Turning Point Therapeutics (TPTX) 10-K 1 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 23, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
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	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		48,979,903
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	Yes
Entity Public Float			$ 2,411
ICFR Auditor Attestation Flag	true
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 2021 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, 2020.

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 554,101	$ 48,188
Marketable securities	568,407	360,963
Prepaid and other current assets	8,171	5,796
Total current assets	1,130,679	414,947
Property and equipment, net	2,604	2,689
Right-of-use lease assets	3,357	4,493
Other assets	73	73
Total assets	1,136,713	422,202
Current liabilities:
Accounts payable	5,225	2,150
Accrued expenses and other current liabilities	9,183	3,910
Accrued compensation	8,588	6,736
Current portion of operating lease liabilities	1,396	1,236
Total current liabilities	24,392	14,032
Operating lease liabilities, long-term	2,423	3,819
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.0001 par value;10,000,000 shares authorized at December 31, 2020 and December 31, 2019, zero shares outstanding at December 31, 2020 and December 31, 2019
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2020 and December 31, 2019; 48,678,540 and 35,915,119 shares issued and outstanding at December 31, 2020 and December 31, 2019, respectively	5	4
Additional paid-in capital	1,389,860	526,960
Accumulated other comprehensive income	209	271
Accumulated deficit	(280,176)	(122,884)
Total stockholders' equity	1,109,898	404,351
Total liabilities and stockholders’ equity	$ 1,136,713	$ 422,202

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	48,678,540	35,915,119
Common stock, shares outstanding	48,678,540	35,915,119

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 25,000
Operating expenses:
Research and development	113,411	$ 57,943	$ 21,062
General and administrative	73,425	19,781	4,578
Total operating expenses	186,836	77,724	25,640
Loss from operations	(161,836)	(77,724)	(25,640)
Other income, net	4,544	5,593	855
Net loss	(157,292)	(72,131)	(24,785)
Unrealized gain (loss) on marketable securities, net of tax	(62)	271
Comprehensive loss	$ (157,354)	$ (71,860)	$ (24,785)
Net loss per share, basic and diluted	$ (3.85)	$ (2.99)	$ (7.31)
Weighted-average common shares outstanding, basic and diluted	40,843,782	24,124,924	3,388,586

Statements of Changes in Conver

Statements of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Series D Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
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
Balance at Dec. 31, 2018		$ 145,916
Balance, Shares at Dec. 31, 2018				3,411,516
Issuance of common stock in connection with a public offerings, 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
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 (loss)	271					$ 271
Balance at Dec. 31, 2019	$ 404,351			$ 4	526,960	271	(122,884)
Balance, Shares at Dec. 31, 2019	35,915,119			35,915,119
Issuance of common stock in connection with a public offerings, net of underwriting discounts, commissions, and offering costs	$ 785,469			$ 1	785,468
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, Shares				11,516,524
Option exercises	$ 12,237				12,237
Option exercises, Shares	1,218,410			1,218,410
Shares issued under employee stock purchase plan	$ 1,032				1,032
Shares issued under employee stock purchase plan, Shares				28,487
Stock-based compensation expense	64,163				64,163
Net loss	(157,292)						(157,292)
Other comprehensive income (loss)	(62)					(62)
Balance at Dec. 31, 2020	$ 1,109,898			$ 5	$ 1,389,860	$ 209	$ (280,176)
Balance, Shares at Dec. 31, 2020	48,678,540			48,678,540

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (157,292)	$ (72,131)	$ (24,785)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	64,163	12,706	1,147
Depreciation	875	492	138
Accretion of premium (discount) on marketable securities	1,261	(1,357)
Amortization of right-of-use operating lease asset	1,518	1,087
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,374)	(5,302)	53
Accounts payable	3,549	903	(119)
Accrued expenses and other current liabilities	3,655	522	(945)
Accrued compensation	1,852	5,323	978
Net cash used in operating activities	(82,793)	(57,757)	(23,533)
Investing activities
Purchases of marketable securities	(618,973)	(432,173)
Sales and maturities of marketable securities	410,205	72,838
Purchases of property and equipment	(1,264)	(1,744)	(302)
Net cash used in investing activities	(210,032)	(361,079)	(302)
Financing activities
Proceeds from issuance of common stock in initial public offering, net		175,151
Proceeds from issuance of common stock in public offerings, net of offering costs	785,469	189,505
Proceeds from issuance of convertible preferred stock, net of issuance costs			79,755
Proceeds from issuance of common stock under equity incentive plans	13,269	1,339	76
Net cash provided by financing activities	798,738	365,995	79,831
Net increase (decrease) in cash and cash equivalents	505,913	(52,841)	55,996
Cash and cash equivalents at the beginning of period	48,188	101,029	45,033
Cash and cash equivalents at the end of period	554,101	48,188	101,029
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 a 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, 2020
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 in October 2013, and commenced operations in 2014. The Company is clinical-stage precision oncology 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 In May 2020, the Company completed a public offering under which it sold 6,229,167 shares of common stock at an offering price of $60.00 per share. The net proceeds from this offering, after deducting underwriting discounts, commissions, and offering costs, were $351.6 million. In October 2020, the Company completed a public offering under which it sold 5,287,357 shares of common stock at an offering price of $87.00 per share. The net proceeds from this offering, after deducting underwriting discounts, commissions, and offering costs, were approximately $433.9 million. 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, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Revenue The Company recognizes revenue in accordance with Accounting Standards Codification (ASC) Topic 606, Revenue From Contracts With Customers The Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). In assessing whether a promised good or service is distinct, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, an entity is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (SSP) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, either at a point in time or over time, and if over time, recognition is based on the use of an output or input method. 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 determining the SSP of performance obligations associated with license arrangements, preclinical and clinical trial costs and accruals and stock-based compensation costs . 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, 2020 and 2019, 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 two 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 its operations, as necessary. Allowance for Credit Losses The Company segments its portfolio based on the underlying risk profiles of their current securities being held. The Company regularly reviews the securities in an unrealized loss position and evaluates the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, current and expected future economic conditions. As of December 31, 2020, the Company did not record an allowance for credit loss related to its investment portfolio. 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 the Company’s cash, cash equivalents, and marketable securities are held at two financial institutions. Due to the financial strength of the depository institutions, the Company believes 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, 2020 , cash and cash equivalents and marketable securities totaling $1,122.3 million are either not subject to FDIC insurance, or exceed the FDIC insured limit. The Company’s cash and cash equivalents and marketable securities are invested in short term, high grade securities, and as a result, the Company believes 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, 2020, 2019 and 2018. 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, 2020 and 2019, the Company has determined that these expenses have not met the criteria to be capitalized. 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. Clinical Trial Costs and Accruals A significant portion of the Company’s clinical trial costs relate to contracts with contract research organizations (CROs). The financial terms of the Company’s CRO contracts may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate clinical trial expenses in the Company’s financial statements by matching those expenses with the period in which services and efforts are expended. As part of the process of preparing the Company’s financial statements, the Company evaluates cost information provided by the Company’s CROs concerning estimated monthly expenses for services rendered and unbilled obligations as the sponsor of the Company’s clinical trials. Accordingly, the Company’s clinical trial accrual is dependent upon the timely and accurate reporting of CROs and other third-party vendors, and the Company’s ability to accurately estimate any unbilled obligations. If the contracted amounts are modified, for instance, as a result of changes in the clinical trial protocol or scope of work to be performed, the Company’s modifies its accruals accordingly on a prospective basis. Revisions in the scope of a contract are charged to research and development expense in the period in which the facts that give rise to the revision become reasonably certain. 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 Expense For purposes of calculating stock-based compensation expense, 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 restricted stock units. The Company excluded stock options to purchase common stock, restricted stock units and from the number of shares used to calculate diluted shares outstanding because the inclusion of these potentially dilutive securities would have been antidilutive . Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2020 2019 2018 Convertible preferred stock (as converted) – - 16,993,194 Common stock options 5,790,713 5,254,269 3,597,638 RSUs 21,500 - - Total 5,812,213 5,254,269 20,590,832 Recently Adopted Accounting Standards Updates In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses ASU 2016-13 a material impact to the Company’s financial position, results of operations and cash flows. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement comprehensive income. T he Company adopted the new standard beginning January 1, 2020 and the adoption had an immaterial impact to the Company’s financial position, results of operations and cash flows.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2020
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, 2020, marketable securities consisted of the following (in thousands): Unrealized Maturity in Years Amortized Cost Gains Losses Fair Value U.S. Treasuries 2 years or less 113,662 19 (1 ) 113,680 U.S. Government agency securities 2 years or less 173,583 100 - 173,683 Corporate debt securities 2 years or less 169,189 103 (27 ) 169,265 Commercial paper Less than 1 111,779 - - 111,779 Total marketable securities $ 568,213 $ 222 $ (28 ) $ 568,407 The Company’s investments in corporate debt securities in an unrealized loss position at December 31, 2020 are of high credit quality (rated A or higher). Unrealized losses on these investments were primarily due to changes in interest rates. The Company does not intend to sell these investments and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost basis. 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

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
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, 2020 Using: Level 1 Level 2 Level 3 Total Money market funds $ 299,571 $ - $ - $ 299,571 U.S. Treasuries 113,680 - - 113,680 U.S. Government agency securities - 173,683 - 173,683 Corporate debt securities - 180,718 - 180,718 Commercial paper - 354,223 - 354,223 Total cash equivalents and marketable securities $ 413,251 $ 708,624 $ - $ 1,121,875 Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Money market funds $ 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 cash equivalents and marketable securities $ 45,085 $ 360,963 $ - $ 406,048

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Laboratory equipment $ 1,629 $ 885 Computer equipment and software 956 910 Tenant improvements 1,108 1,108 Furniture and fixtures 357 357 Property and equipment 4,050 3,260 Less: accumulated depreciation (1,446 ) (571 ) Property and equipment, net $ 2,604 $ 2,689 Depreciation expense for the years ended December 31, 2020, 2019 and 2018 was $0.9 million, $0.5 million and $0.1 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Accrued research and development expenses $ 8,457 $ 3,414 Accrued general and administrative expenses 682 451 Other current liabilities 44 45 Total $ 9,183 $ 3,910

Zai Repotrectinib Agreement

Zai Repotrectinib Agreement	12 Months Ended
	Dec. 31, 2020
Research And Development [Abstract]
Zai Repotrectinib Agreement	7. Zai Repotrectinib Agreement Terms of Agreement On July 6, 2020, the Company entered into a License Agreement (the Zai Repotrectinib Agreement) with Zai Lab (Shanghai) Co., Ltd. (Zai), pursuant to which the Company grants Zai exclusive rights to develop and commercialize products containing the Company’s drug candidate, repotrectinib (the Products), in Mainland China, Hong Kong, Macau and Taiwan (each, a region and collectively, the Territory). The Company retains exclusive rights to, among other things, develop, manufacture and commercialize the Products outside the Territory. The Company will supply or have supplied to Zai the Products for use in the Territory pursuant to a supply agreement for agreed upon consideration, except that Zai has the right, at its election, to package and label the Products in or outside the Territory for use in the Territory In addition, during the term of the Zai Repotrectinib Agreement, Zai will be obligated to pay the Company tiered percentage royalties ranging from teens on annual net sales of the Products in the Territory, subject to adjustments in specified circumstances Zai will be responsible for conducting the development and commercialization activities in the Territory related to the Products at Zai’s own expense, subject to limited exceptions pursuant to which the Company may be responsible for the cost. The Company will be responsible for global clinical studies of the Products, including the portions that may be conducted in the Territory, at the Company’s expense, except that Zai will participate in global clinical studies of the Products through clinical trial sites in the Territory as agreed as of the effective date of the Zai Repotrectinib Agreement The Zai Repotrectinib Agreement Zai Repotrectinib Agreement Zai Repotrectinib Agreement Zai Repotrectinib Agreement Zai Repotrectinib Agreement Pursuant to the terms of the Zai Repotrectinib Agreement, Zai Repotrectinib Agreement Revenue Recognition The Company determined that two performance obligations existed: (1) the exclusive license, bundled with the associated know-how and (2) the Company's initial obligation to supply repotrectinib for clinical development in the Territory. The total transaction price of $25.7 million was allocated to the performance obligations on the basis of the relative stand-alone selling price estimated for each performance obligation. In estimating the stand-alone selling price for each performance obligation, the Company developed assumptions that require judgment and included forecasted revenues, expected development timelines, discount rates, probabilities of technical and regulatory success and costs for manufacturing clinical supplies. The Company delivered the license and technical know-how to Zai in the third quarter of 2020 to satisfy this performance obligation, and accordingly the Company recognized license revenue of $25.0 million in the third quarter of 2020. The $0.7 million in consideration allocable to the clinical supply performance obligation will be recognized when clinical trial material has been shipped by the Company and Zai obtains control of the goods, upon delivery, over the period of the obligation. As of December 31, 2020, the Company has not recognized any revenue associated with the clinical supply performance obligation. The Company assessed the Zai Repotrectinib Agreement to determine whether a financing component exists and concluded that a significant financing component does not exist. The upfront payment received by the was subject to foreign tax withholdings. The Company recorded this tax expense to general and administrative expense in the Statements of Operations and Comprehensive Loss.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Operating Leases The Company has one lease agreement for the leasing of office and laboratory space with an initial lease term of four years resulting in an initial 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 2019. The right-of-use asset and corresponding lease liability was estimated assuming a remaining lease term of 48 months and an estimated discount rate of 8.5%, which was the Company’s incremental borrowing rate at the date of the lease commencement. Future minimum payments under the lease as of December 31, 2020 are as follows (in thousands) 2021 1,668 2022 1,718 2023 872 Total future minimum lease payments 4,258 Less: amounts representing interest (439 ) Total lease liability $ 3,819 Remaining lease term 2.5 years Rent expense for the years ended December 31, 2020, 2019 and 2018 was approximately $1.5 million, and $1.1 million and $0.5 million, respectively elated to its operating lease agreement of $1.6 million, $1.2 million and $0.4 million for the years ended December 31, 2020, 2019 and 2018, respectively

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity Stock Option Plan At the Market Offering In August 2020, the Company entered into an Open Market Sale Agreement with Jefferies LLC, or ATM facility, under which the Company may offer and sell, from time to time, at its sole discretion, up to $250.0 million shares of the Company’s common stock. To date, the Company has not yet sold any shares of common stock under the ATM facility. Stock Option Plan T In addition, the number of shares of common stock available for issuance under the Plan will be automatically increased on the first day of each calendar year during the ten-year term of the Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 4% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. On January 1, 2020, the Company added 1,436,604 shares to the Plan. 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 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, 2020 , had vesting periods of four years . The weighted-average grant-date fair value of options granted to employees was $46.00, $21.66 and $6.23 for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, unrecognized compensation expense related to unvested options was $110.9 million and is expected to be recognized over a weighted average term of 2.60 years. The following summarizes option activity for the year ended December 31, 2020: Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2019 5,254,269 $ 14.59 9.0 $ 250,611 Options granted 2,167,920 $ 67.64 Options exercised (1,218,410 ) $ 10.04 Options forfeited or cancelled (413,066 ) $ 20.81 Balance as of December 31, 2020 5,790,713 $ 34.97 8.4 $ 503,114 Options vested and exercisable as of December 31, 2020 2,002,242 $ 18.50 7.7 $ 206,932 The fair values of the employee stock options granted during 2020, 2019 and 2018 was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 1.15 % 2.13 % 2.61 - 3.10% Volatility 79.5 % 79.8 % 80.4 - 82.5% Expected term (in years) 6.07 6.05 5.77 - 6.08 Dividend yield - - - Restricted Stock Units The summary of the Company’s restricted stock unit activity for the periods presented is as follows: Number of Restricted Stock Units Outstanding Weighted Average Grant Date Fair Value Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2019 - $ - Granted 21,500 $ 59.94 Vested - $ - Forfeited - $ - Outstanding as of December 31, 2020 21,500 $ 59.94 $ 2,620 No 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, 2020, unrecognized compensation expense related to the ESPP was $1.4 million. The assumptions used for the year ended December 31, 2020 and the resulting estimates of weighted-average fair value per share for stock purchased under the ESPP during 2020 were as follows : Year Ended December 31, 2020 2019 Risk-free interest rate 0.08 – 0.19% 1.55 - 2.13% Volatility 79.7 - 91.6% 70.6 - 76.2% Expected term (in years) 0.50 - 2.00 0.50 - 2.00 Dividend yield - - Departure of Former Chief Scientific Officer (CSO) On January 9, 2020, the Company entered into a Transition Separation and Consulting Agreement (the Transition Agreement) with the Company’s former CSO, Dr. Jingrong Jean Cui. In connection with this Transition Agreement, Dr. Cui resigned from her position as CSO effective January 31, 2020 and thereafter agreed to serve as a consultant to the Company on an as needed basis until June 30, 2020 The Company determined that the modification to extend the term of vested stock options was a Type I modification pursuant to ASC 718, Compensation – Stock Compensation Stock-based compensation expense Stock-based compensation expense resulting from grants under the Company’s equity incentive plan and employee stock purchase plan is reflected in the statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 15,539 $ 6,075 $ 556 General and administrative 48,624 6,631 591 Total stock-based compensation expense $ 64,163 $ 12,706 $ 1,147 Common Stock Reserved for Future Issuance Common stock reserved for future issuance consists of the following: December 31, 2020 2019 Common stock options outstanding 5,790,713 5,254,269 RSUs outstanding 21,500 - Options to purchase common stock available for issuance under the Plan 2,294,124 2,633,874 Shares available for purchase under ESPP 249,817 278,304 Total 8,356,154 8,166,447

Defined Contribution Benefit Pl

Defined Contribution Benefit Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Benefit Plan	10. 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 $0.8 million, $0.5 million and $0.2 million in matching contributions for the years ended December 31, 2020, 2019 and 2018, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes No provision for federal or state income taxes has been recorded for the years ended December 31, 2020, 2019 and 2018 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, 2020 2019 2018 Tax computed at federal statutory rate 21.0 % 21.0 % 21.0 % Permanent items — — (2.4 ) Stock based compensation (1.7 ) 1.6 (0.8 ) Research and development tax credits 2.5 1.6 1.1 Orphan drug tax credit 4.4 6.8 6.5 Other (0.1 ) — — Valuation allowance (26.1 ) (31.0 ) (25.4 ) Effective income tax rate — % — % — % Deferred tax assets and liabilities consist of the following (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 47,411 $ 22,226 Research and development credits 5,415 1,521 Orphan drug credit 15,622 8,657 Accrued liabilities 1,552 1,073 Right of use asset 802 1,062 Stock-based compensation expense 6,386 1,909 Other, net 2 — Total deferred tax assets 77,190 36,448 Deferred tax liabilities Fixed assets (124 ) (154 ) Lease liabilities (705 ) (944 ) (829 ) (1,098 ) Total 76,361 35,350 Less: valuation allowance (76,361 ) (35,350 ) Net deferred tax assets $ — $ — The valuation allowance increased by $41.0 million during the year ended December 31, 2020. 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, 2020, the Company has federal and state net operating loss carryforwards of approximately $225.8 million and $111.5 million, respectively. Portions of the federal and state tax loss carryforwards will begin to expire in 2033 if not utilized. The $205.3 million of the federal net operating loss carryforwards generated post 2017 can be carried forward indefinitely. At December 31, 2020, the Company has federal and state research and development tax credits of approximately $3.2 million and $4.6 million, respectively. At December 31, 2020, the Company has federal Orphan Drug tax credits of approximately $20.6 million. If not utilized, the federal research tax credit will begin to expire in 2035 and the Orphan Drug credit will begin to expire in 2037. The California research tax credit can be carried forward indefinitely. 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 completed an analysis under IRC Sections 382 and 383 through June 30, 2020. The Company experienced ownership changes in 2013, 2015, and 2017, but the ownership changes did not result in a material forfeiture of tax attributes. The Company has not completed its analysis to determine whether our net operating loss and credit carryforwards generated in the last 6-months of the tax year ending December 31, 2020, are subject to an annual limitation under Sections 382 or 383 of the Code. Once the Section 382 analysis is updated through December 31, 2020, any limitations on the net operating loss and credit carryforwards will be updated through December 31, 2020. Total unrecognized income tax benefits related to California net operating losses, federal and California research and development and federal Orphan drug tax credit carryforwards were approximately $16.5 million at December 31, 2020. 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, 2020, 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. 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. At December 31, 2019, and December 31, 2020, the unrecognized tax benefits recorded were approximately $14.8 million and $16.5 million, respectively. Approximately $14.2 million of the unrecognized tax benefits would reduce our 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, 2020 2019 Beginning balance $ 14,825 $ 7,488 Additions (Reductions) for tax positions taken in prior years (869 ) 50 Additions for tax positions taken in current year 2,517 7,287 Ending balance $ 16,473 $ 14,825 The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates including U.S. Federal and California. 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 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, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	12. Selected Quarterly Financial Information (Unaudited) The following is a summary of the quarterly results of the Company for the years ended December 31, 2020 and 2019 ( ): Three months ended, 12/31/2020 9/30/2020 6/30/2020 3/31/2020 Loss from operations (47,939 ) (18,539 ) (32,732 ) (62,626 ) Net loss (47,376 ) (17,705 ) (31,493 ) (60,718 ) Net loss per share, basic and diluted $ (1.02 ) $ (0.42 ) $ (0.82 ) $ (1.69 ) Weighted-average common shares outstanding, basic and diluted 46,588,835 42,185,824 38,603,236 35,919,358 Three months ended, 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

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events On January 10, 2021, the Company entered into a License Agreement (the Zai TPX-0022 Agreement) with Zai Lab (Shanghai) Co., Ltd. (Zai), pursuant to which the Company granted Zai exclusive rights to develop and commercialize products containing the Company’s drug candidate TPX-0022 (the TPX-0022 Products), Pursuant to the terms of the , the Company will receive an upfront cash payment of $25.0 million and will be eligible to receive up to approximately $336.0 million in development and sales milestone payments, consisting of up to approximately $121.0 million of development milestones and up to $215.0 million of sales milestones. In addition, during the term of the , Zai will pay the Company tiered percentage royalties ranging from mid-teens to low twenties on annual net sales of the Products in the Territory, subject to adjustments in specified circumstances

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Revenue	Revenue The Company recognizes revenue in accordance with Accounting Standards Codification (ASC) Topic 606, Revenue From Contracts With Customers The Company assesses the goods or services promised within each contract and determines those that are performance obligations. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The Company assesses whether each promised good or service is distinct for the purpose of identifying the performance obligations in the contract. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (that is, the good or service is capable of being distinct) and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (that is, the promise to transfer the good or service is distinct within the context of the contract). In assessing whether a promised good or service is distinct, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, an entity is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (SSP) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied, either at a point in time or over time, and if over time, recognition is based on the use of an output or input method.
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 determining the SSP of performance obligations associated with license arrangements, preclinical and clinical trial costs and accruals and stock-based compensation costs .
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, 2020 and 2019, 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 two 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 its operations, as necessary.
Allowance for Credit Losses	Allowance for Credit Losses The Company segments its portfolio based on the underlying risk profiles of their current securities being held. The Company regularly reviews the securities in an unrealized loss position and evaluates the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, current and expected future economic conditions. As of December 31, 2020, the Company did not record an allowance for credit loss related to its investment portfolio.
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 the Company’s cash, cash equivalents, and marketable securities are held at two financial institutions. Due to the financial strength of the depository institutions, the Company believes 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, 2020 , cash and cash equivalents and marketable securities totaling $1,122.3 million are either not subject to FDIC insurance, or exceed the FDIC insured limit. The Company’s cash and cash equivalents and marketable securities are invested in short term, high grade securities, and as a result, the Company believes 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, 2020, 2019 and 2018.
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, 2020 and 2019, the Company has determined that these expenses have not met the criteria to be capitalized.
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.
Clinical Trial Costs and Accruals	Clinical Trial Costs and Accruals A significant portion of the Company’s clinical trial costs relate to contracts with contract research organizations (CROs). The financial terms of the Company’s CRO contracts may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company’s objective is to reflect the appropriate clinical trial expenses in the Company’s financial statements by matching those expenses with the period in which services and efforts are expended. As part of the process of preparing the Company’s financial statements, the Company evaluates cost information provided by the Company’s CROs concerning estimated monthly expenses for services rendered and unbilled obligations as the sponsor of the Company’s clinical trials. Accordingly, the Company’s clinical trial accrual is dependent upon the timely and accurate reporting of CROs and other third-party vendors, and the Company’s ability to accurately estimate any unbilled obligations. If the contracted amounts are modified, for instance, as a result of changes in the clinical trial protocol or scope of work to be performed, the Company’s modifies its accruals accordingly on a prospective basis. Revisions in the scope of a contract are charged to research and development expense in the period in which the facts that give rise to the revision become reasonably certain.
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 Expense	Stock-Based Compensation Expense For purposes of calculating stock-based compensation expense, 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 restricted stock units. The Company excluded stock options to purchase common stock, restricted stock units and from the number of shares used to calculate diluted shares outstanding because the inclusion of these potentially dilutive securities would have been antidilutive . Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2020 2019 2018 Convertible preferred stock (as converted) – - 16,993,194 Common stock options 5,790,713 5,254,269 3,597,638 RSUs 21,500 - - Total 5,812,213 5,254,269 20,590,832
Recently Adopted Accounting Standards Updates	Recently Adopted Accounting Standards Updates In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses ASU 2016-13 a material impact to the Company’s financial position, results of operations and cash flows. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement comprehensive income. T he Company adopted the new standard beginning January 1, 2020 and the adoption had an immaterial impact to the Company’s financial position, results of operations and cash flows.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of Outstanding Anti-Dilutive Securities not Included in Diluted Net Loss Per Share Calculation	Historical outstanding anti-dilutive securities not included in the diluted net loss per share calculation include the following: Year Ended December 31, 2020 2019 2018 Convertible preferred stock (as converted) – - 16,993,194 Common stock options 5,790,713 5,254,269 3,597,638 RSUs 21,500 - - Total 5,812,213 5,254,269 20,590,832

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Marketable Securities	At December 31, 2020, marketable securities consisted of the following (in thousands): Unrealized Maturity in Years Amortized Cost Gains Losses Fair Value U.S. Treasuries 2 years or less 113,662 19 (1 ) 113,680 U.S. Government agency securities 2 years or less 173,583 100 - 173,683 Corporate debt securities 2 years or less 169,189 103 (27 ) 169,265 Commercial paper Less than 1 111,779 - - 111,779 Total marketable securities $ 568,213 $ 222 $ (28 ) $ 568,407 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, 2020
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, 2020 Using: Level 1 Level 2 Level 3 Total Money market funds $ 299,571 $ - $ - $ 299,571 U.S. Treasuries 113,680 - - 113,680 U.S. Government agency securities - 173,683 - 173,683 Corporate debt securities - 180,718 - 180,718 Commercial paper - 354,223 - 354,223 Total cash equivalents and marketable securities $ 413,251 $ 708,624 $ - $ 1,121,875 Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Money market funds $ 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 cash equivalents and marketable securities $ 45,085 $ 360,963 $ - $ 406,048

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Laboratory equipment $ 1,629 $ 885 Computer equipment and software 956 910 Tenant improvements 1,108 1,108 Furniture and fixtures 357 357 Property and equipment 4,050 3,260 Less: accumulated depreciation (1,446 ) (571 ) Property and equipment, net $ 2,604 $ 2,689

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Accrued research and development expenses $ 8,457 $ 3,414 Accrued general and administrative expenses 682 451 Other current liabilities 44 45 Total $ 9,183 $ 3,910

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Summary of Operating Leases Future Minimum Payments	Future minimum payments under the lease as of December 31, 2020 are as follows (in thousands) 2021 1,668 2022 1,718 2023 872 Total future minimum lease payments 4,258 Less: amounts representing interest (439 ) Total lease liability $ 3,819 Remaining lease term 2.5 years

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Option Activity	The following summarizes option activity for the year ended December 31, 2020: Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2019 5,254,269 $ 14.59 9.0 $ 250,611 Options granted 2,167,920 $ 67.64 Options exercised (1,218,410 ) $ 10.04 Options forfeited or cancelled (413,066 ) $ 20.81 Balance as of December 31, 2020 5,790,713 $ 34.97 8.4 $ 503,114 Options vested and exercisable as of December 31, 2020 2,002,242 $ 18.50 7.7 $ 206,932
Schedule of Fair Values of Employee Stock Options Granted	The fair values of the employee stock options granted during 2020, 2019 and 2018 was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 1.15 % 2.13 % 2.61 - 3.10% Volatility 79.5 % 79.8 % 80.4 - 82.5% Expected term (in years) 6.07 6.05 5.77 - 6.08 Dividend yield - - - The assumptions used for the year ended December 31, 2020 and the resulting estimates of weighted-average fair value per share for stock purchased under the ESPP during 2020 were as follows : Year Ended December 31, 2020 2019 Risk-free interest rate 0.08 – 0.19% 1.55 - 2.13% Volatility 79.7 - 91.6% 70.6 - 76.2% Expected term (in years) 0.50 - 2.00 0.50 - 2.00 Dividend yield - -
Summary of Restricted Stock Unit Activity	The summary of the Company’s restricted stock unit activity for the periods presented is as follows: Number of Restricted Stock Units Outstanding Weighted Average Grant Date Fair Value Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2019 - $ - Granted 21,500 $ 59.94 Vested - $ - Forfeited - $ - Outstanding as of December 31, 2020 21,500 $ 59.94 $ 2,620
Schedule of Stock Based Compensation Expense	Stock-based compensation expense resulting from grants under the Company’s equity incentive plan and employee stock purchase plan is reflected in the statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 15,539 $ 6,075 $ 556 General and administrative 48,624 6,631 591 Total stock-based compensation expense $ 64,163 $ 12,706 $ 1,147
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance consists of the following: December 31, 2020 2019 Common stock options outstanding 5,790,713 5,254,269 RSUs outstanding 21,500 - Options to purchase common stock available for issuance under the Plan 2,294,124 2,633,874 Shares available for purchase under ESPP 249,817 278,304 Total 8,356,154 8,166,447

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2018 Tax computed at federal statutory rate 21.0 % 21.0 % 21.0 % Permanent items — — (2.4 ) Stock based compensation (1.7 ) 1.6 (0.8 ) Research and development tax credits 2.5 1.6 1.1 Orphan drug tax credit 4.4 6.8 6.5 Other (0.1 ) — — Valuation allowance (26.1 ) (31.0 ) (25.4 ) Effective income tax rate — % — % — %
Summary of Deferred Tax Assets and Liabilities	Deferred tax assets and liabilities consist of the following (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 47,411 $ 22,226 Research and development credits 5,415 1,521 Orphan drug credit 15,622 8,657 Accrued liabilities 1,552 1,073 Right of use asset 802 1,062 Stock-based compensation expense 6,386 1,909 Other, net 2 — Total deferred tax assets 77,190 36,448 Deferred tax liabilities Fixed assets (124 ) (154 ) Lease liabilities (705 ) (944 ) (829 ) (1,098 ) Total 76,361 35,350 Less: valuation allowance (76,361 ) (35,350 ) 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, 2020 2019 Beginning balance $ 14,825 $ 7,488 Additions (Reductions) for tax positions taken in prior years (869 ) 50 Additions for tax positions taken in current year 2,517 7,287 Ending balance $ 16,473 $ 14,825

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 and 2019 ( ): Three months ended, 12/31/2020 9/30/2020 6/30/2020 3/31/2020 Loss from operations (47,939 ) (18,539 ) (32,732 ) (62,626 ) Net loss (47,376 ) (17,705 ) (31,493 ) (60,718 ) Net loss per share, basic and diluted $ (1.02 ) $ (0.42 ) $ (0.82 ) $ (1.69 ) Weighted-average common shares outstanding, basic and diluted 46,588,835 42,185,824 38,603,236 35,919,358 Three months ended, 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

Formation and Business of the_2

Formation and Business of the Company - Additional Information (Details) $ / shares in Units, $ in Millions	Oct. 08, 2013Segment	Oct. 31, 2020USD ($)$ / sharesshares	May 31, 2020USD ($)$ / sharesshares
Basis Of Presentation [Line Items]
Number of operating segments | Segment	1
Number of common stock, shares sold | shares			6,229,167
Offering price per share | $ / shares			$ 60
Net proceeds from offering after deducting underwriting discounts, commissions and offering costs | $			$ 351.6
October 2020 Public Offering
Basis Of Presentation [Line Items]
Number of common stock, shares sold | shares		5,287,357
Offering price per share | $ / shares		$ 87
Net proceeds from offering after deducting underwriting discounts, commissions and offering costs | $		$ 433.9

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Allowance for credit loss	$ 0
Exceed of federal deposits insurance limit	1,122,300,000
Impairment of long-lived assets	$ 0	$ 0	$ 0
Stock options expected contractual term	6 years 25 days	6 years 18 days
Expected dividend yield rate	0.00%
ASU 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life	3 years
Stock options expected contractual term			5 years 9 months 7 days
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
Arithmetic Average
Significant Accounting Policies [Line Items]
Stock options expected contractual term	10 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Outstanding Anti-Dilutive Securities not Included in Diluted Net Loss Per Share Calculation (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share	5,812,213	5,254,269	20,590,832
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
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	5,790,713	5,254,269	3,597,638
RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share	21,500

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 568,213	$ 360,692
Unrealized Gains	222	312
Unrealized Losses	(28)	(41)
Fair Value	$ 568,407	$ 360,963
U.S. Treasuries
Marketable Securities [Line Items]
Maturity in Years	2 years or less
Amortized Cost	$ 113,662
Unrealized Gains	19
Unrealized Losses	(1)
Fair Value	$ 113,680
U.S. Government Agency Securities
Marketable Securities [Line Items]
Maturity in Years	2 years or less	2 years or less
Amortized Cost	$ 173,583	$ 90,596
Unrealized Gains	100	42
Unrealized Losses		(20)
Fair Value	$ 173,683	$ 90,618
Corporate Debt Securities
Marketable Securities [Line Items]
Maturity in Years	2 years or less	2 years or less
Amortized Cost	$ 169,189	$ 173,595
Unrealized Gains	103	178
Unrealized Losses	(27)	(21)
Fair Value	$ 169,265	$ 173,752
Commercial Paper
Marketable Securities [Line Items]
Maturity in Years	Less than 1	Less than 1
Amortized Cost	$ 111,779	$ 96,501
Unrealized Gains		92
Fair Value	$ 111,779	$ 96,593

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, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	$ 1,121,875	$ 406,048
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	299,571	45,085
U.S. Treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	113,680
U.S Government Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	173,683	90,618
Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	180,718	173,752
Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	354,223	96,593
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	413,251	45,085
Level 1 | Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	299,571	45,085
Level 1 | U.S. Treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	113,680
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	708,624	360,963
Level 2 | U.S Government Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	173,683	90,618
Level 2 | Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	180,718	173,752
Level 2 | Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and market securities	$ 354,223	$ 96,593

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,050	$ 3,260
Less: accumulated depreciation	(1,446)	(571)
Property and equipment, net	2,604	2,689
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,629	885
Computer Equipment And Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	956	910
Tenant Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,108	1,108
Furniture And Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 357	$ 357

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation	$ 875	$ 492	$ 138

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, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 8,457	$ 3,414
Accrued general and administrative expenses	682	451
Other current liabilities	44	45
Total	$ 9,183	$ 3,910

Zai Repotrectinib Agreement - A

Zai Repotrectinib Agreement - Additional Information (Details) - USD ($)	Jul. 06, 2020	Sep. 30, 2020	Dec. 31, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total transaction price allocated to performance obligation			$ 25,700,000
License
Research And Development Arrangement Contract To Perform For Others [Line Items]
Revenue recognized		$ 25,000,000
Clinical Supply
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total transaction price allocated to performance obligation			700,000
Revenue recognized			$ 0
Zai Repotrectinib Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront cash payment received	$ 25,000,000
Zai Repotrectinib Agreement | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments eligible to receive	151,000,000
Zai Repotrectinib Agreement | Development Milestones | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments eligible to receive	46,000,000
Zai Repotrectinib Agreement | Sales Milestones | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments eligible to receive	$ 105,000,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	Jul. 01, 2019USD ($)OperatingLease	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
Number of operating lease | OperatingLease	1
Operating lease, initial lease term	4 years
Operating lease, remaining lease term	48 months	2 years 6 months
Operating lease right-to-use liability	$ 4,000	$ 3,819
Operating lease, right-of-use asset	$ 3,700	3,357	$ 4,493
Operating lease, discount rate	8.50%
Deferred gain	$ 300
Rent expense		1,500	1,100	$ 500
Operating lease, cash payments		$ 1,600	$ 1,200	$ 400

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Operating Leases Future Minimum Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jul. 01, 2019
Commitments And Contingencies Disclosure [Abstract]
2021	$ 1,668
2022	1,718
2023	872
Total future minimum lease payments	4,258
Less: amounts representing interest	(439)
Operating lease right-to-use liability	$ 3,819	$ 4,000
Remaining lease term	2 years 6 months	48 months

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Aug. 01, 2020	Jan. 01, 2020	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance					2,294,124	2,633,874
Weighted-average grant-date fair value of options granted to employees					$ 46	$ 21.66	$ 6.23
Unrecognized compensation expense related to unvested options					$ 110,900
Unrecognized compensation expense, weighted-average period for recognition					2 years 7 months 6 days
Common stock initially reserved					8,356,154	8,166,447
Stock-based compensation expense					$ 64,163	$ 12,706	$ 1,147
General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense					$ 48,624	$ 6,631	$ 591
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense, weighted-average period for recognition					3 years 6 months 10 days
Number of awards vested					0
Unrecognized compensation expense related to unvested awards					$ 1,100
Chief Scientific Officer | Transition Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period				18 months
Cash severance expense			$ 1,200
Chief Scientific Officer | Transition Agreement | General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense			$ 31,400
Maximum | Chief Scientific Officer | Transition Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Extended options vesting period				12 months
Minimum | Chief Scientific Officer | Transition Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Extended options vesting period				90 days
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based award, description					The Company’s 2019 Equity Incentive Plan (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. In addition, the number of shares of common stock available for issuance under the Plan will be automatically increased on the first day of each calendar year during the ten-year term of the Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 4% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors.  On January 1, 2020, the Company added 1,436,604 shares to the Plan. As of December 31, 2020, the Plan had a maximum of 2,294,124 total shares available for issuance.
Term of plan					ten-year
Plan expiration date					Jan. 1, 2029
Percentage of outstanding common stock added to plan each year					4.00%
Number of shares added to plan		1,436,604
2019 Equity Incentive Plan | After 2nd year
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period					3 months
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 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, 2020, had vesting periods of four years.
Options vesting period					4 years
2019 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance					2,294,124
Options expiration period					10 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					288,938
Unrecognized compensation expense					$ 1,400
ATM Facility
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock authorized for issuance yet to issue	$ 250,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Outstanding Options
Balance as of December 31, 2019	5,254,269
Options granted	2,167,920
Options exercised	(1,218,410)
Options forfeited or cancelled	(413,066)
Balance as of December 31, 2020	5,790,713	5,254,269
Options vested and exercisable as of December 31, 2020	2,002,242
Weighted Average Exercise Price Per Share
Balance as of December 31, 2019	$ 14.59
Options granted	67.64
Options exercised	10.04
Options forfeited or cancelled	20.81
Balance as of December 31, 2020	34.97	$ 14.59
Options vested and exercisable as of December 31, 2020	$ 18.50
Weighted average remaining contractual term
Weighted average remaining contractual term	8 years 4 months 24 days	9 years
Options vested and exercisable as of December 31, 2020	7 years 8 months 12 days
Aggregate Value Intrinsic
Balances	$ 503,114	$ 250,611
Options vested and exercisable as of December 31, 2020	$ 206,932

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Fair Values of Employee Stock Options Granted (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.15%	2.13%
Risk-free interest rate. minimum			2.61%
Risk-free interest rate. maximum			3.10%
Volatility	79.50%	79.80%
Volatility, minimum			80.40%
Volatility, maximum			82.50%
Expected term (in years)	6 years 25 days	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	0.08%	1.55%
Risk-free interest rate. maximum	0.19%	2.13%
Volatility, minimum	79.70%	70.60%
Volatility, maximum	91.60%	76.20%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)			5 years 9 months 7 days
Minimum | 2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)			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	2 years

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Number of Restricted Stock Units Outstanding
Outstanding as of December 31, 2020	21,500
RSUs
Number of Restricted Stock Units Outstanding
Granted	21,500
Vested	0
Outstanding as of December 31, 2020	21,500
Weighted Average Grant Date Fair Value
Granted | $ / shares	$ 59.94
Outstanding as of December 31, 2020 | $ / shares	$ 59.94
Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2020 | $	$ 2,620

Stockholders' Equity - Schedu_3

Stockholders' Equity - Schedule of Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 64,163	$ 12,706	$ 1,147
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	15,539	6,075	556
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 48,624	$ 6,631	$ 591

Stockholders' Equity - Schedu_4

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock options outstanding	5,790,713	5,254,269
RSUs outstanding	21,500
Options to purchase common stock available for issuance under the Plan	2,294,124	2,633,874
Shares available for purchase under ESPP	249,817	278,304
Total	8,356,154	8,166,447

Defined Contribution Benefit _2

Defined Contribution Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Defined contribution plan, description	401(k)
Defined contribution plan, cost	$ 0.8	$ 0.5	$ 0.2

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Income Taxes [Line Items]
Provision for federal or state income taxes	$ 0	$ 0	$ 0
Increase in valuation allowance	41,000,000
Benefit recognized for net operating loss carryforwards	0
Federal net operating loss carryforwards	225,800,000			$ 205,300,000
State net operating loss carryforwards	$ 111,500,000
Federal and state tax loss carryforwards expiration year	2033
Federal research and development tax credits	$ 3,200,000
State research and development tax credits	4,600,000
Federal Orphan Drug tax credits	$ 20,600,000
Federal research tax credit carry forwards expiration year start	2035
Orphan drug credit carryforwards expiration year	2037
Cumulative change in ownership minimum limited percentage of net operating loss and credit carryforwards	50.00%
Unrecognized tax benefits	$ 16,473,000	14,825,000	7,488,000
Accrual for interest and penalties related to unrecognized tax benefits	0
Unrecognized tax benefits would reduce annual effective tax rate, if recognized	14,200,000
State of California
Schedule Of Income Taxes [Line Items]
Unrecognized tax benefits	16,500,000
C Corporations | State of California
Schedule Of Income Taxes [Line Items]
Provision for federal or state income taxes	$ 800	$ 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, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	21.00%	21.00%	21.00%
Permanent items			(2.40%)
Stock based compensation	(1.70%)	1.60%	(0.80%)
Research and development tax credits	2.50%	1.60%	1.10%
Orphan drug tax credit	4.40%	6.80%	6.50%
Other	(0.10%)
Valuation allowance	(26.10%)	(31.00%)	(25.40%)

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 47,411	$ 22,226
Research and development credits	5,415	1,521
Orphan drug credit	15,622	8,657
Accrued liabilities	1,552	1,073
Right of use asset	802	1,062
Stock-based compensation expense	6,386	1,909
Other, net	2
Total deferred tax assets	77,190	36,448
Deferred tax liabilities
Fixed assets	(124)	(154)
Lease liabilities	(705)	(944)
Deferred Tax Liabilities, Gross	(829)	(1,098)
Total	76,361	35,350
Less: valuation allowance	$ (76,361)	(35,350)
Net deferred tax assets		$ 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, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Beginning balance	$ 14,825	$ 7,488
(Reductions) for tax positions taken in prior years	(869)
Additions for tax positions taken in prior years		50
Additions for tax positions taken in current year	2,517	7,287
Ending balance	$ 16,473	$ 14,825

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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Loss from operations	$ (47,939)	$ (18,539)	$ (32,732)	$ (62,626)	$ (23,065)	$ (22,140)	$ (18,454)	$ (14,065)	$ (161,836)	$ (77,724)	$ (25,640)
Net loss	$ (47,376)	$ (17,705)	$ (31,493)	$ (60,718)	$ (20,959)	$ (20,483)	$ (17,142)	$ (13,547)	$ (157,292)	$ (72,131)	$ (24,785)
Net loss per share, basic and diluted	$ (1.02)	$ (0.42)	$ (0.82)	$ (1.69)	$ (0.58)	$ (0.63)	$ (0.70)	$ (3.97)	$ (3.85)	$ (2.99)	$ (7.31)
Weighted-average common shares outstanding, basic and diluted	46,588,835	42,185,824	38,603,236	35,919,358	35,851,252	32,312,814	24,479,767	3,413,760	40,843,782	24,124,924	3,388,586

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Zai TPX-0022 Agreement - Subsequent Event	Jan. 10, 2021USD ($)
Subsequent Event [Line Items]
Upfront cash payment received	$ 25,000,000
Maximum
Subsequent Event [Line Items]
Milestone payments eligible to receive	336,000,000
Development Milestones | Maximum
Subsequent Event [Line Items]
Milestone payments eligible to receive	121,000,000
Sales Milestones | Maximum
Subsequent Event [Line Items]
Milestone payments eligible to receive	$ 215,000,000