tax authorities due to the carryforward of unutilized net operating losses and research and development credits. The Company’s practice is to recognize interest and penalties related to income tax matters in income tax expense. The Company has not recognized interest or penalties since inception.

Selected Quarterly Financial In

Selected Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	Note 11—Selected Quarterly Financial Information (Unaudited) The following is a summary of the quarterly results of the Company for the years ended December 31, 2019 and 2018 ( ): Year Ended December 31, 2019 12/31/2019 9/30/2019 6/30/2019 3/31/2019 Loss from operations (23,065 ) (22,140 ) (18,454 ) (14,065 ) Net loss (20,959 ) (20,483 ) (17,142 ) (13,547 ) Net loss per share, basic and diluted $ (0.58 ) $ (0.63 ) $ (0.70 ) $ (3.97 ) Weighted-average common shares outstanding, basic and diluted 35,851,252 32,312,814 24,479,767 3,413,760 Year Ended December 31, 2018 12/31/2018 9/30/2018 6/30/2018 3/31/2018 Loss from operations (9,479 ) (6,129 ) (5,172 ) (4,860 ) Net loss (9,018 ) (5,997 ) (5,037 ) (4,733 ) Net income per share, basic and diluted $ (2.64 ) $ (1.77 ) $ (1.49 ) $ (1.41 ) Weighted-average common shares outstanding, basic and diluted 3,409,874 3,394,423 3,380,899 3,368,608

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Note 12— Subsequent Events In January 2020, the Company entered into a Transition Separation and Consulting Agreement with the Company’s Chief Scientific Officer, Dr. Jingrong Jean Cui. In connection with this agreement, Dr. Cui’s resigned from her position as Chief Scientific Officer effective January 31, 2020. In accordance with the terms of the agreement with Dr. Cui, the Company will record an expense in the amount of $1.2 million during fiscal year 2020 representing the cash severance that will be paid to Dr. Cui during 2020. In addition, the Company anticipates recording non-cash stock-based compensation expense in fiscal year 2020 related to the modification of Dr. Cui’s outstanding stock option grants.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent liabilities in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to the valuation of equity awards, preclinical and clinical study accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. As of December 31, 2019 and 2018, cash equivalents consisted of checking, savings, and money market balances. The Company places its cash and cash equivalents with high credit quality financial institutions. All of the Company’s cash and cash equivalent balances are maintained at three financial institutions domiciled in the United States.
Marketable Securities	Marketable securities The Company classifies all marketable securities as available for sale, as the sale of such securities may be required prior to maturity. These marketable securities are carried at fair value, with unrealized gains and losses reported as accumulated other comprehensive income (loss) until realized. The cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, as well as interest and dividends, are included in interest income. Realized gains and losses from the sale of available for sale securities, if any, are determined on a specific identification basis and are also included in interest income. The Company’s marketable securities are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. At each reporting date, the Company performs an evaluation of impairment to determine if any unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and the Company’s intent and ability to hold the investment until recovery of the amortized cost basis. The Company intends, and has the ability, to hold its investments until their amortized cost basis has been recovered.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of certain of the Company’s financial instruments, including cash, cash equivalents and marketable securities, prepaid expenses and other current assets, accounts payable, and accrued liabilities, approximate fair value due to the short-term nature of these items.
Concentration of Credit Risk	Concentration of Credit Risk Substantially all of our cash, cash equivalents, and marketable securities are held at three financial institutions. Due to their size, we believe these financial institutions represent minimal credit risk. Cash amounts held at financial institutions are insured by the Federal Deposit Insurance Corporation (FDIC) up to $250,000. At December 31, 2019, cash and cash equivalents and marketable securities totaling $408.7 million are either not subject to FDIC insurance, or exceed the FDIC insured limit. Our cash and cash equivalents and marketable securities are invested in short term, high grade securities, and as a result, we believe represent a minimal credit risk.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful life of the assets, which ranges between three to seven years. Tenant improvements are stated at cost and depreciated over the shorter of the estimated useful life or the remaining life of the lease at the time the asset is placed into service.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when 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 respective fair value. The Company has not recognized any impairment losses during the years ended December 31, 2019, 2018 and 2017.
Intellectual Property	Intellectual Property The legal and professional costs incurred by the Company to maintain its patent rights have been expensed as part of general and administrative expenses since inception. As of December 31, 2019 and 2018, the Company has determined that these expenses have not met the criteria to be capitalized. Intellectual property-related expenses for the years ended December 31, 2019, 2018 and 2017 were $0.7 million, $0.5 million and $0.2 million, respectively.
General and Administrative Expenses	General and Administrative Expenses General and administrative expenses consist primarily of salaries and related costs, including stock-based compensation, for personnel in executive, finance and administrative functions. General and administrative expenses also include direct and allocated facility-related costs as well as professional fees for legal, consulting, accounting and audit services.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. These costs consist primarily of salaries and other personnel-related expenses, including stock-based compensation; facility-related expenses; depreciation of facilities and equipment; laboratory consumables; and services performed by clinical research organizations, research institutions, and other outside service providers. The Company recorded the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced and include these costs in accrued expenses and other current liabilities accrued expenses and other current liabilities
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities using enacted tax rates which will be in effect when the differences reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax asset will be realized. The Company follows the provisions of the Income Taxes Topic of the Financial Accounting Standards Board (FASB) Accounting Standards Codification that defines a recognition threshold and measurement attributes for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. Under the Income Taxes Topic, the impact of an uncertain income tax position on the income tax return must be recognized at the largest amount that is more-likely-than-not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained.
Stock-Based Compensation	Stock-Based Compensation For purposes of calculating stock-based compensation, the Company estimates the fair value of stock options issued using a Black-Scholes option-pricing model. The determination of the fair value of stock-based payment awards utilizing the Black-Scholes model is affected by the Company’s stock price and a number of assumptions, including expected volatility, expected life, risk-free interest rate and expected dividends. Expected Term —The Company uses the “simplified method” for estimating the expected term of employee options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option (generally 10 years). Expected Volatility —Due to the Company’s limited operating history and a lack of company specific historical and implied volatility data, the Company estimates expected volatility based on the historical volatility of a group of similar companies that are publicly traded. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. Risk-Free Interest Rate —The risk-free rate assumption is based on the U.S. Treasury instruments with maturities similar to the expected term of the stock options. Expected Dividend —The Company has not issued any dividends and does not expect to issue dividends over the life of the options. As a result, the Company has estimated the dividend yield to be zero. The estimated fair value of stock options granted to employees and non-employee service providers are expensed over the requisite service period (generally the vesting term) on a straight-line basis , net of actual forfeitures during the period
Net Loss Per Share	Net Loss Per Share The Company computes basic loss per share by dividing the net loss available to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss assumes the conversion, exercise or issuance of all potential common stock equivalents, unless the effect of inclusion would be anti-dilutive. For purposes of this calculation, common stock equivalents include the Company’s stock options and convertible preferred stock, which is convertible into shares of the Company’s common stock. No shares related to the convertible preferred stock were included in the diluted net loss calculation for the years ended December 31, 2019, 2018 or 2017 because the inclusion of such shares would have had an anti-dilutive effect. The shares to be issued upon exercise of certain outstanding stock options were also excluded from the diluted net loss calculation for the years ended December 31, 2019, 2018 and 2017 because such shares are anti-dilutive. Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2019 2018 2017 Convertible preferred stock (as converted) – 16,993,194 10,165,120 Common stock options 5,254,269 3,597,638 584,019 Total 5,254,269 20,590,832 10,749,139
Recent Accounting Pronouncements and Recently Adopted Accounting Standards Updates	Recent Accounting Pronouncements In June 2016, the FASB issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement Recently Adopted Accounting Standards Updates In February 2016, the FASB issued ASU No. 2016-02, “ Leases The Company currently has one operating lease for office and laboratory spaces in San Diego, California. The operating lease was impacted by the new accounting standard and resulted in the present values of the future lease payments being presented as a right-to-use asset, with a corresponding lease liability at the date of adoption. The financial impact from the adoption of this guidance is discussed in Note 7. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740),

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Outstanding Anti-dilutive Securities Not Included in the Diluted Net Loss Per Share	Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2019 2018 2017 Convertible preferred stock (as converted) – 16,993,194 10,165,120 Common stock options 5,254,269 3,597,638 584,019 Total 5,254,269 20,590,832 10,749,139

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Marketable Securities	At December 31, 2019, marketable securities consisted of the following (in thousands): Unrealized Maturity in Years Amortized Cost Gains Losses Fair Value U.S. government agency securities 2 years or less $ 90,596 $ 42 $ (20 ) $ 90,618 Corporate debt securities 2 years or less 173,595 178 (21 ) 173,752 Commercial paper Less than 1 96,501 92 - 96,593 Total marketable securities $ 360,692 $ 312 $ (41 ) $ 360,963

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Financial Assets Subject to Fair Value Measurements on a Recurring Basis and the Level of Inputs	The Company’s financial assets subject to fair value measurements on a recurring basis and the level of inputs used for such measurements were as follows (in thousands): Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Money market funds and corporate securities included in cash and cash equivalents $ 45,085 $ - $ - $ 45,085 U.S. government agency securities - 90,618 - 90,618 Corporate debt securities - 173,752 - 173,752 Commercial paper - 96,593 - 96,593 Total marketable securities $ 45,085 $ 360,963 $ - $ 406,048 Fair Value Measurements at December 31, 2018 Using: Level 1 Level 2 Level 3 Total Money market funds included in cash and cash equivalents $ 98,268 $ - $ - $ 98,268

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): December 31, December 31, 2019 2018 Laboratory equipment $ 885 $ 388 Computer equipment and software 910 138 Tenant improvements 1,108 679 Furniture and fixtures 357 66 Property and equipment 3,260 1,271 Less: accumulated depreciation (571 ) (271 ) Property and equipment, net $ 2,689 $ 1,000

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, 2019 2018 Accrued research and development expenses $ 3,414 $ 1,677 Accrued general and administrative expenses 451 548 Other current liabilities 45 190 Total $ 3,910 $ 2,415

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Summary of Operating Leases Future Minimum Payments	Future minimum payments under the amended lease as of December 31, 2019 are as follows (in thousands) 2020 1,618 2021 1,668 2022 1,718 2023 872 Total future minimum lease payments 5,876 Less: amounts representing interest (821 ) Total lease liability $ 5,055 Remaining lease term 3.5 years

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Option Activity	The following summarizes option activity for the year ended December 31, 2019: Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balances as of December 31, 2018 3,597,638 $ 4.40 9.5 $ 15,056 Options granted 2,362,266 $ 27.22 Options exercised (362,275 ) $ 2.78 Options forfeited (343,360 ) $ 7.15 Balances as of December 31, 2019 5,254,269 $ 14.59 9.0 $ 250,611 Options vested and exercisable as of December 31, 2019 1,060,942 $ 4.60 8.5 $ 61,203
Schedule of Fair Values of Employee Stock Options Granted	The fair values of the employee stock options granted during 2019, 2018 and 2017 was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2019 2018 2017 Risk-free interest rate 2.13 % 2.61 - 3.10 % 1.94 - 2.22 % Volatility 79.8 % 80.4 - 82.5 % 91.3 % Expected term (in years) 6.05 5.77 - 6.08 5.00 - 6.08 Dividend yield - - - The assumptions used for the year ended December 31, 2019 and the resulting estimates of weighted-average fair value per share for stock purchased under the ESPP during 2019 were as follows : Year Ended December 31, 2019 Risk-free interest rate 1.55 - 2.13% Volatility 70.6 - 76.2% Expected term (in years) 0.50 - 2.00 Dividend yield -
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]	Stock-based compensation expense resulting from grants under the Company’s stock option plan and employee stock purchase plan is reflected in the statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 6,075 $ 556 $ 184 General and administrative 6,631 591 160 Total stock-based compensation $ 12,706 $ 1,147 $ 344
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance consists of the following: December 31, 2019 2018 Conversion of preferred stock outstanding – 16,993,194 Common stock options outstanding 5,254,269 3,597,638 Options to purchase common stock available for issuance under equity incentive plan 2,633,874 1,816,266 Shares available for purchase under employee stock purchase plan 278,304 - Total 8,166,447 22,407,098

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate	A reconciliation of the federal statutory income tax rate and the Company’s effective income tax rate is as follows: Year Ended December 31, 2019 2018 2017 Tax computed at federal statutory rate 21.0 % 21.0 % 34.0 % Permanent items and other — (2.4 ) (9.4 ) Stock based compensation 1.6 (0.8 ) (0.3 ) Research and development tax credits 1.6 1.1 (1.2 ) Orphan drug tax credit 6.8 6.5 13.1 Tax Cuts and Jobs Act — — (16.4 ) Valuation allowance (31.0 ) (25.4 ) (19.8 ) Effective income tax rate — % — % — %
Summary of Deferred Tax Assets and Liabilities	Deferred tax assets and liabilities consist of the following (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 22,226 $ 8,474 Research and development credits 1,521 353 Orphan drug credit 8,657 3,781 Accrued liabilities 1,073 287 Right of use asset 1,062 — Stock based compensation 1,909 — Other, net — 115 Total deferred tax assets 36,448 13,010 Deferred tax liabilities Fixed assets (154 ) (7 ) Lease liabilities (944 ) — (1,098 ) (7 ) Total 35,350 13,003 Less: valuation allowance (35,350 ) (13,003 ) Net deferred tax assets $ — $ —
Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in thousands): December 31, 2019 2018 2017 Beginning balance $ 7,488 $ 4,733 $ 954 Additions (reductions) for tax positions taken in prior years 41 (118 ) (34 ) Additions for tax positions taken in current year 7,287 2,873 3,813 Ending balance $ 14,816 $ 7,488 $ 4,733

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results	The following is a summary of the quarterly results of the Company for the years ended December 31, 2019 and 2018 ( ): Year Ended December 31, 2019 12/31/2019 9/30/2019 6/30/2019 3/31/2019 Loss from operations (23,065 ) (22,140 ) (18,454 ) (14,065 ) Net loss (20,959 ) (20,483 ) (17,142 ) (13,547 ) Net loss per share, basic and diluted $ (0.58 ) $ (0.63 ) $ (0.70 ) $ (3.97 ) Weighted-average common shares outstanding, basic and diluted 35,851,252 32,312,814 24,479,767 3,413,760 Year Ended December 31, 2018 12/31/2018 9/30/2018 6/30/2018 3/31/2018 Loss from operations (9,479 ) (6,129 ) (5,172 ) (4,860 ) Net loss (9,018 ) (5,997 ) (5,037 ) (4,733 ) Net income per share, basic and diluted $ (2.64 ) $ (1.77 ) $ (1.49 ) $ (1.41 ) Weighted-average common shares outstanding, basic and diluted 3,409,874 3,394,423 3,380,899 3,368,608

Formation and Business of the_2

Formation and Business of the Company - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 10, 2019USD ($)$ / sharesshares	Apr. 22, 2019USD ($)$ / sharesshares	Apr. 05, 2019	Oct. 08, 2013Segment	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)
Basis Of Presentation [Line Items]
Number of operating segments | Segment				1
Proceeds from issuance of shares, net | $					$ 1,339	$ 76	$ 63
Convertible preferred stock, outstanding | shares					0	65,423,901
Preferred stock, shares outstanding | shares					0	0
Reverse stock split ratio			0.259
IPO
Basis Of Presentation [Line Items]
Number of shares issued | shares		10,637,500
Shares issued, price per share | $ / shares		$ 18
Proceeds from issuance of shares, net | $		$ 175,200
Underwriting discounts and commissions | $		13,400
Offering expenses | $		$ 2,900
Convertible preferred stock, outstanding | shares		65,423,901
Number of convertible preferred stock converted into common stock | shares		16,993,194
Preferred stock, shares outstanding | shares		0
Underwritten Public Offering
Basis Of Presentation [Line Items]
Number of shares issued | shares	4,500,000
Shares issued, price per share | $ / shares	$ 45
Proceeds from issuance of shares, net | $	$ 189,500
Underwriting discounts and commissions | $	12,200
Offering expenses | $	$ 800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019USD ($)OperatingLeaseshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares
Significant Accounting Policies [Line Items]
Exceed of federal deposits insurance limit	$ 408,700,000
Impairment of long-lived assets	0	$ 0	$ 0
Intellectual property related expenses	$ 700,000	$ 500,000	$ 200,000
Stock options expected contractual term	6 years 18 days
Expected dividend yield rate	0.00%
Number of shares related to convertible preferred stock included in diluted net loss calculation | shares	0	0	0
Number of operating lease | OperatingLease	1
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life	3 years
Stock options expected contractual term		5 years 9 months 7 days	5 years
Maximum
Significant Accounting Policies [Line Items]
Cash FDIC insured amount	$ 250,000
Estimated useful life	7 years
Stock options expected contractual term		6 years 29 days	6 years 29 days
Arithmetic Average
Significant Accounting Policies [Line Items]
Stock options expected contractual term	10 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Outstanding Anti-dilutive Securities Not Included in the Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share	5,254,269	20,590,832	10,749,139
Convertible Preferred Stock as Converted
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share		16,993,194	10,165,120
Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share	5,254,269	3,597,638	584,019

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Marketable Securities [Line Items]
Amortized Cost	$ 360,692
Unrealized Gains	312
Unrealized Losses	(41)
Fair Value	$ 360,963
U.S. Government Agency Securities
Marketable Securities [Line Items]
Maturity in Years	2 years or less
Amortized Cost	$ 90,596
Unrealized Gains	42
Unrealized Losses	(20)
Fair Value	$ 90,618
Corporate Debt Securities
Marketable Securities [Line Items]
Maturity in Years	2 years or less
Amortized Cost	$ 173,595
Unrealized Gains	178
Unrealized Losses	(21)
Fair Value	$ 173,752
Commercial Paper
Marketable Securities [Line Items]
Maturity in Years	Less than 1
Amortized Cost	$ 96,501
Unrealized Gains	92
Fair Value	$ 96,593

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Marketable securities		$ 0
Unrealized losses recognized	$ 0
Maximum period in which investment is in gross unrealized loss	12 months
Other-than-temporary losses, marketable securities	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets Subject to Fair Value Measurements on a Recurring Basis and the Level of Inputs (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	$ 406,048
Money Market Funds And Corporate Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	45,085
U.S Government Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	90,618
Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	173,752
Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	96,593
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities		$ 98,268
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	45,085
Level 1 | Money Market Funds And Corporate Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	45,085
Level 1 | Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities		$ 98,268
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	360,963
Level 2 | U.S Government Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	90,618
Level 2 | Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	173,752
Level 2 | Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	$ 96,593

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,260	$ 1,271
Less: accumulated depreciation	(571)	(271)
Property and equipment, net	2,689	1,000
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	885	388
Computer Equipment And Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	910	138
Tenant Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,108	679
Furniture And Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 357	$ 66

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation	$ 492	$ 138	$ 63

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 3,414	$ 1,677
Accrued general and administrative expenses	451	548
Other current liabilities	45	190
Total	$ 3,910	$ 2,415

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	Jul. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Commitment and Contingencies [Line Items]
Operating lease, right-of-use asset	$ 3,700	$ 4,493			$ 1,700
Operating lease right-to-use liability	$ 4,000	$ 5,055			$ 2,300
Operating lease, remaining lease term	48 months	3 years 6 months			36 months
Operating lease, estimated discount rate	8.50%				8.50%
Previously capitalized tenant improvement allowance and deferred rent					$ 600
Lease expiration date		Jun. 30, 2023
Operating lease, option to extend description		The lease also contains an option to extend the lease term on all leased space for one additional five-year term.
Rent expense		$ 1,100	$ 500	$ 400
Operating lease, cash payments		1,200	$ 500	$ 400
Lease Maturity Extension
Commitment and Contingencies [Line Items]
Operating lease, right-of-use asset		500
Operating lease right-to-use liability		$ 500
Operating lease, estimated discount rate		8.50%
Write-off of right of use assets		$ 600
Write-off of lease liabilities		900
Deferred gain	$ 300	$ 300
Lessee, operating lease, existence of option to extend [true false]		true
Lease Maturity Extension | Unamortized Capitalized Tenant Improvement Allowance And Deferred Rent
Commitment and Contingencies [Line Items]
Operating lease, right-of-use asset		$ 300

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Operating Leases Future Minimum Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jul. 01, 2019	Jan. 01, 2019
Commitments And Contingencies Disclosure [Abstract]
2020	$ 1,618
2021	1,668
2022	1,718
2023	872
Total future minimum lease payments	5,876
Less: amounts representing interest	(821)
Operating lease right-to-use liability	$ 5,055	$ 4,000	$ 2,300
Remaining lease term	3 years 6 months	48 months	36 months

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance	2,633,874	1,816,266
Weighted-average grant-date fair value of options granted to employees	$ 21.66	$ 6.23	$ 2.08
Unrecognized compensation expense related to unvested options	$ 54.4
Unrecognized compensation cost related to unvested options to be recognized over weighted average period	2 years 11 months 1 day
Common stock initially reserved for ESPP	8,166,447	22,407,098
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance	2,633,874
2019 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period	10 years
2019 Equity Incentive Plan | Maximum | After 2nd year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period	3 months
2019 Equity Incentive Plan | Minimum | After 2nd year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period	1 month
2019 Equity Incentive Plan | Employees | After one year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights	Initial option grants to employees typically vest 25% after one year and monthly thereafter over a three-year period and expire between one and three months after employee termination.
Exercise price of options as percentage	25.00%
2019 Equity Incentive Plan | Employees | After 2nd year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	3 years
2019 Equity Incentive Plan | Employees and non - employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights	Subsequent option grants to employees and grants to non-employees typically vest monthly over a four-year period. The majority of options outstanding at December 31, 2019, had vesting periods of four years.
Options vesting period	4 years
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of eligible earnings withholding	15.00%
Percentage of price of common stock purchased under ESPP	85.00%
Common stock initially reserved for ESPP	288,938
Unrecognized compensation expense	$ 0.9

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding Options
Balances, beginning balance	3,597,638
Options granted	2,362,266
Options exercised	(362,275)
Options forfeited	(343,360)
Balances, ending balance	5,254,269	3,597,638
Options vested and exercisable as of December 31, 2019	1,060,942
Weighted Average Exercise Price Per Share
Balances, beginning balance	$ 4.40
Options granted	27.22
Options exercised	2.78
Options forfeited	7.15
Balances, ending balance	14.59	$ 4.40
Options vested and exercisable as of December 31, 2019	$ 4.60
Weighted average remaining contractual term
Weighted average remaining contractual term	9 years	9 years 6 months
Options vested and exercisable as of December 31, 2019	8 years 6 months
Aggregate Value Intrinsic
Balances	$ 250,611	$ 15,056
Options vested and exercisable as of December 31, 2019	$ 61,203

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Fair Values of Employee Stock Options Granted (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	2.13%
Risk-free interest rate. minimum		2.61%	1.94%
Risk-free interest rate. maximum		3.10%	2.22%
Volatility	79.80%		91.30%
Expected term (in years)	6 years 18 days
Expected dividend yield rate	0.00%
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate. minimum	1.55%
Risk-free interest rate. maximum	2.13%
Volatility, minimum	70.60%
Volatility, maximum	76.20%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility		80.40%
Expected term (in years)		5 years 9 months 7 days	5 years
Minimum | 2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility		82.50%
Expected term (in years)		6 years 29 days	6 years 29 days
Maximum | 2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years

Stockholders' Equity - Schedu_3

Stockholders' Equity - Schedule of Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 12,706	$ 1,147	$ 344
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	6,075	556	184
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 6,631	$ 591	$ 160

Stockholders' Equity - Schedu_4

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Conversion of preferred stock outstanding		16,993,194
Common stock options outstanding	5,254,269	3,597,638
Options to purchase common stock available for issuance under equity incentive plan	2,633,874	1,816,266
Shares available for purchase under employee stock purchase plan	278,304
Total	8,166,447	22,407,098

Defined Contribution Benefit _2

Defined Contribution Benefit Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Defined contribution plan name	401(k)
Defined contribution plan, cost	$ 500,000	$ 200,000	$ 21,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Income Taxes [Line Items]
Provision for federal or state income taxes	$ 0	$ 0
Increase in valuation allowance	22,300,000
Benefit recognized for net operating loss carryforwards	0
Federal net operating loss carryforwards	105,800,000
State net operating loss carryforwards	$ 111,600,000
Federal and state net operating loss carryforwards expiration year	2033
Federal research and development tax credits	$ 1,000,000
State research and development tax credits	1,700,000
Federal Orphan Drug tax credits	$ 12,900,000
Federal research tax credit carry forwards expiration year start	2035
Orphan drug credit carryforwards expiration year	2037
Unrecognized tax benefits	$ 14,816,000	7,488,000	$ 4,733,000	$ 954,000
Accrual for interest and penalties related to unrecognized tax benefits	$ 0
Cumulative change in ownership minimum limited percentage of net operating loss and credit carryforwards	50.00%
Unrecognized tax benefits would reduce annual effective tax rate, if recognized	$ 12,600,000
State of California
Schedule Of Income Taxes [Line Items]
Unrecognized tax benefits	14,800,000
C Corporations | State of California
Schedule Of Income Taxes [Line Items]
Provision for federal or state income taxes	$ 800	$ 800

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	21.00%	21.00%	34.00%
Permanent items and other		(2.40%)	(9.40%)
Stock based compensation	1.60%	(0.80%)	(0.30%)
Research and development tax credits	1.60%	1.10%	(1.20%)
Orphan drug tax credit	6.80%	6.50%	13.10%
Tax Cuts and Jobs Act			(16.40%)
Valuation allowance	(31.00%)	(25.40%)	(19.80%)

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 carryforwards	$ 22,226	$ 8,474
Research and development credits	1,521	353
Orphan drug credit	8,657	3,781
Accrued liabilities	1,073	287
Right of use asset	1,062
Stock based compensation	1,909
Other, net		115
Total deferred tax assets	36,448	13,010
Deferred tax liabilities
Fixed assets	(154)	(7)
Lease liabilities	(944)
Deferred Tax Liabilities, Gross	(1,098)	(7)
Total	35,350	13,003
Less: valuation allowance	(35,350)	(13,003)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Beginning balance	$ 7,488	$ 4,733	$ 954
Additions (reductions) for tax positions taken in prior years	41	(118)	(34)
Additions for tax positions taken in current year	7,287	2,873	3,813
Ending balance	$ 14,816	$ 7,488	$ 4,733

Selected Quarterly Financial _3

Selected Quarterly Financial Information (Unaudited) - Summary of Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Loss from operations	$ (23,065)	$ (22,140)	$ (18,454)	$ (14,065)	$ (9,479)	$ (6,129)	$ (5,172)	$ (4,860)	$ (77,724)	$ (25,640)	$ (16,729)
Net loss	$ (20,959)	$ (20,483)	$ (17,142)	$ (13,547)	$ (9,018)	$ (5,997)	$ (5,037)	$ (4,733)	$ (72,131)	$ (24,785)	$ (16,593)
Net loss per share, basic and diluted	$ (0.58)	$ (0.63)	$ (0.70)	$ (3.97)	$ (2.64)	$ (1.77)	$ (1.49)	$ (1.41)	$ (2.99)	$ (7.31)	$ (4.97)
Weighted-average common shares outstanding, basic and diluted	35,851,252	32,312,814	24,479,767	3,413,760	3,409,874	3,394,423	3,380,899	3,368,608	24,124,924	3,388,586	3,337,640

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Scenario Forecast | Consulting Agreement
Subsequent Event [Line Items]
Cash severance expense	$ 1.2