Mirati Therapeutics (MRTX) 10-K 8 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 05, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	MIRATI THERAPEUTICS, INC.
Entity Central Index Key	1,576,263
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Entity Filer Category	Accelerated Filer
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Common Stock, Shares Outstanding		28,940,161
Entity Public Float			$ 74

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 107,703	$ 22,383
Short-term investments	43,134	34,351
Other current assets	4,922	2,821
Total current assets	155,759	59,555
Property and equipment, net	525	629
Other long-term assets	962	3,260
Total assets	157,246	63,444
Current liabilities
Accounts payable and accrued liabilities	13,644	15,002
Total current liabilities	13,644	15,002
Other liabilities	314	133
Total current liabilities	13,958	15,135
Stockholders' equity
Preferred stock, $0.001 par value, 10,000,000 shares authorized; none issued and outstanding at both December 31, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value; 100,000,000 authorized; 28,622,886 and 19,937,095 issued and outstanding at December 31, 2017 and December 31, 2016, respectively	29	20
Additional paid-in capital	594,407	428,507
Accumulated other comprehensive income	9,479	9,533
Accumulated deficit	(460,627)	(389,751)
Total stockholders' equity	143,288	48,309
Total liabilities and stockholders' equity	$ 157,246	$ 63,444

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	28,622,886	19,937,095
Common stock, shares outstanding	28,622,886	19,937,095

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expenses
Research and development	$ 58,085	$ 68,487	$ 48,959
General and administrative	13,450	15,292	15,755
Total operating expenses	71,535	83,779	64,714
Loss from operations	(71,535)	(83,779)	(64,714)
Other income, net	1,105	661	170
Net loss	(70,430)	(83,118)	(64,544)
Unrealized gain (loss) on available-for-sale investments	54	25	(37)
Comprehensive loss	$ (70,484)	$ (83,143)	$ (64,507)
Loss per share, basic (in US$ per share)	$ (2.78)	$ (4.20)	$ (3.82)
Weighted average number of shares used in computing net loss per share, basic and diluted (in shares)	25,290,222	19,787,349	16,901,826

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Beginning balance at Dec. 31, 2014	$ 28,062	$ 14	$ 260,616	$ 9,521	$ (242,089)
Beginning balance (in shares) at Dec. 31, 2014		13,566,726
Increase (Decrease) in Stockholders' Equity
Net loss	(64,544)				(64,544)
Stock-based compensation expense	10,254		10,254
Exercise of options for cash	552		552
Exercise of options for cash (in shares)		36,566
Issuance of common stock, net of costs	143,293	$ 4	143,289
Issuance of common stock, net of costs (in shares)		4,837,500
Issuance of common stock from ESPP	522		522
Issuance of common stock from ESPP purchase (in shares)		32,645
Net exercise of warrants	$ 0	$ 1	(1)
Net exercise of warrants (in shares)	809,498	809,498
Unrealized gain on investments	$ 37			37
Ending balance at Dec. 31, 2015	118,176	$ 19	415,232	9,558	(306,633)
Ending balance (in shares) at Dec. 31, 2015		19,282,935
Increase (Decrease) in Stockholders' Equity
Net loss	(83,118)				(83,118)
Stock-based compensation expense	10,624		10,624
Exercise of options for cash	240		240
Exercise of options for cash (in shares)		22,132
Issuance of common stock from ESPP	297		297
Issuance of common stock from ESPP purchase (in shares)		28,483
Net exercise of warrants	$ 0
Net exercise of warrants (in shares)	603,545	289,789
Exercise of warrants for cash	$ 2,115	$ 1	2,114
Exercise of warrants for cash (in shares)	313,756	313,756
Unrealized gain on investments	$ (25)			(25)
Ending balance at Dec. 31, 2016	$ 48,309	$ 20	428,507	9,533	(389,751)
Ending balance (in shares) at Dec. 31, 2016	19,937,095	19,937,095
Increase (Decrease) in Stockholders' Equity
Net loss	$ (70,430)				(70,430)
Stock-based compensation expense	6,786		6,786
Exercise of options for cash	$ 399		399
Exercise of options for cash (in shares)	45,573	45,573
Issuance of common stock, net of costs	$ 153,530	$ 8	153,522
Issuance of common stock, net of costs (in shares)		7,941,688
Issuance of common stock from ESPP	144		144
Issuance of common stock from ESPP purchase (in shares)		59,976
Net exercise of warrants	$ 0
Net exercise of warrants (in shares)	638,554	52,825
Exercise of warrants for cash	$ 4,604	$ 1	4,603
Exercise of warrants for cash (in shares)	585,729	585,729
Unrealized gain on investments	$ (54)			(54)
Ending balance at Dec. 31, 2017	$ 143,288	$ 29	594,407	$ 9,479	$ (460,627)
Ending balance (in shares) at Dec. 31, 2017	28,622,886	28,622,886
Increase (Decrease) in Stockholders' Equity
Cumulative effect of accounting change for the adoption of ASU 2016.09			$ 446

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (70,430)	$ (83,118)	$ (64,544)
Non-cash adjustments reconciling net loss to operating cash flows
Depreciation of property and equipment	184	180	212
Amortization of premium on investments	(266)	7	337
Share-based compensation expense	6,786	10,624	10,254
Changes in operating assets and liabilities
Other current assets	(3,409)	254	279
Other long-term assets	3,606	(1,259)	(1,675)
Accounts payable and accrued liabilities	(1,341)	5,196	4,370
Other current and long term liabilities	164	99	53
Cash flows used in operating activities	(64,706)	(68,017)	(50,714)
Investing activities:
Purchases of short-term investments	(100,558)	(70,269)	(104,954)
Sales and maturities of short-term investments	91,988	108,720	54,530
Purchases of property and equipment	(81)	(196)	(329)
Cash flows provided by (used in) investing activities	(8,651)	38,255	(50,753)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	153,530	0	143,293
Proceeds from exercise of common stock options and warrants	5,003	2,355	552
Proceeds from issuance under employee stock purchase plan	144	297	522
Cash flows provided by financing activities	158,677	2,652	144,367
Increase (decrease) in cash and cash equivalents	85,320	(27,110)	42,900
Cash and cash equivalents, beginning of year	22,383	49,493	6,593
Cash and cash equivalents, end of year	107,703	22,383	49,493
Net exercise of warrants	$ 0	$ 0	$ 0

DESCRIPTION OF BUSINESS

DESCRIPTION OF BUSINESS	12 Months Ended
	Dec. 31, 2017
DESCRIPTION OF BUSINESS
DESCRIPTION OF BUSINESS	Description of Business Mirati Therapeutics, Inc. ("Mirati" or the "Company") is a clinical-stage oncology company developing targeted drug products to address the genetic, epigenetic and immunological promoters of cancer. The Company's common stock has been listed on the NASDAQ Capital Market since July 15, 2013 under the ticker symbol "MRTX." The Company has a wholly owned subsidiary in Canada, MethylGene, Inc. ("MethylGene").

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Summary of Significant Accounting Policies Basis of Presentation These consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP"). These consolidated financial statements include the accounts of the Company and MethylGene. All significant inter-company transactions, balances and expenses have been eliminated upon consolidation. Mirati was incorporated under the laws of the State of Delaware on April 29, 2013. On May 8, 2013, the Company's Board of Directors approved and the Company entered into an arrangement agreement ("Arrangement") with MethylGene. Upon completion of the Arrangement, MethylGene became the Company's wholly-owned subsidiary. These consolidated financial statements are presented in United States ("U.S.") Dollars, which is also the functional currency of the Company. Use of Estimates The preparation of the Company's audited consolidated financial statements in conformity with U.S. GAAP 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 expenses during the reporting period. Reported amounts and note 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, with unrealized gains and losses included as a separate component of stockholders’ equity. Realized gains and losses from the sale of available-for-sale securities or the amounts, net of tax, reclassified out of accumulated other comprehensive income, 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. Property and Equipment, Net Property and equipment is stated at historical cost less accumulated depreciation. Historical cost includes expenditures that are directly attributable to the acquisition of the items. All repairs and maintenance are charged to net loss during the financial period in which they are incurred. Depreciation of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets, as follows: Computer equipment 3 years Office and other equipment 6 years Laboratory equipment 6 years Leasehold improvements The lesser of the lease term or the life of the asset Upon disposal or impairment of property and equipment, the cost and related accumulated depreciation is removed from the consolidated financial statements and the net amount, less any proceeds, is included in net loss. Impairment of Long-Lived Assets The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If such circumstances are determined to exist, an estimate of undiscounted future cash flows produced by the long-lived asset, including its eventual residual value, is compared to the carrying value to determine whether impairment exists. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. Fair value is estimated through discounted cash flow models to project cash flows from the asset. The Company recognized no impairment charges for the years ended December 31, 2017 , 2016 and 2015. Share-Based Compensation The Company measures and recognizes compensation expense for share-based payments based on estimated fair value, using the fair value of stock options granted using the Black-Scholes option-pricing model. The Black-Scholes option-pricing model requires the use of certain estimates and highly judgmental assumptions that affect the amount of share-based compensation expense recognized in the Company's consolidated financial statements. These assumptions include the historical volatility of the Company's stock price, expected term of the options, the risk-free interest rate and expected dividend yields. Share-based compensation is recognized using the graded accelerated vesting method. If any of the assumptions used in the Company's calculation change significantly, share-based compensation expense may differ materially from what the Company has recorded in the current period. Investment Tax Credits The Company's accounts include claims for investment tax credits ("ITCs") relating to scientific research and experimental development activities of the Company. The qualification and recording of these activities for investment tax credit purposes are established by the Canadian federal and Provincial Tax Acts and are subject to audit by the taxation authorities. Refundable ITCs are reflected as reductions of expenses or reductions of the cost of the assets to which they relate when there is reasonable assurance that the assistance will be received and all conditions have been complied with. The non-refundable ITCs are carried forward for a time and will be recognized when it is more likely than not that the Company will become subject to Canadian federal taxes, at which time, these ITCs will be applied as a reduction of tax expense. As operations in Canada ceased in early 2014, there were no new ITCs earned for the years ended December 31, 2017, 2016 or 2015. Research and Development Expenses Research and development expenditures are charged to net loss in the period in which they are incurred and are comprised of the following types of costs incurred in performing research and development activities: contract services for clinical trials and related clinical manufacturing costs, salaries and benefits including share-based compensation expense, costs for allocated facilities and depreciation of equipment and license fees paid in connection with our early discovery efforts. Income Taxes Income taxes have been accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net loss in the period that includes the enactment date. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. For uncertain tax positions that meet "a more likely than not" threshold, the Company recognizes the benefit of uncertain tax positions in the consolidated financial statements. Segment Reporting Operating segments are components of a business where separate discrete financial information is available for evaluation by the chief operating decision-maker for purposes of making decisions regarding resource allocation and assessing performance. To date, the Company and the chief operating decision-maker has viewed its operations and managed its business as one segment operating primarily in the United States. Net Loss per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities 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 potentially dilutive securities not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Year ended December 31, 2017 2016 2015 Common stock options 38,675 173,776 582,662 Common stock warrants 7,534,576 315,834 1,546,201 Total 7,573,251 489,610 2,128,863

RECENTLY ISSUED AND RECENTLY AD

RECENTLY ISSUED AND RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS AND RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS	Recently Issued and Recently Adopted 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. Recently Adopted Accounting Pronouncements In January 2017, the FASB issued ASU No. 2017-01, Clarifying the Definition of a Business, which clarifies and provides a more robust framework to use in determining when a set of assets and activities is a business. The amendments in this update should be applied prospectively on or after the effective date. This update is effective for annual periods beginning after December 15, 2017, and interim periods within those periods. Early adoption is permitted for acquisition or deconsolidation transactions occurring before the issuance date or effective date and only when the transactions have not been reported in issued financial statements. The Company early adopted this standard effective April 1, 2017 in connection with an immaterial collaboration agreement it entered into during the quarter. The adoption of this standard did not have a material effect on its consolidated financial statements. In March 2016, the FASB issued Accounting Standard Update ("ASU") 2016-09, Compensation-Stock Compensation (Topic 718). The new guidance changes the accounting and simplifies various aspects of the accounting for share-based payments to employees. The guidance allows for a policy election to account for forfeitures as they occur or based on an estimated number of awards that are expected to vest. ASU 2016-09 is effective for annual periods beginning after December 15, 2016, with early adoption permitted. Effective January 1, 2017, the Company adopted the provisions of ASU 2016-09. The impact of this adoption was limited to the accounting for forfeitures of certain stock based awards, which is adopted on a modified retrospective basis. Upon adoption, the Company will no longer estimate forfeitures and will instead account for forfeitures as they occur. This policy election was made to allow simplification of the accounting for share-based awards. The cumulative effect of adoption was an increase to both additional paid-in capital and accumulated deficit of $0.4 million . In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements-Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. Under the new guidance, management is required to assess an entity’s ability to continue as a going concern, and to provide related footnote disclosures in certain circumstances. The provisions of this ASU are effective for annual periods ending after December 15, 2016, and for annual and interim periods thereafter; early adoption is permitted. We adopted this guidance as of December 31, 2016 and the adoption did not require any additional disclosures in our consolidated financial statements for the year ended December 31, 2016 or for the current period. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which will replace numerous requirements in U.S. GAAP, including industry-specific requirements, and provide companies with a single revenue recognition model for recognizing revenue from contracts with customers. The core principle of the new standard is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In August 2015, the FASB approved a proposal to defer the effective date of the guidance until annual and interim reporting periods beginning after December 15, 2017. Although we currently do not have any revenue contracts in 2017, we early adopted this standard effective January 1, 2017 using the full retrospective method of adoption so that, in the event we enter into any revenue contracts, the contracts will be accounted for under the new guidance from inception of the contract. Recently Issued Accounting Pronouncements In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Non-controlling Interests with a Scope Exception. The ASU allows companies to exclude a down round feature when determining whether a financial instrument (or embedded conversion feature) is considered indexed to the entity’s own stock. As a result, financial instruments (or embedded conversion features) with down round features may no longer be required to be accounted classified as liabilities. A company will recognize the value of a down round feature only when it is triggered and the strike price has been adjusted downward. For equity-classified freestanding financial instruments, such as warrants, an entity will treat the value of the effect of the down round, when triggered, as a dividend and a reduction of income available to common shareholders in computing basic earnings per share. For convertible instruments with embedded conversion features containing down round provisions, entities will recognize the value of the down round as a beneficial conversion discount to be amortized to earnings. The guidance in ASU 2017-11 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, and the guidance is to be applied using a full or modified retrospective approach. The Company does not anticipate that the adoption of ASU 2017-11 will have a material impact on its consolidated financial statements unless a transaction occurs that would need to be evaluated under this guidance at which time the Company will assess the impact of this standard. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation, to provide clarity and reduce both 1) diversity in practice and 2) cost and complexity when applying the guidance in Topic 718 to a change in the terms or conditions of a share-based payment award. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting under Topic 718. The amendments in ASU 2017-09 are effective for fiscal and interim reporting periods in fiscal years beginning after December 15, 2017. Early adoption is permitted, including adoption in any interim period. The amendments in ASU 2017-09 should be applied prospectively to an award modified on or after the adoption date. The Company does not anticipate that the adoption of ASU 2017-09 will have a material impact on its consolidated financial statements unless a transaction occurs that would need to be evaluated under this guidance at which time the Company will assess the impact of this standard. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) in order to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under previous GAAP. ASU 2016-02 requires that a lessee should recognize a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term on the balance sheet. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 (including interim periods within those periods) using a modified retrospective approach and early adoption is permitted. The Company will adopt ASU 2016-02 in the first quarter of 2019. Although the Company is in the process of evaluating the impact of adoption of the ASU on its consolidated financial statements, the Company currently believes the most significant changes will be related to the recognition of new right-of-use assets and lease liabilities on the Company's balance sheet for real estate operating leases. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. The new guidance enhances the reporting model for financial instruments and includes amendments to address aspects of recognition, measurement, presentation and disclosure. The update to the standard is effective for public companies for interim and annual periods beginning after December 15, 2017. The Company does not believe the adoption of this standard will have a material impact on its financial position, results of operations or related financial statement disclosures.

INVESTMENTS

INVESTMENTS	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	Investments The following tables summarize our short-term investments (in thousands): As of December 31, 2017 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 24,264 $ — $ (23 ) $ 24,241 Commercial paper 1 year or less 18,912 — (19 ) 18,893 $ 43,176 $ — $ (42 ) $ 43,134 As of December 31, 2016 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 20,622 $ — $ (3 ) $ 20,619 Commercial paper 1 year or less 13,717 15 — 13,732 $ 34,339 $ 15 $ (3 ) $ 34,351 Unrealized gains and losses on available-for-sale securities are included as a component of comprehensive loss. At December 31, 2017 , the Company did not have any securities in material unrealized loss positions. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. The Company does not intend to sell any investments prior to recovery of their amortized cost basis for any investments in an unrealized loss position.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2017
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 table summarizes the assets and liabilities measured at fair value on a recurring basis (in thousands): December 31, 2017 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 1,026 $ 1,026 $ — $ — Money market funds 106,677 106,677 — — Total cash and cash equivalents 107,703 107,703 — — Short-term investments: Corporate debt securities 24,241 — 24,241 — Commercial paper 18,893 — 18,893 — Total short-term investments 43,134 — 43,134 — Total $ 150,837 $ 107,703 $ 43,134 $ — December 31, 2016 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 2,728 $ 2,728 $ — $ — Money market funds 19,655 19,655 — — Total cash and cash equivalents 22,383 22,383 — — Short-term investments: Corporate debt securities 20,619 — 20,619 — Commercial paper 13,732 — 13,732 — Total short-term investments 34,351 — 34,351 — Total $ 56,734 $ 22,383 $ 34,351 $ — The Company’s investments in Level 1 assets are valued based on publicly available quoted market prices for identical securities as of December 31, 2017 and 2016 . 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. There were no transfers between fair value measurement levels for the years ended December 31, 2017 and 2016 .

OTHER CURRENT ASSETS AND LONG-T

OTHER CURRENT ASSETS AND LONG-TERM ASSETS	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
OTHER CURRENT ASSETS AND LONG-TERM ASSETS	Other Current Assets and Other Long-Term Assets Other current assets consisted of the following (in thousands): December 31, 2017 2016 Prepaid expenses $ 3,085 $ 1,879 Deposits and other receivables 1,600 759 Interest receivables 237 183 $ 4,922 $ 2,821 The other long-term assets balance as of December 31, 2017 consists of $1.0 million in deposits paid in conjunction with the Company's research and development activities compared to $3.3 million as of December 31, 2016 .

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2017 2016 Computer equipment $ 329 $ 329 Office and other equipment 301 301 Laboratory equipment 643 563 Leasehold improvements 63 63 Gross property and equipment 1,336 1,256 Less: Accumulated depreciation (811 ) (627 ) Property and equipment, net $ 525 $ 629 The Company incurred depreciation expense of $0.2 million during the years ended December 31, 2017 , 2016 and 2015 , respectively.

ACCOUNTS PAYABLE AND ACCRUED LI

ACCOUNTS PAYABLE AND ACCRUED LIABILITIES	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
ACCOUNTS PAYABLE AND ACCRUED LIABILITIES	Accounts Payable and Accrued Liabilities Accounts payable and accrued liabilities consisted of the following (in thousands): December 31, 2017 2016 Accounts payable $ 4,344 $ 6,296 Accrued clinical, development and other expenses 6,256 5,743 Accrued compensation and benefits 3,021 2,923 Other current liabilities 23 40 $ 13,644 $ 15,002

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
STOCKHOLDERS' EQUITY	Stockholders' Equity Common Stock The following shares were reserved for future issuance: December 31, 2017 Common stock options outstanding and available for future grant 6,306,836 Warrants to purchase common stock 11,396,262 Employee Stock Purchase Plan 178,896 17,881,994 Sale of Common Stock In November 2017, the Company sold 2,938,986 shares of its common stock at a public offering price of $13.00 per share and sold warrants to purchase up to 4,137,999 shares of its common stock at a public offering price of $12.999 per warrant share. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $86.7 million . In January 2017, the Company sold 5,002,702 shares of its common stock at a public offering price of $5.60 per share and sold warrants to purchase up to 7,258,263 shares of its common stock at a public offering price of $5.599 per warrant share. After deducting underwriter discounts and offering expenses, the Company received net proceeds from the transaction of $66.8 million . In both cases, the public offering price for the warrants was equal to the public offering price of the common stock, less the $0.001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent, for certain holders, and 9.99 percent for other holders, following such exercise. Warrants As of December 31, 2017 , 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 7,258,263 November 20, 2017 None $ 0.001 4,137,999 11,396,262 During the year ended December 31, 2017 , warrants for 52,825 shares of the Company's common stock were exercised via cashless exercises and 585,729 shares were exercised for cash generating proceeds of $4.6 million resulting in the issuance of a total of 638,554 shares of common stock. During the year ended December 31, 2016 , warrants for 289,789 shares of the Company's common stock were exercised via cashless exercises and 313,756 shared were exercised for cash generating proceeds of $2.1 million resulting in the issuance of a total of 603,545 shares of common stock. During the year ended December 31, 2015, warrants for 1,037,330 shares of the Company's common stock were exercised via cashless exercises resulting in the issuance of a total of 809,498 shares of common stock.

SHARE-BASED COMPENSATION

SHARE-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED COMPENSATION	Share-Based Compensation Equity Incentive Plan The Company has in place a stock option plan (the "Stock Option Plan") for the benefit of employees, directors, officers and consultants of the Company. In May 2013 our Board of Directors adopted the 2013 Equity Incentive Plan (the "2013 Plan"). The 2013 Plan was approved by our stockholders in connection with the Arrangement. Our Board of Directors and stockholders approved an amendment to the 2013 Plan in 2017 to, among other things, increase the aggregate number of shares of common stock authorized for issuance under the 2013 Plan by 2.9 million shares. The 2013 Plan is a continuation of and successor to the Stock Option Plan and no further grants will be made under the Stock Option Plan. As of December 31, 2017 , there were approximately 3.0 million stock options available to be issued. To date, share-based compensation awards under either the Stock Option Plan or the 2013 Plan consist of incentive and non-qualified stock options. Stock options granted under each of the plans must have an exercise price equal to at least 100% of the fair market value of our common stock on the date of grant and generally vest over four years. The Stock Option Plan has contractual terms ranging from five to seven years and the 2013 Plan has contractual terms ranging from seven to ten years. The following table summarizes our stock option activity and related information for the year ended December 31, 2017 : Number of options Weighted average exercise price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (millions) Balance outstanding as of December 31, 2016 2,813,342 $ 16.57 Granted 970,226 $ 5.36 Exercised (45,573 ) $ 8.74 Canceled/forfeited (415,908 ) $ 14.47 Expired (17,906 ) $ 12.50 Balance outstanding as of December 31, 2017 3,304,181 $ 13.67 7.2 $ 21.0 Options exercisable at December 31, 2017 1,843,808 $ 16.28 6.1 $ 7.3 Options vested and expected to vest at December 31, 2017 3,304,181 $ 13.67 7.2 $ 21.0 The total intrinsic value of stock options exercised was $0.3 million , $0.3 million and $0.6 million for the years ended December 31, 2017, 2016, and 2015 , respectively. The Company received total cash of $0.4 million , $0.2 million and $0.6 million for the exercise of options for the years ended December 31, 2017 , 2016 and 2015 , respectively. The total fair value of options vested during the years ended December 31, 2017 , 2016 and 2015 was $10.6 million , $8.6 million and $6.5 million , respectively. Upon option exercise, the Company issues new shares of its common stock. Total share-based compensation expense by statement of operations classification is presented below (in thousands): Year ended December 31, 2017 2016 2015 Research and development expense $ 3,192 $ 5,461 $ 3,669 General and administrative expense 3,594 5,163 6,585 $ 6,786 $ 10,624 $ 10,254 For the years ended December 31, 2017 , 2016 and 2015 , no share-based compensation expense was capitalized and there were no recognized tax benefits associated with the share-based compensation charge. The fair value of options granted is estimated at the date of grant using the Black-Scholes option pricing model. The assumptions used for the specified reporting periods and the resulting estimates of weighted-average estimated fair value per share of options granted during those periods are as follows: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 2.1% 1.5% 1.5% Dividend yield —% —% —% Volatility factor 96.0% 101.7% 104.3% Expected term (in years) 6.0 6.0 6.0 Weighted average estimated fair value per share $4.17 $13.32 $19.44 Risk-Free Interest Rate - The risk-free interest rate is the rate for periods equal to the expected term of the stock option based on U.S. Treasury zero-coupon bonds. Dividend Yield - The dividend yield is based on the Company’s history and expectation of dividend payouts. The Company has not paid, and does not intend to pay dividends. Volatility Factor - The expected volatility assumption was determined by examining the historical volatility of the Company's stock. Expected Term - The expected term represents the weighted average period the stock options are expected to be outstanding. The Company uses the simplified method for estimating the expected term as provided by the Securities and Exchange Commission. The simplified method calculates the expected term as the average time-to-vesting and the contractual life of the options. The Company believes this methodology is appropriate given the Company's limited history as a U.S. public company. The total compensation cost not yet recognized as of December 31, 2017 related to non-vested option awards was $4.4 million which will be recognized over a weighted-average period of 1.2 years. 2013 Employee Stock Purchase Plan In May 2013, the Company's Board of Directors adopted the ESPP. The ESPP was approved by the Company's stockholders in connection with the Arrangement. In December 2014, the ESPP became effective and the first purchase period began. The ESPP permits eligible employees to make payroll deductions to purchase up to $25,000 of the Company’s common stock on regularly scheduled purchase dates at a discount. Offering periods under the ESPP are not more than six months in duration and shares are purchased at 85% of the lower of the closing price for the Company’s common stock on the first day of the offering period or the date of purchase. The ESPP initially authorized the issuance of 300,000 shares of the Company’s common stock pursuant to rights granted to employees for their payroll deductions. As of December 31, 2017 , 121,104 shares have been issued out of the plan.

EMPLOYEE BENEFIT PLAN

EMPLOYEE BENEFIT PLAN	12 Months Ended
	Dec. 31, 2017
Compensation and Retirement Disclosure [Abstract]
EMPLOYEE BENEFIT PLAN	Employee Benefit Plan The Company has a defined contribution 401(k) plan (the "Plan") for all employees. Employees are eligible to participate in the Plan if they are at least 21 years of age or older. Under the terms of the Plan, employees may make voluntary contributions as a percentage of compensation. The Company matches up to 4% of an employee's contributions, subject to a limit of $2,500 per year. Expense associated with the Company's matching contribution totaled $0.1 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	Income Taxes The Company had no federal income tax expense and immaterial state tax expense for the years ended December 31, 2017 , 2016 and 2015 . The differences between the effective income tax rate and the statutory tax rates during the years ended 2017 , 2016 and 2015 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Net loss before tax $ (70,430 ) $ (83,118 ) $ (64,544 ) Statutory combined U.S. federal and state tax rate 34.00 % 34.00 % 34.00 % Statutory federal and state taxes (23,946 ) (28,260 ) (21,945 ) Increase (decrease) in taxes recoverable resulting from: Effect of change in valuation allowance (4,154 ) 28,446 22,350 Non-deductible share-based compensation 695 1,247 923 Tax credits (2,563 ) (2,906 ) (2,430 ) Share issue costs - temporary difference — (78 ) (184 ) Write off of Methylgene US NOL 307 — — Differential in income tax rates of foreign subsidiary (169 ) 261 31 Change in tax rate 303 — — Tax Cuts and Jobs Act 28,569 — — Uncertain tax positions 646 3,921 1,961 Return to provision and other true-ups 368 (2,619 ) (899 ) Other differences (56 ) (12 ) 193 Income tax benefit $ — $ — $ — Deferred Tax The following table summarizes the significant components of our deferred tax assets (in thousands): December 31, 2017 2016 Deferred tax assets: Tangible and intangible depreciable assets $ 17,927 $ 990 Stock compensation 4,976 6,635 Provisions 611 853 Net operating loss carry forwards 44,598 66,489 Capital loss carryforward 83 51 Scientific research and experimental development expenditures 5,467 5,531 Research and development tax credits 7,016 4,266 Total gross deferred tax assets 80,678 84,815 Less valuation allowance (80,678 ) (84,815 ) Net deferred tax assets $ — $ — Total valuation allowance decreased by $4.1 million for the year ended December 31, 2017 . The Company has established a full valuation allowance against its deferred tax assets as of December 31, 2017 due to the uncertainty surrounding the realization of such assets as evidenced by the cumulative losses from operations through December 31, 2017 . For Canadian federal income tax purposes, the Company's Canadian federal scientific research and experimental development expenditures amounted to $19.9 million at December 31, 2017 , 2016 and 2015 and for provincial income tax purposes amounted to $21.6 million at December 31, 2017 , 2016 and 2015 . As operations in Canada ceased during 2014, no expenditures were incurred for the years ended December 31, 2017 , 2016 and 2015 . These expenditures are available to reduce future taxable income and have an unlimited carry forward period. Scientific research and development expenditures are subject to verification by the taxation authorities, and accordingly, these amounts may vary by a material amount. In addition, the Company has research and development tax credit carryforwards for U.S. federal and state income tax purposes as of December 31, 2017 of $7.2 million and $2.9 million , respectively. The federal credits will begin to expire in 2033 unless utilized and the state credits have an indefinite life. At December 31, 2017 , the Company's net operating loss carry forwards ("NOLs") for U.S. federal and state income taxes were $110.3 million and $77.3 million , respectively and the Company's NOLs for Canadian federal and provincial income tax purposes were $80.6 million and $79.9 million , respectively. The NOLs are available to offset future taxable income from both U.S. federal and state tax sources, as well as Canadian federal and provincial tax sources and the tax benefits of which have not been recognized in the consolidated financial statements. The NOLs expire as follows (in thousands): US Canada Federal State Federal Provincial Expires in: 2030 $ — $ — $ 5,907 $ 5,985 2031 — — 7,059 7,066 2032 — — 13,308 12,433 2033 2,225 2,232 18,623 19,385 2034 7,276 22,162 32,401 31,809 2035 53,359 52,950 1,084 1,084 2036 23,379 — 777 777 2037 24,044 — 1,408 1,408 $ 110,283 $ 77,344 $ 80,567 $ 79,947 The future utilization of the U.S. federal and state NOL carryforwards to offset future taxable income may be subject to an annual limitation as a result of ownership changes that may have occurred previously or may occur in the future. The Tax Reform Act of 1986 (the "1986 Act") limits a company's ability to utilize certain tax credit carryforwards and net operating loss carryforwards in the event of a cumulative change in ownership in excess of 50% as defined in the Act. During 2017, the Company completed a study to assess whether an ownership change, as identified by Section 382 of the 1986 Act, had occurred from the Company’s formation through December 31, 2017. Based upon the study, the Company determined an ownership change had occurred during 2017, causing the annual utilization of the NOL and credit carryforwards to be limited. The Company does not believe any of the NOL and credit carryforwards generated through December 31, 2017 would expire solely as a result of annual limitations on the utilization of those attributes. The Canadian Federal and Provincial Tax Acts maintain similar rules in the case of acquisition of control, which may limit the utilization of tax attributes. The Company files income tax returns in the U.S. (federal and state) and Canada (federal and provincial). The Company’s U.S. operations have not been audited for any open taxation years. The Company has experienced losses for U.S. tax purposes and therefore, the taxation authorities may review any loss year, if and when the losses are utilized. For Canadian tax purposes, the Company remains subject to federal and provincial audit for the December 31, 2013 and subsequent taxable years. Where taxation years remain open, the Company considers it reasonably possible that issues may be raised or tax positions agreed to with the taxation authorities, which may result in increases or decreases of the balance of non-refundable ITCs and NOLs. However, an estimate of such increases and decreases cannot be currently made. A reconciliation of the beginning and ending amounts of unrecognized tax positions are as follows (in thousands): Federal Provincial/State December 31, December 31, 2017 2016 2015 2017 2016 2015 Unrecognized tax positions, beginning of year $ 1,095 $ 509 $ 42 $ 7,333 $ 2,274 $ 18 Gross increase — current period tax positions 588 598 445 227 195 259 Gross decrease — prior period tax positions — (9 ) (4 ) (3 ) — (3 ) Gross increase — prior period tax positions 11 — 26 — 4,866 2,000 Expiration of statute of limitations (1 ) (3 ) — (1 ) (2 ) — Unrecognized tax positions, end of year $ 1,693 $ 1,095 $ 509 $ 7,556 $ 7,333 $ 2,274 If recognized, none of the unrecognized tax positions would impact the Company's income tax benefit or effective tax rate as long as the Company's deferred tax assets remain subject to a full valuation allowance. The Company does not expect any significant increases or decreases to the Company's unrecognized tax positions within the next 12 months. The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense. The Company had no accrual for interest or penalties on tax matters as of December 31, 2017 and 2016 and the Company had no ongoing tax audits as of December 31, 2017 . On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (the "2017 Act"). The 2017 Act amends the Internal Revenue Code to reduce tax rates and modify policies, credits, and deductions for individuals and businesses. For businesses, the Act reduces the corporate tax rate from a maximum of 35% to a flat 21% rate. The rate reduction is effective on January 1, 2018. The provisional amount related to the re-measurement of certain deferred tax assets, based on the rates at which they are expected to reverse in the future, was $28.6 million . Due to the Company's full valuation allowance position, there was no net impact on the Company's income tax provision for the year ended December 31, 2017 as the reduction in the deferred tax asset balance was fully offset by a corresponding decrease in the valuation allowance. In conjunction with the 2017 Act, the SEC staff issued Staff Accounting Bulletin No. 118 to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the 2017 Act. The Company has recognized the provisional tax impacts related to deemed repatriated earnings and the revaluation of deferred tax assets and liabilities at December 31, 2017. There was no net impact on the Company's consolidated financial statements for the year ended December 31, 2017 as the corresponding adjustment was made to the valuation allowance. The ultimate impact may differ from these provisional amounts, possibly materially, due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the 2017 Act.

INVESTMENT TAX CREDITS

INVESTMENT TAX CREDITS	12 Months Ended
	Dec. 31, 2017
INVESTMENT TAX CREDITS
INVESTMENT TAX CREDITS	Investment Tax Credits In prior years, the Company was entitled to claim Canadian federal and provincial ITCs for eligible scientific research and development expenditures. The Company recorded ITCs based on management's best estimates of the amount to be recovered and ITCs claimed are subject to audit by the taxation authorities and accordingly, may vary by a material amount. The Company has not recorded federal or provincial ITCs since the year ended December 31, 2013, as the primary operations of the Company were moved from Canada to San Diego, California in early 2014. The Company's non-refundable Canadian federal ITCs as of December 31, 2017 are $3.9 million and relate to scientific research and development expenditures, which may be utilized to reduce Canadian federal income taxes payable in future years. The benefits of the non-refundable Canadian federal ITCs have not been recognized in the financial statements and will be recorded as a reduction of tax expense when realized. The non-refundable investment tax credits expire as follows (in thousands): Federal ITC Expires in: 2030 $ 764 2031 1,000 2032 1,125 2033 1,018 $ 3,907

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	Commitments and Contingencies On June 24, 2014, the Company entered into a lease agreement for approximately 18,000 square feet of completed office and laboratory space located in San Diego, California. The office space under the lease is 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. The leased property is subject to a 3% annual rent increase following availability that results in the Company recording deferred rent over the term of the lease. 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. On March 23, 2017, the Company entered into a First Amendment to Lease Agreement to amend the original lease agreement and to extend the term of the original lease for one year through January 31, 2019. All other terms and covenants from the original lease agreement remain unchanged. Future minimum payments required under the lease are summarized as follows (in thousands): Year Ending December 31: 2018 $ 289 2019 26 Thereafter — Total minimum lease payments $ 315 Total lease expense for the years ended December 31, 2017 , 2016 and 2015 was $0.7 million , $0.8 million , and $0.6 million , respectively.

QUARTERLY FINANCIAL DATA

QUARTERLY FINANCIAL DATA	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	Selected Quarterly Financial Data (Unaudited) The following is a summary of the quarterly results of the Company for the years ended December 31, 2017 and 2016 (unaudited, in thousands, except for per share data): Three Months Ended Year Ended 3/31/17 6/30/17 9/30/17 12/31/17 December 31, 2017 Operating loss $ (18,090 ) $ (18,616 ) $ (16,601 ) $ (18,228 ) $ (71,535 ) Net loss (17,846 ) (18,339 ) (16,350 ) (17,895 ) (70,430 ) Per common share: Loss per share, basic and diluted (1) $ (0.73 ) $ (0.74 ) $ (0.65 ) $ (0.67 ) $ (2.78 ) Three Months Ended Year Ended 3/31/16 6/30/16 9/30/16 12/31/16 December 31, 2016 Operating loss $ (22,118 ) $ (22,227 ) $ (19,581 ) $ (19,853 ) $ (83,779 ) Net loss (21,914 ) (22,061 ) (19,421 ) (19,722 ) (83,118 ) Per common share: Loss per share, basic and diluted (1) $ (1.13 ) $ (1.11 ) $ (0.97 ) $ (0.99 ) $ (4.20 ) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Event On January 7, 2018, the Company and BeiGene, Ltd. (“BeiGene”) entered into a Collaboration and License Agreement (the “Agreement”), under 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”). BeiGene is considered a related party as the Company and BeiGene have a common investor. Under the Agreement, Mirati granted BeiGene an exclusive license to develop, manufacture and commercialize sitravatinib in the Licensed Territory, with Mirati retaining exclusive rights for the development, manufacturing and commercialization of sitravatinib outside the Licensed Territory. As consideration for the rights granted to BeiGene under the Agreement, BeiGene agreed to pay to Mirati an upfront fee of $10.0 million. BeiGene is also required to make milestone payments to Mirati of up to an aggregate of $123.0 million upon the first achievement of specified clinical, regulatory and sales milestones. The Agreement additionally provides that BeiGene is obligated to pay to Mirati 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 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 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 Agreement at any time by providing 60 days’ prior written notice to Mirati. Either party may terminate the 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, Mirati may terminate the Agreement upon written notice to BeiGene under specified circumstances if BeiGene challenges the licensed patent rights.

SUMMARY OF SIGNIFICANT ACCOUN23

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of presentation	Basis of Presentation These consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP"). These consolidated financial statements include the accounts of the Company and MethylGene. All significant inter-company transactions, balances and expenses have been eliminated upon consolidation. Mirati was incorporated under the laws of the State of Delaware on April 29, 2013. On May 8, 2013, the Company's Board of Directors approved and the Company entered into an arrangement agreement ("Arrangement") with MethylGene. Upon completion of the Arrangement, MethylGene became the Company's wholly-owned subsidiary. These consolidated financial statements are presented in United States ("U.S.") Dollars, which is also the functional currency of the Company.
Use of Estimates	Use of Estimates The preparation of the Company's audited consolidated financial statements in conformity with U.S. GAAP 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 expenses during the reporting period. Reported amounts and note 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, 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, with unrealized gains and losses included as a separate component of stockholders’ equity. Realized gains and losses from the sale of available-for-sale securities or the amounts, net of tax, reclassified out of accumulated other comprehensive income, if any, are determined on a specific identification basis.
Concentration of Credit Risk	Concentration of Credit Risk
Property and equipment	Property and Equipment, Net Property and equipment is stated at historical cost less accumulated depreciation. Historical cost includes expenditures that are directly attributable to the acquisition of the items. All repairs and maintenance are charged to net loss during the financial period in which they are incurred. Depreciation of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets, as follows: Computer equipment 3 years Office and other equipment 6 years Laboratory equipment 6 years Leasehold improvements The lesser of the lease term or the life of the asset Upon disposal or impairment of property and equipment, the cost and related accumulated depreciation is removed from the consolidated financial statements and the net amount, less any proceeds, is included in net loss.
Impairment of long-lived assets	Impairment of Long-Lived Assets The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If such circumstances are determined to exist, an estimate of undiscounted future cash flows produced by the long-lived asset, including its eventual residual value, is compared to the carrying value to determine whether impairment exists. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. Fair value is estimated through discounted cash flow models to project cash flows from the asset.
Share-based compensation	Share-Based Compensation The Company measures and recognizes compensation expense for share-based payments based on estimated fair value, using the fair value of stock options granted using the Black-Scholes option-pricing model. The Black-Scholes option-pricing model requires the use of certain estimates and highly judgmental assumptions that affect the amount of share-based compensation expense recognized in the Company's consolidated financial statements. These assumptions include the historical volatility of the Company's stock price, expected term of the options, the risk-free interest rate and expected dividend yields. Share-based compensation is recognized using the graded accelerated vesting method. If any of the assumptions used in the Company's calculation change significantly, share-based compensation expense may differ materially from what the Company has recorded in the current period.
Investment tax credits	Investment Tax Credits The Company's accounts include claims for investment tax credits ("ITCs") relating to scientific research and experimental development activities of the Company. The qualification and recording of these activities for investment tax credit purposes are established by the Canadian federal and Provincial Tax Acts and are subject to audit by the taxation authorities. Refundable ITCs are reflected as reductions of expenses or reductions of the cost of the assets to which they relate when there is reasonable assurance that the assistance will be received and all conditions have been complied with. The non-refundable ITCs are carried forward for a time and will be recognized when it is more likely than not that the Company will become subject to Canadian federal taxes, at which time, these ITCs will be applied as a reduction of tax expense. As operations in Canada ceased in early 2014, there were no new ITCs earned for the years ended December 31, 2017, 2016 or 2015.
Research and development expenses	Research and Development Expenses Research and development expenditures are charged to net loss in the period in which they are incurred and are comprised of the following types of costs incurred in performing research and development activities: contract services for clinical trials and related clinical manufacturing costs, salaries and benefits including share-based compensation expense, costs for allocated facilities and depreciation of equipment and license fees paid in connection with our early discovery efforts
Income taxes	Income Taxes Income taxes have been accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net loss in the period that includes the enactment date. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. For uncertain tax positions that meet "a more likely than not" threshold, the Company recognizes the benefit of uncertain tax positions in the consolidated financial statements.
Segment Reporting	Segment Reporting Operating segments are components of a business where separate discrete financial information is available for evaluation by the chief operating decision-maker for purposes of making decisions regarding resource allocation and assessing performance. To date, the Company and the chief operating decision-maker has viewed its operations and managed its business as one segment operating primarily in the United States.
Net loss per share	Net Loss per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities 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.
Fair value measurement	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.

SUMMARY OF SIGNIFICANT ACCOUN24

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of estimated useful lives of assets	Depreciation of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets, as follows: Computer equipment 3 years Office and other equipment 6 years Laboratory equipment 6 years Leasehold improvements The lesser of the lease term or the life of the asset
Schedule of potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive	The following table presents the weighted average number of potentially dilutive securities not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities: Year ended December 31, 2017 2016 2015 Common stock options 38,675 173,776 582,662 Common stock warrants 7,534,576 315,834 1,546,201 Total 7,573,251 489,610 2,128,863

INVESTMENTS (Tables)

INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale and Trading Securities Reconciliation	The following tables summarize our short-term investments (in thousands): As of December 31, 2017 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 24,264 $ — $ (23 ) $ 24,241 Commercial paper 1 year or less 18,912 — (19 ) 18,893 $ 43,176 $ — $ (42 ) $ 43,134 As of December 31, 2016 Maturity Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value Corporate debt securities 1 year or less $ 20,622 $ — $ (3 ) $ 20,619 Commercial paper 1 year or less 13,717 15 — 13,732 $ 34,339 $ 15 $ (3 ) $ 34,351

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	The following table summarizes the assets and liabilities measured at fair value on a recurring basis (in thousands): December 31, 2017 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 1,026 $ 1,026 $ — $ — Money market funds 106,677 106,677 — — Total cash and cash equivalents 107,703 107,703 — — Short-term investments: Corporate debt securities 24,241 — 24,241 — Commercial paper 18,893 — 18,893 — Total short-term investments 43,134 — 43,134 — Total $ 150,837 $ 107,703 $ 43,134 $ — December 31, 2016 Total Level 1 Level 2 Level 3 Assets Cash and cash equivalents: Cash $ 2,728 $ 2,728 $ — $ — Money market funds 19,655 19,655 — — Total cash and cash equivalents 22,383 22,383 — — Short-term investments: Corporate debt securities 20,619 — 20,619 — Commercial paper 13,732 — 13,732 — Total short-term investments 34,351 — 34,351 — Total $ 56,734 $ 22,383 $ 34,351 $ —

OTHER CURRENT ASSETS AND LONG27

OTHER CURRENT ASSETS AND LONG-TERM ASSETS (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of other current assets	Other current assets consisted of the following (in thousands): December 31, 2017 2016 Prepaid expenses $ 3,085 $ 1,879 Deposits and other receivables 1,600 759 Interest receivables 237 183 $ 4,922 $ 2,821

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of property and equipment	Property and equipment, net consisted of the following (in thousands): December 31, 2017 2016 Computer equipment $ 329 $ 329 Office and other equipment 301 301 Laboratory equipment 643 563 Leasehold improvements 63 63 Gross property and equipment 1,336 1,256 Less: Accumulated depreciation (811 ) (627 ) Property and equipment, net $ 525 $ 629

ACCOUNTS PAYABLE AND ACCRUED 29

ACCOUNTS PAYABLE AND ACCRUED LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of accounts payable and accrued liabilities	Accounts payable and accrued liabilities consisted of the following (in thousands): December 31, 2017 2016 Accounts payable $ 4,344 $ 6,296 Accrued clinical, development and other expenses 6,256 5,743 Accrued compensation and benefits 3,021 2,923 Other current liabilities 23 40 $ 13,644 $ 15,002

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Schedule of Shares Reserved for Future Issuance	The following shares were reserved for future issuance: December 31, 2017 Common stock options outstanding and available for future grant 6,306,836 Warrants to purchase common stock 11,396,262 Employee Stock Purchase Plan 178,896 17,881,994
Schedule of warrants issued and outstanding	As of December 31, 2017 , 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 7,258,263 November 20, 2017 None $ 0.001 4,137,999 11,396,262

SHARE-BASED COMPENSATION (Table

SHARE-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of changes to the number of stock options granted by the Company and their weighted average exercise price	The following table summarizes our stock option activity and related information for the year ended December 31, 2017 : Number of options Weighted average exercise price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (millions) Balance outstanding as of December 31, 2016 2,813,342 $ 16.57 Granted 970,226 $ 5.36 Exercised (45,573 ) $ 8.74 Canceled/forfeited (415,908 ) $ 14.47 Expired (17,906 ) $ 12.50 Balance outstanding as of December 31, 2017 3,304,181 $ 13.67 7.2 $ 21.0 Options exercisable at December 31, 2017 1,843,808 $ 16.28 6.1 $ 7.3 Options vested and expected to vest at December 31, 2017 3,304,181 $ 13.67 7.2 $ 21.0
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	Total share-based compensation expense by statement of operations classification is presented below (in thousands): Year ended December 31, 2017 2016 2015 Research and development expense $ 3,192 $ 5,461 $ 3,669 General and administrative expense 3,594 5,163 6,585 $ 6,786 $ 10,624 $ 10,254
Schedule of assumptions used to estimate the fair value of options granted at the date of grant using the Black-Scholes option pricing model	The assumptions used for the specified reporting periods and the resulting estimates of weighted-average estimated fair value per share of options granted during those periods are as follows: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 2.1% 1.5% 1.5% Dividend yield —% —% —% Volatility factor 96.0% 101.7% 104.3% Expected term (in years) 6.0 6.0 6.0 Weighted average estimated fair value per share $4.17 $13.32 $19.44

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Reconciliation	The differences between the effective income tax rate and the statutory tax rates during the years ended 2017 , 2016 and 2015 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Net loss before tax $ (70,430 ) $ (83,118 ) $ (64,544 ) Statutory combined U.S. federal and state tax rate 34.00 % 34.00 % 34.00 % Statutory federal and state taxes (23,946 ) (28,260 ) (21,945 ) Increase (decrease) in taxes recoverable resulting from: Effect of change in valuation allowance (4,154 ) 28,446 22,350 Non-deductible share-based compensation 695 1,247 923 Tax credits (2,563 ) (2,906 ) (2,430 ) Share issue costs - temporary difference — (78 ) (184 ) Write off of Methylgene US NOL 307 — — Differential in income tax rates of foreign subsidiary (169 ) 261 31 Change in tax rate 303 — — Tax Cuts and Jobs Act 28,569 — — Uncertain tax positions 646 3,921 1,961 Return to provision and other true-ups 368 (2,619 ) (899 ) Other differences (56 ) (12 ) 193 Income tax benefit $ — $ — $ —
Schedule of deferred tax	The following table summarizes the significant components of our deferred tax assets (in thousands): December 31, 2017 2016 Deferred tax assets: Tangible and intangible depreciable assets $ 17,927 $ 990 Stock compensation 4,976 6,635 Provisions 611 853 Net operating loss carry forwards 44,598 66,489 Capital loss carryforward 83 51 Scientific research and experimental development expenditures 5,467 5,531 Research and development tax credits 7,016 4,266 Total gross deferred tax assets 80,678 84,815 Less valuation allowance (80,678 ) (84,815 ) Net deferred tax assets $ — $ —
Schedule of expiration of NOLs	The NOLs expire as follows (in thousands): US Canada Federal State Federal Provincial Expires in: 2030 $ — $ — $ 5,907 $ 5,985 2031 — — 7,059 7,066 2032 — — 13,308 12,433 2033 2,225 2,232 18,623 19,385 2034 7,276 22,162 32,401 31,809 2035 53,359 52,950 1,084 1,084 2036 23,379 — 777 777 2037 24,044 — 1,408 1,408 $ 110,283 $ 77,344 $ 80,567 $ 79,947
Schedule of reconciliation of the beginning and ending gross amounts of unrecognized tax positions	A reconciliation of the beginning and ending amounts of unrecognized tax positions are as follows (in thousands): Federal Provincial/State December 31, December 31, 2017 2016 2015 2017 2016 2015 Unrecognized tax positions, beginning of year $ 1,095 $ 509 $ 42 $ 7,333 $ 2,274 $ 18 Gross increase — current period tax positions 588 598 445 227 195 259 Gross decrease — prior period tax positions — (9 ) (4 ) (3 ) — (3 ) Gross increase — prior period tax positions 11 — 26 — 4,866 2,000 Expiration of statute of limitations (1 ) (3 ) — (1 ) (2 ) — Unrecognized tax positions, end of year $ 1,693 $ 1,095 $ 509 $ 7,556 $ 7,333 $ 2,274

INVESTMENT TAX CREDITS (Tables)

INVESTMENT TAX CREDITS (Tables)	12 Months Ended
	Dec. 31, 2017
INVESTMENT TAX CREDITS
Schedule of non-refundable investment tax credits expiration	The non-refundable investment tax credits expire as follows (in thousands): Federal ITC Expires in: 2030 $ 764 2031 1,000 2032 1,125 2033 1,018 $ 3,907

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum annual payment required in the next year	Future minimum payments required under the lease are summarized as follows (in thousands): Year Ending December 31: 2018 $ 289 2019 26 Thereafter — Total minimum lease payments $ 315

QUARTERLY FINANCIAL DATA (Table

QUARTERLY FINANCIAL DATA (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data	The following is a summary of the quarterly results of the Company for the years ended December 31, 2017 and 2016 (unaudited, in thousands, except for per share data): Three Months Ended Year Ended 3/31/17 6/30/17 9/30/17 12/31/17 December 31, 2017 Operating loss $ (18,090 ) $ (18,616 ) $ (16,601 ) $ (18,228 ) $ (71,535 ) Net loss (17,846 ) (18,339 ) (16,350 ) (17,895 ) (70,430 ) Per common share: Loss per share, basic and diluted (1) $ (0.73 ) $ (0.74 ) $ (0.65 ) $ (0.67 ) $ (2.78 ) Three Months Ended Year Ended 3/31/16 6/30/16 9/30/16 12/31/16 December 31, 2016 Operating loss $ (22,118 ) $ (22,227 ) $ (19,581 ) $ (19,853 ) $ (83,779 ) Net loss (21,914 ) (22,061 ) (19,421 ) (19,722 ) (83,118 ) Per common share: Loss per share, basic and diluted (1) $ (1.13 ) $ (1.11 ) $ (0.97 ) $ (0.99 ) $ (4.20 ) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

SUMMARY OF SIGNIFICANT ACCOUN36

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2017
Computer equipment
Property and equipment
Estimated useful lives	3 years
Office and other equipment
Property and equipment
Estimated useful lives	6 years
Laboratory equipment
Property and equipment
Estimated useful lives	6 years

SUMMARY OF SIGNIFICANT ACCOUN37

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Asset Impairment Charges	$ 0	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOUN38

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3) - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share (in shares)	2,128,863	7,573,251	489,610
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share (in shares)	582,662	38,675	173,776
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in the calculation of diluted net loss per share (in shares)	1,546,201	7,534,576	315,834

RECENTLY ISSUED AND RECENTLY 39

RECENTLY ISSUED AND RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS RECENTLY ISSUED AND RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jan. 01, 2017
Additional paid-in capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for the adoption of ASU 2016.09	$ 446
Accounting Standards Update 2016-09 [Member] | Additional paid-in capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for the adoption of ASU 2016.09		$ 400
Accounting Standards Update 2016-09 [Member] | Accumulated deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for the adoption of ASU 2016.09	$ 400

INVESTMENTS (Details)

INVESTMENTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized cost	$ 43,176	$ 34,339
Available-for-Sale, Gross unrealized gains	0	15
Available-for-Sale, Gross unrealized losses	(42)	(3)
Available-for-Sale, Estimated fair value	$ 43,134	$ 34,351
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, maximum maturity period	1 year	1 year
Available-for-Sale, Amortized cost	$ 24,264	$ 20,622
Available-for-Sale, Gross unrealized gains	0	0
Available-for-Sale, Gross unrealized losses	(23)	(3)
Available-for-Sale, Estimated fair value	$ 24,241	$ 20,619
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, maximum maturity period	1 year	1 year
Available-for-Sale, Amortized cost	$ 18,912	$ 13,717
Available-for-Sale, Gross unrealized gains	0	15
Available-for-Sale, Gross unrealized losses	(19)	0
Available-for-Sale, Estimated fair value	$ 18,893	$ 13,732

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Recurring basis - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 107,703	$ 22,383
Short-term investments	43,134	34,351
Assets, Fair Value Disclosure, Recurring	150,837	56,734
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	107,703	22,383
Assets, Fair Value Disclosure, Recurring	107,703	22,383
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Short-term investments	43,134	34,351
Assets, Fair Value Disclosure, Recurring	43,134	34,351
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	24,241	20,619
Corporate debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	24,241	20,619
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	18,893	13,732
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	18,893	13,732
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	1,026	2,728
Cash | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	1,026	2,728
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	106,677	19,655
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 106,677	$ 19,655

OTHER CURRENT ASSETS AND LONG42

OTHER CURRENT ASSETS AND LONG-TERM ASSETS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 3,085	$ 1,879
Deposits and other receivables	1,600	759
Interest receivables	237	183
Other current assets	4,922	2,821
Other Assets, Noncurrent [Abstract]
Deposits paid for research and development	$ 1,000	$ 3,300

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and equipment
Property and equipment, gross	$ 1,336	$ 1,256
Less: Accumulated depreciation	(811)	(627)
Property and equipment, net	525	629
Depreciation expenses	184	180	$ 212
Computer equipment
Property and equipment
Property and equipment, gross	329	329
Office and other equipment
Property and equipment
Property and equipment, gross	301	301
Laboratory equipment
Property and equipment
Property and equipment, gross	643	563
Leasehold improvements
Property and equipment
Property and equipment, gross	$ 63	$ 63

ACCOUNTS PAYABLE AND ACCRUED 44

ACCOUNTS PAYABLE AND ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accounts payable	$ 4,344	$ 6,296
Accrued clinical, development and other expenses	6,256	5,743
Accrued compensation and benefits	3,021	2,923
Other current liabilities	23	40
Total accounts payable and accrued liabilities	$ 13,644	$ 15,002

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details)	Dec. 31, 2017shares
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	17,881,994
Warrants to purchase common stock
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	11,396,262
Stock Option Plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	6,306,836
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	178,896

STOCKHOLDERS' EQUITY (Details 2

STOCKHOLDERS' EQUITY (Details 2) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Nov. 30, 2017	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 21, 2012
Warrants - issued and outstanding
Exercise of warrants for cash (in shares)			585,729	313,756
Proceeds from issuance of common stock, net of issuance costs	$ 86.7	$ 66.8	$ 4.6	$ 2.1
Exercise price (in dollars per share)	$ 12.999	$ 5.599	$ 0.001
Number of warrants (in shares)	4,137,999	7,258,263	11,396,262
Number of warrants exercised (in shares)			52,825	289,789	1,037,330
Net exercise of warrants (in shares)			638,554	603,545	809,498
Common Stock
Warrants - issued and outstanding
Issuance of common stock, net of costs (in shares)	2,938,986	5,002,702	7,941,688		4,837,500
Share Price	$ 13	$ 5.60
Exercise of warrants for cash (in shares)			585,729	313,756
Net exercise of warrants (in shares)			52,825	289,789	809,498
Private Placement | January 11, 2017 Warrants
Warrants - issued and outstanding
Exercise price (in dollars per share)			$ 0.001
Number of warrants (in shares)			7,258,263
Private Placement | November 20, 2017 Warrants
Warrants - issued and outstanding
Exercise price (in dollars per share)						$ 0.001
Certain Holders
Warrants - issued and outstanding
Common stock, ownership percent, threshold			19.99%
Other Holders
Warrants - issued and outstanding
Common stock, ownership percent, threshold			9.99%

SHARE-BASED COMPENSATION (Detai

SHARE-BASED COMPENSATION (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options available for issue	3,000,000
Exercise price required percentage of fair market value	100.00%
Award vesting period	4 years
Intrinsic value of options exercised	$ 300,000	$ 300,000	$ 600,000
Cash received from exercise of stock options	400,000	200,000	600,000
Fair value of options vested	10,600,000	8,600,000	6,500,000
Capitalized costs	0	0	0
Tax benefit from compensation expense	0	$ 0	$ 0
Compensation cost not yet recognized	$ 4,400,000
Compensation cost not yet recognized, period for recognition	1 year 2 months
Stock Option Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual terms	5 years
Stock Option Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual terms	7 years
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, Shares Authorized for Purchase	$ 25,000
Employee Stock Purchase Plan, Purchase Discount, Percent	85.00%
Employee Stock Purchase Plan, Shares Reserved for Future Issuance				300,000
Issuance of common stock from ESPP purchase (in shares)	121,104
2013 Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual terms	7 years
2013 Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual terms	10 years

SHARE-BASED COMPENSATION (Det48

SHARE-BASED COMPENSATION (Details 2) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of year (in shares) | shares	2,813,342
Granted (in shares) | shares	970,226
Exercise of options (in shares) | shares	(45,573)
Canceled (in shares) | shares	(415,908)
Expired (in shares) | shares	(17,906)
Balance, end of year (in shares) | shares	3,304,181
Options exercisable, end of year (in shares) | shares	1,843,808
Vested and unvested expected to vest options outstanding (in shares) | shares	3,304,181
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Balance, beginning of year (in dollars per share) | $ / shares	$ 16.57
Granted (in dollars per share) | $ / shares	5.36
Exercised (in dollars per share) | $ / shares	8.74
Canceled (in dollars per share) | $ / shares	14.47
Expired (in dollars per share) | $ / shares	12.50
Balance, end of year (in dollars per share) | $ / shares	13.67
Options exercisable, end of year (in dollars per share) | $ / shares	16.28
Vested and unvested expected to vest options outstanding, Weighted-Average Exercise Price (in dollars per share) | $ / shares	$ 13.67
Options outstanding, Weighted-Average Remaining Contractual Term (years)	7 years 2 months
Options exercisable, Weighted-Average Remaining Contractual Term (years)	6 years 1 month
Options vested and expected to vest, Weighted-Average Remaining Contractual Term (years)	7 years 2 months
Options outstanding, Aggregate Intrinsic Value | $	$ 21
Options exercisable, Aggregate Intrinsic Value | $	7.3
Options vested and expected to vest, Aggregate Intrinsic Value | $	$ 21

SHARE-BASED COMPENSATION (Det49

SHARE-BASED COMPENSATION (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 6,786	$ 10,624	$ 10,254
Research and development expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,192	5,461	3,669
General and administrative expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,594	$ 5,163	$ 6,585

SHARE-BASED COMPENSATION (Det50

SHARE-BASED COMPENSATION (Details 4) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.10%	1.50%	1.50%
Dividend yield	0.00%	0.00%	0.00%
Volatility factor	96.00%	101.70%	104.30%
Expected term (in years)	6 years	6 years	6 years
Weighted average estimated fair value per share	$ 4.17	$ 13.32	$ 19.44

EMPLOYEE BENEFIT PLAN (Details)

EMPLOYEE BENEFIT PLAN (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Percentage of employee contributions matched	4.00%
Maximum employer contribution per employee	$ 2,500
Matching contribution amount	$ 100,000	$ 100,000	$ 100,000

INCOME TAXES (Details)

INCOME TAXES (Details)	12 Months Ended
	Dec. 31, 2017USD ($)ongoing_tax_audit	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Net loss before tax	$ (70,430,000)	$ (83,118,000)	$ (64,544,000)
Statutory combined US federal and state tax rate (2012 - statutory combined Canadian federal and provincial tax rate)	34.00%	34.00%	34.00%
Statutory federal and provincial taxes	$ (23,946,000)	$ (28,260,000)	$ (21,945,000)
Effect of change in valuation allowance	(4,154,000)	28,446,000	22,350,000
Non-deductible share-based compensation	695,000	1,247,000	923,000
Tax credits	(2,563,000)	(2,906,000)	(2,430,000)
Share issue costs - temporary difference	0	(78,000)	(184,000)
Write off of Methylgene US NOL	307,000	0	0
Differential in income tax rates of foreign subsidiary	(169,000)	261,000	31,000
Change in tax rate	303,000	0	0
Tax Cuts and Jobs Act		0	0
Uncertain tax positions	646,000	3,921,000	1,961,000
Return to provision and other true-ups	368,000	(2,619,000)	(899,000)
Other differences	(56,000)	(12,000)	193,000
Income tax expense (benefit)	0	0	0
Deferred tax asset
Tangible and intangible depreciable assets	17,927,000	990,000
Stock compensation	4,976,000	6,635,000
Provisions	611,000	853,000
Net operating loss carry forwards	44,598,000	66,489,000
Capital loss carryforward	83,000	51,000
Scientific research and experimental development expenditures	5,467,000	5,531,000
Research and development tax credits	7,016,000	4,266,000
Total gross deferred tax assets	80,678,000	84,815,000
Less valuation allowance	(80,678,000)	(84,815,000)
Net deferred tax assets	0	0
Additional disclosures
Amount of increase in valuation allowance	4,100,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Accrual for interest or penalties on tax matters	$ 0
Number of ongoing tax audits | ongoing_tax_audit	0
Tax Cuts And Jobs Act Of 2017, change in tax rate, deferred tax asset, expense	$ 28,569,000
Domestic Tax Authority
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense (benefit)	0	0	0
Canadian Federal
Additional disclosures
Scientific research and experimental development expenses deductible for income tax purposes	19,900,000	19,900,000
Net operating loss carry forwards (NOLs)	80,567,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	1,095,000	509,000	42,000
Gross increase — current period tax positions	588,000	598,000	445,000
Gross decrease — prior period tax positions	0	(9,000)	(4,000)
Gross increase — prior period tax positions	11,000	0	26,000
Expiration of statute of limitations	(1,000)	(3,000)	0
Unrecognized tax positions, end of year	1,693,000	1,095,000	509,000
Canadian Federal | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	5,907,000
Canadian Federal | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	7,059,000
Canadian Federal | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	13,308,000
Canadian Federal | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	18,623,000
Canadian Federal | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	32,401,000
Canadian Federal | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	1,084,000
Canadian Federal | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	777,000
Canadian Federal | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	1,408,000
Canadian Provincial
Additional disclosures
Scientific research and experimental development expenses deductible for income tax purposes	21,600,000	21,600,000
Net operating loss carry forwards (NOLs)	79,947,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	7,333,000	2,274,000	18,000
Gross increase — current period tax positions	227,000	195,000	259,000
Gross decrease — prior period tax positions	(3,000)	0	(3,000)
Gross increase — prior period tax positions	0	4,866,000	2,000,000
Expiration of statute of limitations	(1,000)	(2,000)	0
Unrecognized tax positions, end of year	7,556,000	$ 7,333,000	$ 2,274,000
Canadian Provincial | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	5,985,000
Canadian Provincial | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	7,066,000
Canadian Provincial | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	12,433,000
Canadian Provincial | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	19,385,000
Canadian Provincial | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	31,809,000
Canadian Provincial | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	1,084,000
Canadian Provincial | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	777,000
Canadian Provincial | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	1,408,000
US Federal
Additional disclosures
Net operating loss carry forwards (NOLs)	110,283,000
US Federal | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	2,225,000
US Federal | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	7,276,000
US Federal | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	53,359,000
US Federal | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	23,379,000
US Federal | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	24,044,000
US Federal | Research Tax Credit Carryforward
Additional disclosures
Tax credit carryforward	7,200,000
US State
Additional disclosures
Net operating loss carry forwards (NOLs)	77,344,000
US State | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	2,232,000
US State | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	22,162,000
US State | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	52,950,000
US State | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | Research Tax Credit Carryforward
Additional disclosures
Tax credit carryforward	$ 2,900,000

INVESTMENT TAX CREDITS (Details

INVESTMENT TAX CREDITS (Details) - Canadian Federal $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
INVESTMENT TAX CREDITS
Non-refundable ITCs related to scientific research and development expenditures	$ 3,907
2,030
INVESTMENT TAX CREDITS
Non-refundable ITCs related to scientific research and development expenditures	764
2,031
INVESTMENT TAX CREDITS
Non-refundable ITCs related to scientific research and development expenditures	1,000
2,032
INVESTMENT TAX CREDITS
Non-refundable ITCs related to scientific research and development expenditures	1,125
2,033
INVESTMENT TAX CREDITS
Non-refundable ITCs related to scientific research and development expenditures	$ 1,018

COMMITMENTS AND CONTINGENCIES54

COMMITMENTS AND CONTINGENCIES (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015	Jun. 24, 2014ft²
Future minimum annual payments
2,018	$ 289,000
2,019	26,000
Thereafter	0
Total minimum lease payments	315,000
Operating Leases, Rent Expense, Net [Abstract]
Lease expense	700,000	$ 800,000	$ 600,000
Building
Operating Leased Assets [Line Items]
Area of space leased | ft²					18
Monthly lease rent	$ 24,100
Annual rent increase (percent)				3.00%

QUARTERLY FINANCIAL DATA (Detai

QUARTERLY FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Operating loss	$ (18,228)	$ (16,601)	$ (18,616)	$ (18,090)	$ (19,853)	$ (19,581)	$ (22,227)	$ (22,118)	$ (71,535)	$ (83,779)	$ (64,714)
Net loss	$ (17,895)	$ (16,350)	$ (18,339)	$ (17,846)	$ (19,722)	$ (19,421)	$ (22,061)	$ (21,914)	$ (70,430)	$ (83,118)	$ (64,544)
Loss per share, basic (in US$ per share)	$ (0.67)	$ (0.65)	$ (0.74)	$ (0.73)	$ (0.99)	$ (0.97)	$ (1.11)	$ (1.13)	$ (2.78)	$ (4.20)	$ (3.82)