Mirati Therapeutics (MRTX) 10-Q 6 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 29, 2021
Cover [Abstract]
Entity Central Index Key	0001576263
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-35921
Entity Registrant Name	Mirati Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-2693615
Entity Address, Address Line One	3545 Cray Court,
Entity Address, City or Town	San Diego,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	(Zip Code)
City Area Code	858
Local Phone Number	332-3410
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MRTX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		51,439,928

Description of Business

Description of Business	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of BusinessMirati Therapeutics, Inc. ("Mirati" or the "Company") is a clinical-stage oncology company developing product candidates to address the genetic and immunological promoters of cancer. The Company was incorporated under the laws of the State of Delaware on April 29, 2013 as Mirati Therapeutics, Inc. and is located in San Diego, California. The Company has a wholly owned subsidiary in Canada, MethylGene, Inc. ("MethylGene"), and operates in one business segment, primarily in the United States. The Company's common stock has been listed on the Nasdaq Global Select Market since June 5, 2018 and was previously listed on the Nasdaq Capital Market since July 15, 2013, under the ticker symbol "MRTX."

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 329,503	$ 885,562
Short-term investments	957,660	504,544
Other current assets	16,347	13,537
Total current assets	1,303,510	1,403,643
Property and equipment, net	9,061	7,809
Long-term investment	11,676	15,629
Right-of-use asset	39,278	39,890
Other long-term assets	17,307	9,157
Total assets	1,380,832	1,476,128
Accounts Payable	19,602	18,117
Current liabilities
Accrued Liabilities	57,503	53,355
Total current liabilities	77,105	71,472
Lease liability	43,175	41,905
Other liabilities	1,139	1,962
Total liabilities	121,419	115,339
Commitments and contingencies (see Note 9)
Shareholders’ equity
Preferred stock, $0.001 par value; 10,000,000 shares authorized; none issued and outstanding at both March 31, 2021 and December 31, 2020	0	0
Common stock, $0.001 par value; 100,000,000 shares authorized; 51,375,786 and 50,439,069 issued and outstanding at March 31, 2021 and December 31, 2020, respectively	51	50
Additional paid-in capital	2,515,824	2,481,218
Accumulated other comprehensive income	9,456	9,759
Accumulated deficit	(1,265,918)	(1,130,238)
Total shareholders’ equity	1,259,413	1,360,789
Total liabilities and shareholders’ equity	$ 1,380,832	$ 1,476,128

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.001	$ 0.001
Preferred stock authorized (shares)	10,000,000	10,000,000
Preferred stock issued (shares)	0	0
Preferred stock outstanding (shares)	0	0
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Common stock authorized (shares)	100,000,000	100,000,000
Common stock issued (shares)	51,375,786	50,439,069
Common stock outstanding (shares)	51,375,786	50,439,069

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue
License and collaboration revenues	$ 0	$ 267
Total revenue	0	267
Expenses
Research and development	104,071	71,708
General and administrative	28,350	18,046
Total operating expenses	132,421	89,754
Loss from operations	(132,421)	(89,487)
Other (expense) income, net	(3,259)	2,832
Net loss	(135,680)	(86,655)
Unrealized loss on available-for-sale investments	(303)	(182)
Comprehensive loss	$ (135,983)	$ (86,837)
Basic and diluted net loss per share (USD per share)	$ (2.67)	$ (2.02)
Weighted average number of shares used in computing net loss per share, basic and diluted (shares)	50,779,364	42,886,691

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Balance at beginning of period (shares) at Dec. 31, 2019		39,517,329
Balance at beginning of period at Dec. 31, 2019	$ 382,295	$ 40	$ 1,144,667	$ 9,889	$ (772,301)
Increase (Decrease) in Stockholders' Equity
Net loss	(86,655)				(86,655)
Issuance of common stock, net of issuance costs (shares)		3,538,462
Issuance of common stock, net of issuance costs	323,977	$ 4	323,973
Share-based compensation expense	21,567		21,567
Issuance of common stock under equity incentive plans (shares)		496,521
Issuance of common stock under equity incentive plans	15,183		15,183
Proceeds from disgorgement of shareholders' short-swing profits	41		41
Unrealized loss on investments	(182)			(182)
Balance at end of period (shares) at Mar. 31, 2020		43,552,312
Balance at end of period at Mar. 31, 2020	$ 656,226	$ 44	1,505,431	9,707	(858,956)
Balance at beginning of period (shares) at Dec. 31, 2020	50,439,069	50,439,069
Balance at beginning of period at Dec. 31, 2020	$ 1,360,789	$ 50	2,481,218	9,759	(1,130,238)
Increase (Decrease) in Stockholders' Equity
Net loss	(135,680)				(135,680)
Share-based compensation expense	24,722		24,722
Issuance of common stock under equity incentive plans (shares)		312,903
Issuance of common stock under equity incentive plans	$ 9,885		9,885
Net exercise of warrants (shares)	623,814	623,814
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized loss on investments	$ (303)			(303)
Balance at end of period (shares) at Mar. 31, 2021	51,375,786	51,375,786
Balance at end of period at Mar. 31, 2021	$ 1,259,413	$ 51	$ 2,515,824	$ 9,456	$ (1,265,918)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net loss	$ (135,680)	$ (86,655)
Non-cash adjustments reconciling net loss to operating cash flows:
Change in fair value of long-term investment	3,953	0
Depreciation of property and equipment	294	126
Amortization of premium and accretion of discounts on investments	1,001	(520)
Share-based compensation expense	24,722	21,567
Changes in operating assets and liabilities:
Other current assets	(2,810)	(100)
Other long-term assets	(8,149)	(519)
Right-of-use asset	612	188
Lease liability	1,270	(198)
Accounts payable, accrued liabilities, and other liabilities	4,371	7,107
Cash flows used in operating activities	(110,416)	(59,004)
Investing activities:
Purchases of short-term investments	(621,661)	(230,384)
Sales and maturities of short-term investments	167,240	108,381
Purchases of property and equipment	(1,107)	(224)
Cash flows used in investing activities	(455,528)	(122,227)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	0	323,977
Proceeds from issuance of common stock under equity incentive plans	9,885	15,183
Proceeds from disgorgement of shareholders' short-swing profits	0	41
Cash flows provided by financing activities	9,885	339,201
(Decrease) increase in cash, cash equivalents and restricted cash	(556,059)	157,970
Cash, cash equivalents and restricted cash, beginning of period	886,182	46,856
Cash, cash equivalents and restricted cash, end of period	330,123	204,826
Reconciliation of cash, cash equivalents and restricted cash, end of period:
Total cash, cash equivalents and restricted cash	330,123	204,826
Supplemental disclosures of non-cash investing activities:
Purchases of property and equipment included within accounts payable and accrued liabilities	$ 439	$ 408

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The unaudited condensed consolidated financial statements contained in this Quarterly Report on Form 10-Q have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC") and, therefore, certain information and disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") have been omitted. In the opinion of management, the information reflects all adjustments necessary to make the results of operations for the interim periods a fair statement of such operations. All such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for the full year. The condensed consolidated balance sheet at December 31, 2020 has been derived from the audited consolidated financial statements at that date, but does not include all information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2020. Use of Estimates The preparation of the Company's unaudited condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Reported amounts and footnote disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. Estimates and assumptions are reviewed quarterly. Any revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected. Cash, Cash Equivalents and Short-term Investments Cash and cash equivalents consist of cash and highly liquid securities with original maturities at the date of acquisition of ninety days or less. Investments with an original maturity of more than ninety days are considered short-term investments and have been classified by management as available-for-sale. These investments 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. Such investments are carried at fair value, and the unrealized gains and losses are reported as a component of accumulated other comprehensive income in shareholders’ equity until realized. Realized gains and losses from the sale of available-for-sale securities, if any, are determined on a specific identification basis. Concentration of Credit Risk The Company invests its excess cash in accordance with its investment policy. The Company's investments are comprised primarily of commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. The Company mitigates credit risk by maintaining a diversified portfolio and limiting the amount of investment exposure as to institution, maturity and investment type. Financial instruments that potentially subject the Company to significant credit risk consist principally of cash equivalents and short-term investments. Revenue Recognition The Company recognizes revenue in connection with certain collaboration and license agreements in accordance with the guidance of Revenue From Contracts With Customers, Accounting Standards Codification ("ASC") Topic 606 ("Topic 606"). Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements the Company determines are within the scope of Topic 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Leases The Company determines if an arrangement is a lease at inception. Lease right-of-use assets represent the Company's right to use an underlying asset for the lease term and lease liabilities represent the Company's obligation to make lease payments arising from the lease. For operating leases with an initial term greater than 12 months, the Company recognizes operating lease right-of-use assets and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease right-of-use assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when the Company is reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For operating leases, if the interest rate used to determine the present value of future lease payments it not readily determinable, the Company estimates its incremental borrowing rate as the discount rate for the lease. The incremental borrowing rate is estimated to approximate the interest rate on a collateralized basis with similar terms and payments, and in similar economic environments. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has elected the practical expedient to not separate lease and non-lease components. Net Loss per Share Basic net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common share equivalents as they are anti-dilutive. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and common share equivalents outstanding for the period. Common share equivalents outstanding, determined using the treasury stock method, are comprised of shares that may be issued under the Company’s stock option and warrant agreements. The following table presents the weighted-average number of common share equivalents, calculated using the treasury stock method, not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Three months ended 2021 2020 Common stock options 2,758,415 2,174,353 Common stock warrants 8,043,004 9,692,771 Total 10,801,419 11,867,124 Recently Adopted and Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that are adopted by the Company as of the specified effective date. The Company has evaluated recently issued accounting pronouncements and does not believe any will have a material impact on the Company’s condensed consolidated financial statements or related financial statement disclosures.

Investments

Investments	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	Investments The following tables summarize the Company's short-term investments (in thousands): As of March 31, 2021 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 182,895 $ 45 $ (181) $ 182,759 Commercial paper 1 year or less 553,455 37 (19) 553,473 U.S. Agency bonds 2 years or less 133,484 48 — 133,532 U.S. Treasury bills 2 years or less 78,777 10 — 78,787 Sovereign debt securities 1 year or less 9,113 — (4) 9,109 $ 957,724 $ 140 $ (204) $ 957,660 As of December 31, 2020 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 130,814 $ 160 $ (4) $ 130,970 Commercial paper 1 year or less 240,725 58 (18) 240,765 U.S. Agency bonds 2 years or less 83,227 37 (1) 83,263 U.S. Treasury bills 2 years or less 49,539 10 (3) 49,546 $ 504,305 $ 265 $ (26) $ 504,544 The Company has classified all of its short-term investments as available-for-sale as the sale of such securities may be required prior to maturity to implement management strategies, and accordingly, carries these investments at fair value. As of March 31, 2021, and December 31, 2020, aggregated gross unrealized losses of available-for-sale investments were not material, and accordingly, no allowance for credit losses was recorded.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. The authoritative guidance for fair value measurements defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or the most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The guidance prioritizes the inputs used in measuring fair value into the following hierarchy: • Level 1- Quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2- Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable; and • Level 3- Unobservable inputs in which little or no market activity exists, therefore requiring an entity to develop its own assumptions about the assumptions that market participants would use in pricing. The following tables summarize the assets measured at fair value on a recurring basis (in thousands): March 31, 2021 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 34,614 $ 34,614 $ — $ — Money market funds 294,889 294,889 — — Total cash and cash equivalents 329,503 329,503 — — Short-term investments: U.S. Treasury bills 78,787 78,787 — — Corporate debt securities 182,759 — 182,759 — Commercial paper 553,473 — 553,473 — U.S. Agency bonds 133,532 — 133,532 — Sovereign debt securities 9,109 — 9,109 — Total short-term investments 957,660 78,787 878,873 — Long-term investment: ORIC Pharmaceuticals, Inc. 11,676 — — 11,676 Total $ 1,298,839 $ 408,290 $ 878,873 $ 11,676 December 31, 2020 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 20,398 $ 20,398 $ — $ — Money market funds 865,164 865,164 — — Total cash and cash equivalents 885,562 885,562 — — Short-term investments: U.S. Treasury bills 49,546 49,546 — — Corporate debt securities 130,970 — 130,970 — Commercial paper 240,765 — 240,765 — U.S. Agency bonds 83,263 — 83,263 — Total short-term investments 504,544 49,546 454,998 — Long-term investment: ORIC Pharmaceuticals, Inc. 15,629 — — 15,629 Total $ 1,405,735 $ 935,108 $ 454,998 $ 15,629 The Company’s investments in Level 1 assets are valued based on publicly available quoted market prices for identical securities as of March 31, 2021 and December 31, 2020. The Company determines the fair value of Level 2 related securities with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. As of March 31, 2021, the Level 3 fair value measurement of the Company's long-term investment in ORIC Pharmaceuticals, Inc., which was acquired in 2020, utilizes a combination of the Asian Protective Put Option and Finnerty Put Option fair value techniques with unobservable inputs of 96.0% volatility and an expected term of 0.8 years to determine the discount for lack of marketability of 19.0%. There were no transfers between fair value measurement levels during the three months ended March 31, 2021 or the year ended December 31, 2020. The following table presents the changes in estimated fair value of the Company's asset measured using significant unobservable inputs (Level 3) (in thousands): March 31, Balance - December 31, 2020 $ 15,629 Change in fair value (3,953) Balance - March 31, 2021 $ 11,676

Other Current Assets and Other

Other Current Assets and Other Long-Term Assets	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Current Assets and Other Long-Term Assets	Other Current Assets and Other Long-Term Assets Other current assets consisted of the following (in thousands): March 31, December 31, Prepaid expenses $ 9,933 $ 8,158 Deposits and other receivables 4,576 3,075 Interest receivable 1,838 2,304 $ 16,347 $ 13,537 The other long-term assets balance of $17.3 million as of March 31, 2021 consisted of $16.7 million in deposits paid in conjunction with the Company's research and development activities, and $0.6 million for a letter of credit secured by restricted cash in connection with the lease of the Company's corporate headquarters. The other long-term assets balance of $9.2 million as of December 31, 2020 consisted of $8.6 million in deposits paid in conjunction with the Company's research and development activities, and $0.6 million for a letter of credit secured by restricted cash in connection with the lease of the Company's corporate headquarters.

Accrued Liabilities and Other L

Accrued Liabilities and Other Liabilities	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Liabilities and Other Liabilities	Accrued Liabilities and Other Liabilities Accrued liabilities consisted of the following (in thousands): March 31, December 31, Accrued clinical expense 24,355 19,221 Accrued manufacturing expense 15,779 13,019 Accrued development expense 4,537 5,439 Accrued compensation and benefits 7,689 13,964 Other accrued expenses 5,143 1,712 $ 57,503 $ 53,355

License and Collaboration Agree

License and Collaboration Agreements	3 Months Ended
	Mar. 31, 2021
Research and Development [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements BeiGene Agreement Terms of Agreement On January 7, 2018, the Company and BeiGene Ltd, ("BeiGene") entered into a Collaboration and License Agreement (the “BeiGene Agreement”), pursuant to which the Company and BeiGene agreed to collaboratively develop sitravatinib in Asia (excluding Japan and certain other countries), Australia and New Zealand (the “Licensed Territory”). Under the BeiGene Agreement, the Company granted BeiGene an exclusive license to develop, manufacture and commercialize sitravatinib in the Licensed Territory, with the Company retaining exclusive rights for the development, manufacture and commercialization of sitravatinib outside the Licensed Territory. As consideration for the rights granted to BeiGene under the BeiGene Agreement, BeiGene paid the Company a non-refundable, non-creditable up-front fee of $10.0 million. BeiGene is also required to make milestone payments to the Company of up to an aggregate of $123.0 million upon the first achievement of specified clinical, regulatory and sales milestones. The BeiGene Agreement additionally provides that BeiGene is obligated to pay to the Company royalties at tiered percentage rates ranging from mid-single digits to twenty percent on annual net sales of licensed products in the Licensed Territory, subject to reduction under specified circumstances. The BeiGene Agreement also provides that the Company will supply BeiGene with sitravatinib for use in BeiGene’s development activities in the Licensed Territory. The BeiGene Agreement will terminate upon the expiration of the last royalty term for the licensed products, which is the latest of (i) the date of expiration of the last valid patent claim related to the licensed products under the BeiGene Agreement, (ii) 10 years after the first commercial sale of a licensed product and (iii) the expiration of any regulatory exclusivity as to a licensed product. BeiGene may terminate the BeiGene Agreement at any time by providing 60 days prior written notice to the Company. Either party may terminate the BeiGene Agreement upon a material breach by the other party that remains uncured following 60 days after the date of written notice of such breach or upon certain bankruptcy events. In addition, the Company may terminate the BeiGene Agreement upon written notice to BeiGene under specified circumstances if BeiGene challenges the licensed patent rights. Revenue Recognition The Company evaluated the BeiGene Agreement under Topic 606. At the time we entered into the BeiGene Agreement, the Company determined the transaction price was equal to the up-front fee of $10.0 million. The transaction price 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. As such, of the up-front fee, the Company allocated $9.5 million to the license to the Company's intellectual property, bundled with the associated know-how, and $0.5 million to the initial obligation to supply sitravatinib for clinical development in the Licensed Territory. Licenses of Intellectual Property. The license to the Company’s intellectual property, bundled with the associated know-how, represents a distinct performance obligation. The license and associated know-how was transferred to BeiGene during the three months ended March 31, 2018, therefore during 2018 the Company recognized the full revenue amount of $9.5 million related to this performance obligation as license and collaboration revenues in its condensed consolidated statements of operations and comprehensive loss. Manufacturing Supply Services. The Company's initial obligation to supply sitravatinib for clinical development in the Licensed Territory represents a distinct performance obligation, and the initial obligation was satisfied in 2020, therefore this $0.5 million initial supply obligation has been fully recognized in license and collaboration revenues as of December 31, 2020. Although the initial performance obligation was satisfied, BeiGene may request additional sitravatinib in the future for clinical development in the Licensed Territory. The Company recognizes revenue when BeiGene obtains control of the goods, upon delivery, over the period of the obligation. No revenue related to this performance obligation was recognized for the three months ended March 31, 2021. The Company recognized $0.3 million as license and collaboration revenues for this performance obligation for the three months ended March 31, 2020, primarily consisting of cost-sharing payments due from BeiGene. Milestone Payments. The Company is entitled to development milestones under the BeiGene Agreement. The next clinical development milestone is for BeiGene initiating the first pivotal clinical trial in the Licensed Territory upon which the Company will be paid a $5.0 million milestone payment. The Company is also entitled to certain regulatory milestone payments which are paid upon receipt of regulatory approvals within the Licensed Territory. No milestone payments were earned during the three months ended March 31, 2021 or 2020. The Company evaluated whether the remaining milestones are considered probable of being reached and determined that their achievement is highly dependent on factors outside of the Company's control. Therefore, these payments have been fully constrained and are not included in the transaction price. At the end of each subsequent reporting period, the Company will re-evaluate the probability of achievement of each milestone and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect the reported amount of license and collaboration revenues in the period of adjustment. Royalties. As the license is deemed to be the predominant item to which sales-based royalties relate, the Company will recognize revenue when the related sales occur. No royalty revenue was recognized during the three months ended March 31, 2021 or 2020. Pfizer Agreement In October 2014, the Company entered into a drug discovery collaboration and option agreement with Array BioPharma, Inc. ("Array," acquired by Pfizer Inc. ("Pfizer") during 2019) whereby Array provided services to facilitate the discovery, optimization and development of small molecule compounds that bind and specifically inhibit KRAS G12C. In June 2017, the two parties entered into a second, separate discovery collaboration and option agreement whereby Array provided services to facilitate the discovery, optimization and development of small molecule compounds that bind and specifically inhibit KRAS G12D. Both agreements established an option mechanism which enabled the Company to elect an exclusive worldwide license under the technology for the development and commercialization of certain products based on such compounds. Under the agreements, following the joint discovery periods which have concluded, the Company executed its options to retain exclusive worldwide licenses to develop, manufacture and commercialize inhibitors of KRAS G12C and KRAS G12D, including but not limited to, MRTX849 (adagrasib is the provisionally filed name for MRTX849) and MRTX1133. Under each agreement, Pfizer is entitled to potential development milestone payments of up to $9.3 million, and tiered sales milestone payments of up to $337.0 million based upon worldwide net sales, and tiered royalties in the high single digits to mid-teens on worldwide net sales of products arising from the collaborations. Under the agreements, the Company has incurred $4.5 million in development milestone payments from inception through March 31, 2021. The royalty term for each agreement shall be payable on a country-by-country and product-by-product basis, and separately will terminate at the later of (i) the date of expiration of the last valid patent claim within the collaboration patent rights or the Pfizer background technology covering such product in the country in which such product is sold at the time of such sale, or (ii) 10 years after the first commercial sale of such product in such country. The Company may terminate each agreement at any time by providing 60 days prior written notice to Pfizer. Either party may terminate each agreement upon a material breach by the other party that remains uncured following 60 days after the date of written notice of such breach or upon certain bankruptcy events. For the three months ended March 31, 2021, no expenses were incurred under these agreements with Pfizer. For the three months ended March 31, 2020, the Company incurred expenses of $4.5 million, consisting of a $3.0 million milestone payment for initiation of the first Phase 2 trial for MRTX849, and $1.5 million in research and development services. ORIC Pharmaceuticals Agreement Terms of Agreement On August 3, 2020, the Company entered into a license agreement with ORIC Pharmaceuticals, Inc. ("ORIC") pursuant to which the Company granted to ORIC an exclusive, worldwide license to develop and commercialize the Company's allosteric polycomb repressive complex 2 ("PRC2") inhibitors for all indications (the "ORIC License Agreement"). In accordance with the terms of the ORIC License Agreement, in exchange for such license, ORIC issued 588,235 shares of its common stock (the "Shares") to the Company on August 3, 2020. The Shares were issued under a stock issuance agreement entered into between ORIC and the Company, dated August 3, 2020. During the eighteen-month period following the date of the stock issuance agreement, the Company is subject to certain transfer restrictions. ORIC is not obligated to pay the Company milestone payments or royalty payments under the ORIC License Agreement. Unless terminated earlier, the ORIC License Agreement will continue in effect on a country-by-country and licensed product-by-licensed product basis until the later (a) the expiration of the last valid claim of a licensed patent covering such licensed product in such country or (b) ten years after the first commercial sale of such licensed product in such country. Following the expiration of the ORIC License Agreement, ORIC will retain its licenses under the intellectual property the Company licensed to ORIC on a royalty-free basis. The Company and ORIC may each terminate the ORIC License Agreement if the other party materially breaches the terms of such agreement, subject to specified notice and cure provisions, or enters into bankruptcy or insolvency proceedings. The Company may terminate the agreement if ORIC challenges any of the patent rights licensed to ORIC by the Company or if ORIC discontinues development of licensed products for a specified period of time. ORIC also has the right to terminate the ORIC License Agreement without cause by providing prior written notice to the Company. Revenue Recognition The Company accounted for the ORIC License Agreement under Topic 606 and identified the granting of an exclusive, worldwide license to develop and commercialize the Company's allosteric PRC2 inhibitors for all indications as a distinct performance obligation since ORIC can benefit from the license on its own by developing and commercializing the underlying product using its own resources. In determining the transaction price, the Company received the Shares as non-cash consideration. The Company allocated the entire transaction price to the distinct performance obligation described above, and the license and related know-how was transferred to ORIC during the third quarter of 2020. Therefore, the Company recognized the entire transaction price during 2020 and classified the amount as license and collaboration revenues in its condensed consolidated statements of operations and comprehensive loss. There were no such revenues recorded during the three months ended March 31, 2021. The Shares are carried at fair value and are recorded on the condensed consolidated balance sheet as a long-term investment. Any change in fair value is recorded within other (expense) income, net on the condensed consolidated statements of operations and comprehensive loss. The value of the long-term investment is determined by utilizing a Level 3 fair value measurement as further described in Note 4.

Warrants

Warrants	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Warrants	Warrants As of March 31, 2021, the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 3,578,036 November 20, 2017 None $ 0.001 3,669,360 June 11, 2018 None $ 0.001 358,415 7,605,811 During the three months ended March 31, 2021, 623,821 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 623,814 shares of common stock. No warrants were exercised during the three months ended March 31, 2020. Sale of Common Stock In October 2020, the Company sold 4,585,706 shares of its common stock at a public offering price of $202.00 per share. After deducting underwriter discounts, commissions and estimated offering expenses, the Company received net proceeds from the transaction of $879.6 million. In January 2020, the Company sold 3,538,462 shares of its common stock at a public offering price of $97.50 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net proceeds from the transaction of $324.0 million. At the Market Facility On July 2, 2020, the Company entered into a sales agreement pursuant to which the Company may, from time to time, sell shares of the Company's common stock, par value $0.001 per share, having an aggregate offering price of up to $200.0 million. As of March 31, 2021, the Company has not offered or sold any shares of common stock pursuant to this sales agreement. Share-based Compensation Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three months ended 2021 2020 Research and development expense $ 14,534 $ 11,848 General and administrative expense 10,188 9,719 $ 24,722 $ 21,567 During the three months ended March 31, 2021, 312,903 shares of common stock were issued under the Company's equity incentive plans, generating net proceeds of $9.9 million. During the three months ended March 31, 2020, 496,521 shares of common stock were issued under the Company's equity incentive plans, generating net proceeds of $15.2 million.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and ContingenciesOn June 30, 2020, the Company entered into an amended and restated lease agreement (the "Amended and Restated Lease") for office and laboratory space located in San Diego, California, for the Company's new corporate headquarters. The Amended and Restated Lease supersedes in its entirety the original lease agreement for the Company's future corporate headquarters dated as of August 22, 2019. The Amended and Restated Lease has a lease term of 12 years ("Lease Term"), unless terminated earlier. The Lease Term has an initial abatement period, and the initial base rent payable will be approximately $0.6 million per month following the abatement period, which amount will increase by 3% per year over the Lease Term. The Company has also received incentives from the landlord for tenant improvements. During 2020, the underlying asset was available for use by the Company to construct tenant improvements and therefore, the Lease Term was considered to have commenced. The Amended and Restated Lease is considered to be an operating lease, and the Amended and Restated Lease indicates the interest rate applicable to the lease is 12%, therefore the Company used a discount rate of 12% to calculate the value of its lease payments over the Lease Term. As of March 31, 2021, the condensed consolidated balance sheet includes an operating right-of-use asset of $39.3 million and an operating lease liability of $43.2 million. As of December 31, 2020, the consolidated balance sheet includes an operating right-of-use asset of $39.9 million and an operating lease liability of $41.9 million. For the three months ended March 31, 2021, the Company recorded $2.0 million in operating lease expense. As of March 31, 2021, the approximate future minimum lease payments under the Amended and Restated Lease are as follows (in thousands): Operating Lease 2021 - remainder $ — 2022 1,681 2023 7,844 2024 8,080 2025 8,322 Thereafter 68,257 Total operating lease payments (†) 94,184 Less: Amount representing interest (51,009) Total lease liability $ 43,175 ____________________ † The Company has an early termination right 7 years into the lease term, in which the total contractual obligation would be reduced by $41.1 million. On June 24, 2014, the Company entered into a lease agreement for completed office and laboratory space located in San Diego, California. The office space under the lease was the Company's corporate headquarters. The lease commenced in two phases (in July 2014 and March 2015) at a combined total initial monthly rent of $24,100 per month and was subject to a 3% annual rent increase following availability. In addition to such base monthly rent, the Company is obligated to pay certain customary amounts for its share of operating expenses and facility amenities. The original lease provided for expiration on January 31, 2018, and the Company entered into subsequent amendments to the original lease to extend the lease term to mid-2021. All other terms and covenants from the original lease agreement remain unchanged. For the three months ended March 31, 2020, the Company recorded $0.1 million in operating lease cost.

Shareholders' Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Shareholders' Equity	Warrants As of March 31, 2021, the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 3,578,036 November 20, 2017 None $ 0.001 3,669,360 June 11, 2018 None $ 0.001 358,415 7,605,811 During the three months ended March 31, 2021, 623,821 warrants for shares of the Company's common stock were exercised via cashless exercise, resulting in the issuance of 623,814 shares of common stock. No warrants were exercised during the three months ended March 31, 2020. Sale of Common Stock In October 2020, the Company sold 4,585,706 shares of its common stock at a public offering price of $202.00 per share. After deducting underwriter discounts, commissions and estimated offering expenses, the Company received net proceeds from the transaction of $879.6 million. In January 2020, the Company sold 3,538,462 shares of its common stock at a public offering price of $97.50 per share. After deducting underwriter discounts, commissions and offering expenses, the Company received net proceeds from the transaction of $324.0 million. At the Market Facility On July 2, 2020, the Company entered into a sales agreement pursuant to which the Company may, from time to time, sell shares of the Company's common stock, par value $0.001 per share, having an aggregate offering price of up to $200.0 million. As of March 31, 2021, the Company has not offered or sold any shares of common stock pursuant to this sales agreement. Share-based Compensation Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three months ended 2021 2020 Research and development expense $ 14,534 $ 11,848 General and administrative expense 10,188 9,719 $ 24,722 $ 21,567 During the three months ended March 31, 2021, 312,903 shares of common stock were issued under the Company's equity incentive plans, generating net proceeds of $9.9 million. During the three months ended March 31, 2020, 496,521 shares of common stock were issued under the Company's equity incentive plans, generating net proceeds of $15.2 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements contained in this Quarterly Report on Form 10-Q have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC") and, therefore, certain information and disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") have been omitted. In the opinion of management, the information reflects all adjustments necessary to make the results of operations for the interim periods a fair statement of such operations. All such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for the full year. The condensed consolidated balance sheet at December 31, 2020 has been derived from the audited consolidated financial statements at that date, but does not include all information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2020.
Use of Estimates	Use of Estimates The preparation of the Company's unaudited condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Reported amounts and footnote disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. Estimates and assumptions are reviewed quarterly. Any revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected.
Cash and Cash Equivalents	Cash and cash equivalents consist of cash and highly liquid securities with original maturities at the date of acquisition of ninety days or less.
Short-term Investments	Investments with an original maturity of more than ninety days are considered short-term investments and have been classified by management as available-for-sale. These investments 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.
Concentration of Credit Risk	Concentration of Credit Risk The Company invests its excess cash in accordance with its investment policy. The Company's investments are comprised primarily of commercial paper and debt instruments of financial institutions, corporations, U.S. government-sponsored agencies and the U.S. Treasury. The Company mitigates credit risk by maintaining a diversified portfolio and
Revenue Recognition	Revenue Recognition The Company recognizes revenue in connection with certain collaboration and license agreements in accordance with the guidance of Revenue From Contracts With Customers, Accounting Standards Codification ("ASC") Topic 606 ("Topic 606"). Under Topic 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements the Company determines are within the scope of Topic 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.
Leases	Leases The Company determines if an arrangement is a lease at inception. Lease right-of-use assets represent the Company's right to use an underlying asset for the lease term and lease liabilities represent the Company's obligation to make lease payments arising from the lease. For operating leases with an initial term greater than 12 months, the Company recognizes operating lease right-of-use assets and operating lease liabilities based on the present value of lease payments over the lease term at the commencement date. Operating lease right-of-use assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms include options to renew or terminate the lease when the Company is reasonably certain that the renewal option will be exercised or when it is reasonably certain that the termination option will not be exercised. For operating leases, if the interest rate used to determine the present value of future lease payments it not readily determinable, the Company estimates its incremental borrowing rate as the discount rate for the lease. The incremental borrowing rate is estimated to approximate the interest rate on a collateralized basis with similar terms and payments, and in similar economic environments. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company has elected the practical expedient to not separate lease and non-lease components.
Net Loss per Share	Net Loss per ShareBasic net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common share equivalents as they are anti-dilutive. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and common share equivalents outstanding for the period. Common share equivalents outstanding, determined using the treasury stock method, are comprised of shares that may be issued under the Company’s stock option and warrant agreements.
Recently Adopted and Recently Issued Accounting Pronouncements	Recently Adopted and Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that are adopted by the Company as of the specified effective date. The Company has evaluated recently issued accounting pronouncements and does not believe any will have a material impact on the Company’s condensed consolidated financial statements or related financial statement disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Schedule of Potentially Dilutive Securities not included in the Calculation of Diluted Net Loss per Share	The following table presents the weighted-average number of common share equivalents, calculated using the treasury stock method, not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Three months ended 2021 2020 Common stock options 2,758,415 2,174,353 Common stock warrants 8,043,004 9,692,771 Total 10,801,419 11,867,124

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Schedule of Short-Term Investments	The following tables summarize the Company's short-term investments (in thousands): As of March 31, 2021 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 182,895 $ 45 $ (181) $ 182,759 Commercial paper 1 year or less 553,455 37 (19) 553,473 U.S. Agency bonds 2 years or less 133,484 48 — 133,532 U.S. Treasury bills 2 years or less 78,777 10 — 78,787 Sovereign debt securities 1 year or less 9,113 — (4) 9,109 $ 957,724 $ 140 $ (204) $ 957,660 As of December 31, 2020 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 2 years or less $ 130,814 $ 160 $ (4) $ 130,970 Commercial paper 1 year or less 240,725 58 (18) 240,765 U.S. Agency bonds 2 years or less 83,227 37 (1) 83,263 U.S. Treasury bills 2 years or less 49,539 10 (3) 49,546 $ 504,305 $ 265 $ (26) $ 504,544

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize the assets measured at fair value on a recurring basis (in thousands): March 31, 2021 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 34,614 $ 34,614 $ — $ — Money market funds 294,889 294,889 — — Total cash and cash equivalents 329,503 329,503 — — Short-term investments: U.S. Treasury bills 78,787 78,787 — — Corporate debt securities 182,759 — 182,759 — Commercial paper 553,473 — 553,473 — U.S. Agency bonds 133,532 — 133,532 — Sovereign debt securities 9,109 — 9,109 — Total short-term investments 957,660 78,787 878,873 — Long-term investment: ORIC Pharmaceuticals, Inc. 11,676 — — 11,676 Total $ 1,298,839 $ 408,290 $ 878,873 $ 11,676 December 31, 2020 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 20,398 $ 20,398 $ — $ — Money market funds 865,164 865,164 — — Total cash and cash equivalents 885,562 885,562 — — Short-term investments: U.S. Treasury bills 49,546 49,546 — — Corporate debt securities 130,970 — 130,970 — Commercial paper 240,765 — 240,765 — U.S. Agency bonds 83,263 — 83,263 — Total short-term investments 504,544 49,546 454,998 — Long-term investment: ORIC Pharmaceuticals, Inc. 15,629 — — 15,629 Total $ 1,405,735 $ 935,108 $ 454,998 $ 15,629
Schedule of Changes in Estimated Fair Value of Assets with Unobservable Inputs	The following table presents the changes in estimated fair value of the Company's asset measured using significant unobservable inputs (Level 3) (in thousands): March 31, Balance - December 31, 2020 $ 15,629 Change in fair value (3,953) Balance - March 31, 2021 $ 11,676

Other Current Assets and Othe_2

Other Current Assets and Other Long-Term Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Current Assets	Other current assets consisted of the following (in thousands): March 31, December 31, Prepaid expenses $ 9,933 $ 8,158 Deposits and other receivables 4,576 3,075 Interest receivable 1,838 2,304 $ 16,347 $ 13,537

Accrued Liabilities and Other_2

Accrued Liabilities and Other Liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accounts Payable and Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): March 31, December 31, Accrued clinical expense 24,355 19,221 Accrued manufacturing expense 15,779 13,019 Accrued development expense 4,537 5,439 Accrued compensation and benefits 7,689 13,964 Other accrued expenses 5,143 1,712 $ 57,503 $ 53,355

Warrants (Tables)

Warrants (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of Warrants Issued and Outstanding	As of March 31, 2021, the following warrants for common stock were issued and outstanding: Issue date Expiration date Exercise price Number of warrants outstanding January 11, 2017 None $ 0.001 3,578,036 November 20, 2017 None $ 0.001 3,669,360 June 11, 2018 None $ 0.001 358,415 7,605,811

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments	As of March 31, 2021, the approximate future minimum lease payments under the Amended and Restated Lease are as follows (in thousands): Operating Lease 2021 - remainder $ — 2022 1,681 2023 7,844 2024 8,080 2025 8,322 Thereafter 68,257 Total operating lease payments (†) 94,184 Less: Amount representing interest (51,009) Total lease liability $ 43,175 ____________________ † The Company has an early termination right 7 years into the lease term, in which the total contractual obligation would be reduced by $41.1 million.

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Employee Service Share-based Compensation Allocation	Total share-based compensation expense by statement of operations and comprehensive loss classification is presented below (in thousands): Three months ended 2021 2020 Research and development expense $ 14,534 $ 11,848 General and administrative expense 10,188 9,719 $ 24,722 $ 21,567

Description of Business - Narra

Description of Business - Narrative (Details)	3 Months Ended
	Mar. 31, 2021segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended
	Mar. 31, 2021
Marketable Securities
Minimum original maturity period of marketable securities	90 days

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	10,801,419	11,867,124
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	2,758,415	2,174,353
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	8,043,004	9,692,771

Investments - Summary (Details)

Investments - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 957,724	$ 504,305
Gross unrealized gains	140	265
Gross unrealized losses	(204)	(26)
Estimated fair value	957,660	504,544
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	182,895	130,814
Gross unrealized gains	45	160
Gross unrealized losses	(181)	(4)
Estimated fair value	$ 182,759	$ 130,970
Corporate debt securities | Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 553,455	$ 240,725
Gross unrealized gains	37	58
Gross unrealized losses	(19)	(18)
Estimated fair value	$ 553,473	$ 240,765
Commercial paper | Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	1 year
U.S. Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 133,484	$ 83,227
Gross unrealized gains	48	37
Gross unrealized losses	0	(1)
Estimated fair value	$ 133,532	$ 83,263
U.S. Agency bonds | Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 78,777	$ 49,539
Gross unrealized gains	10	10
Gross unrealized losses	0	(3)
Estimated fair value	$ 78,787	$ 49,546
U.S. Treasury bills | Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Sovereign debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 9,113
Gross unrealized gains	0
Gross unrealized losses	(4)
Estimated fair value	$ 9,109
Sovereign debt securities | Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Schedule of Investments [Line Items]
Allowance for credit losses on available-for-sale investments	$ 0	$ 0
ORIC
Schedule of Investments [Line Items]
Stock held in investment (shares)	588,235	588,235

Fair Value Measurements - Summa

Fair Value Measurements - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 329,503	$ 885,562
Investments	957,660	504,544
Total	1,298,839	1,405,735
U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	78,787	49,546
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	182,759	130,970
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	553,473	240,765
U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	133,532	83,263
Sovereign debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	9,109
Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,676	15,629
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	34,614	20,398
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	294,889	865,164
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	329,503	885,562
Investments	78,787	49,546
Total	408,290	935,108
Level 1 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	78,787	49,546
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | Sovereign debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 1 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 1 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	34,614	20,398
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	294,889	865,164
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Investments	878,873	454,998
Total	878,873	454,998
Level 2 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	182,759	130,970
Level 2 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	553,473	240,765
Level 2 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	133,532	83,263
Level 2 | Sovereign debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	9,109
Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 2 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Investments	0	0
Total	11,676	15,629
Level 3 | U.S. Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 3 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 3 | U.S. Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Level 3 | Sovereign debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Level 3 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,676	15,629
Level 3 | Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	0	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash and cash equivalents	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details)	Mar. 31, 2021
Volatility
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	0.960
Expected Term
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	0.8
Discount for Lack of Marketability
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input of investment	0.190

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Estimated Fair Value of Assets with Unobservable Inputs (Details) - Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 15,629
Change in fair value	(3,953)
Balance at end of period	$ 11,676

Other Current Assets and Othe_3

Other Current Assets and Other Long-Term Assets - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 9,933	$ 8,158
Deposits and other receivables	4,576	3,075
Interest receivable	1,838	2,304
Other current assets	$ 16,347	$ 13,537

Other Current Assets and Othe_4

Other Current Assets and Other Long-Term Assets - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other long-term assets	$ 17,307	$ 9,157
Deposits paid for research and development	16,700	8,600
Security deposit for lease	$ 600	$ 600

Accrued Liabilities and Other_3

Accrued Liabilities and Other Liabilities - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued clinical expense	$ 24,355	$ 19,221
Accrued manufacturing expense	15,779	13,019
Accrued development expense	4,537	5,439
Accrued compensation and benefits	7,689	13,964
Other accrued expenses	5,143	1,712
Accrued liabilities	$ 57,503	$ 53,355

Accrued Liabilities and Other_4

Accrued Liabilities and Other Liabilities - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Other liabilities	$ 1,139	$ 1,962

License and Collaboration Agr_2

License and Collaboration Agreements - Narrative (Details) - USD ($)	Aug. 03, 2020	Jan. 07, 2018	Oct. 31, 2014	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement				$ 104,071,000	$ 71,708,000
BeiGene Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received		$ 10,000,000
Revenue from performance obligation expected to be earned		$ 123,000,000
Termination of contract, period after first commercial sale of product		10 years
Period required for notice of termination of contract		60 days
BeiGene Agreement | Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned						$ 9,500,000
BeiGene Agreement | Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned						$ 500,000
Payments received in advance				0	(300,000)
BeiGene Agreement | Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation expected to be earned				5,000,000
Milestone payments earned				0	0
BeiGene Agreement | Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue				0	0
Pfizer Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Termination of contract, period after first commercial sale of product			10 years
Period required for notice of termination of contract			60 days
Expenses related to collaboration agreement				$ 0	4,500,000
Pfizer Agreement | Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement					3,000,000
Pfizer Agreement | Research and Development Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement					$ 1,500,000
ORIC Pharmaceuticals Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock received as part of stock issuance and license agreements (shares)	588,235
License agreement, period of transfer restrictions	18 months
License agreement, period of agreement after first commercial sale	10 years

Warrants - Summary (Details)

Warrants - Summary (Details) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Class of Warrant or Right [Line Items]
Number of warrants outstanding (shares)	7,605,811
Warrants exercised via cashless exercises (shares)	623,821	0
Common stock issued from exercise of warrants (shares)	623,814
January 11, 2017 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001
Number of warrants outstanding (shares)	3,578,036
November 20, 2017 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001
Number of warrants outstanding (shares)	3,669,360
June 11, 2018 Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (USD per share)	$ 0.001
Number of warrants outstanding (shares)	358,415

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost		$ 100,000
Right-of-use asset	$ 39,278,000		$ 39,890,000
Current Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense	$ 2,000,000
Discount rate (as a percent)	12.00%
Right-of-use asset	$ 39,300,000		39,900,000
Operating lease liability	43,175,000		$ 41,900,000
Building | Current Headquarters
Lessee, Lease, Description [Line Items]
Minimum monthly rental expense	$ 24,100
Annual rent increase (as a percent)	3.00%
Building | Future Headquarters
Lessee, Lease, Description [Line Items]
Lease term	12 years
Minimum monthly rental expense	$ 600,000
Annual rent increase (as a percent)	3.00%

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments (Details) - Current Headquarters - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
2021 - remainder	$ 0
2022	1,681
2023	7,844
2024	8,080
2025	8,322
Thereafter	68,257
Total operating lease payments	94,184
Less: Amount representing interest	(51,009)
Total lease liability	$ 43,175	$ 41,900
Number of years into lease before termination can occur	7 years
Reduction of lease liability, amount	$ 41,100

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Oct. 31, 2020	Jan. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jul. 02, 2020
Share-based Payment Arrangement [Abstract]
Stock issued in transaction (shares)	4,585,706	3,538,462
Sale price of common stock (USD per share)	$ 202	$ 97.50
Proceeds from sale of stock	$ 879.6	$ 324
Common stock, par value (USD per share)			$ 0.001		$ 0.001	$ 0.001
Aggregate offering price						$ 200
Stock issued pursuant to stock option exercises (shares)			312,903	496,521
Proceeds from stock options exercised			$ 9.9	$ 15.2

Shareholders' Equity - Summary

Shareholders' Equity - Summary (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 24,722	$ 21,567
Research and development expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	14,534	11,848
General and administrative expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 10,188	$ 9,719

Uncategorized Items - mrtx-2021

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 321,000
Restricted Cash	us-gaap_RestrictedCash	620,000
Pfizer Discovery and Collaboration Agreement [Member] | Sales Milestone Payments [Member]
Research and Development Arrangement, Discovery and Collaboration Agreement, Compensation Expected to be Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementCompensationExpectedtobePaid	337,000,000
Pfizer Discovery and Collaboration Agreement [Member] | Development Milestone Payments [Member]
Research and Development Arrangement, Discovery and Collaboration Agreement, Compensation Expected to be Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementCompensationExpectedtobePaid	9,300,000
Research and Development Arrangement, Discovery and Collaboration Agreement, Milestone Payments Paid	mrtx_ResearchandDevelopmentArrangementDiscoveryandCollaborationAgreementMilestonePaymentsPaid	$ 4,500,000