Geron (GERN) 10-K 16 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 07, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	GERON CORP
Entity Central Index Key	886,744
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 438,713,000
Entity Common Stock, Shares Outstanding		160,654,027
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	GERN

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 16,335	$ 12,810
Restricted cash	268	268
Marketable securities	78,351	102,035
Interest and other receivables	436	475
Prepaid assets	580	524
Total current assets	95,970	116,112
Noncurrent marketable securities	14,241	13,954
Property and equipment, net	102	183
Total assets	110,313	130,249
Current liabilities:
Accounts payable	503	225
Accrued compensation and benefits	3,385	2,843
Accrued collaboration charges	1,702	3,367
Accrued liabilities	926	1,434
Total current liabilities	6,516	7,869
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 3,000,000 shares authorized; no shares issued and outstanding at December 31, 2017 and 2016
Common stock, $0.001 par value; 300,000,000 shares authorized; 159,877,239 and 159,158,636 shares issued and outstanding at December 31, 2017 and 2016, respectively	160	159
Additional paid-in capital	1,089,684	1,080,198
Accumulated deficit	(985,840)	(957,924)
Accumulated other comprehensive loss	(207)	(53)
Total stockholders' equity	103,797	122,380
Total liabilities and stockholders' equity	$ 110,313	$ 130,249

BALANCE SHEETS (Parenthetical)

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	3,000,000	3,000,000
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	300,000,000	300,000,000
Common stock, shares issued	159,877,239	159,158,636
Common stock, shares outstanding	159,877,239	159,158,636

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Collaboration revenue			$ 35,000
License fees and royalties	$ 1,065	$ 6,162	1,371
Total revenues	1,065	6,162	36,371
Operating expenses:
Research and development	11,033	18,047	17,831
Restructuring charges			1,306
General and administrative	19,287	18,761	17,793
Total operating expenses	30,320	36,808	36,930
Loss from operations	(29,255)	(30,646)	(559)
Unrealized gain on derivatives			16
Interest and other income	1,416	1,192	677
Interest and other expense	(77)	(83)	(88)
Net (loss) income	$ (27,916)	$ (29,537)	$ 46
Net (loss) income per share:
Basic	$ (0.18)	$ (0.19)	$ 0
Diluted	$ (0.18)	$ (0.19)	$ 0
Shares used in computing net (loss) income per share:
Basic	159,224,986	159,045,644	158,036,162
Diluted	159,224,986	159,045,644	162,663,894

STATEMENTS OF COMPREHENSIVE LOS

STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (27,916)	$ (29,537)	$ 46
Net unrealized (loss) gain on marketable securities	(154)	160	(129)
Comprehensive loss	$ (28,070)	$ (29,377)	$ (83)

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balances at Dec. 31, 2014	$ 130,712	$ 157	$ 1,059,072	$ (928,433)	$ (84)
Balances (in shares) at Dec. 31, 2014		157,429,871
Increase (Decrease) in Stockholders' Equity
Net (loss) income	46			46
Other comprehensive (loss) income	(129)				(129)
Stock-based compensation related to issuance of common stock and options in exchange for services	364		364
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		18,077
Issuance of common stock upon exercise of warrants	881	$ 1	880
Issuance of common stock upon exercise of warrants (in shares)		235,000
Issuances of common stock under equity plans	1,694	$ 1	1,693
Issuances of common stock under equity plans (in shares)		1,098,411
Stock-based compensation for equity- based awards to employees and directors	8,397		8,397
401(k) contribution	161		161
Balances at Dec. 31, 2015	142,126	$ 159	1,070,567	(928,387)	(213)
Balances (in shares) at Dec. 31, 2015		158,781,359
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(29,537)			(29,537)
Other comprehensive (loss) income	160				160
Stock-based compensation related to issuance of common stock and options in exchange for services	156		156
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		21,541
Issuances of common stock under equity plans	1,169		1,169
Issuances of common stock under equity plans (in shares)		355,736
Stock-based compensation for equity- based awards to employees and directors	8,245		8,245
401(k) contribution	61		61
Balances at Dec. 31, 2016	$ 122,380	$ 159	1,080,198	(957,924)	(53)
Balances (in shares) at Dec. 31, 2016	159,158,636	159,158,636
Increase (Decrease) in Stockholders' Equity
Net (loss) income	$ (27,916)			(27,916)
Other comprehensive (loss) income	(154)				(154)
Issuance of common stock in connection with at market offering, net of issuance costs of $114	1,060	$ 1	1,059
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		614,230
Stock-based compensation related to issuance of common stock and options in exchange for services	200		200
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		72,066
Issuances of common stock under equity plans	51		51
Issuances of common stock under equity plans (in shares)		32,307
Stock-based compensation for equity- based awards to employees and directors	8,144		8,144
401(k) contribution	32		32
Balances at Dec. 31, 2017	$ 103,797	$ 160	$ 1,089,684	$ (985,840)	$ (207)
Balances (in shares) at Dec. 31, 2017	159,877,239	159,877,239

STATEMENTS OF STOCKHOLDERS' EQ7

STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Statement Of Stockholders Equity [Abstract]
Issuance costs	$ 114

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net (loss) income	$ (27,916)	$ (29,537)	$ 46
Adjustments to reconcile net (loss) income to net cash used in operating activities:
Depreciation and amortization	76	81	56
Loss (gain) on retirement/sales of property and equipment	5	(16)
Accretion and amortization on investments, net	273	552	2,098
Loss on sales of marketable securities			1
Stock-based compensation for services by non-employees	200	156	364
Stock-based compensation for employees and directors	8,144	8,245	8,397
Amortization related to 401(k) contributions	32	61	161
Unrealized gain on derivatives			(16)
Changes in assets and liabilities:
Interest and other receivables	39	731	(243)
Prepaid assets	(56)	123	89
Accounts payable	278	65	(873)
Accrued compensation and benefits	542	(183)	(1,187)
Accrued collaboration charges	(1,665)	1,039	2,328
Accrued liabilities	(508)	314	(417)
Deferred revenue			(35,000)
Net cash used in operating activities	(20,556)	(18,369)	(24,196)
Cash flows from investing activities:
Restricted cash transfer		(1)	(1)
Purchases of property and equipment		(57)	(90)
Proceeds from sales of property and equipment		16
Purchases of marketable securities	(100,006)	(129,250)	(206,459)
Proceeds from sales/calls of marketable securities			4,242
Proceeds from maturities of marketable securities	122,976	138,054	202,381
Net cash provided by investing activities	22,970	8,762	73
Cash flows from financing activities:
Proceeds from issuances of common stock	1,111	1,169	2,575
Net cash provided by financing activities	1,111	1,169	2,575
Net increase (decrease) in cash and cash equivalents	3,525	(8,438)	(21,548)
Cash and cash equivalents at the beginning of the period	12,810	21,248	42,796
Cash and cash equivalents at the end of the period	$ 16,335	$ 12,810	$ 21,248

ORGANIZATION AND SUMMARY OF SIG

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization Geron Corporation, or we or Geron, was incorporated in the State of Delaware on November 28, 1990. We are a biopharmaceutical company that currently supports the clinical stage development of a telomerase inhibitor, imetelstat, in hematologic myeloid malignancies, by Janssen Biotech, Inc., or Janssen. Principal activities to date have included obtaining financing, securing operating facilities and conducting research and development. In November 2014, we entered into an exclusive collaboration and license agreement, or the Collaboration Agreement, with Janssen to develop and commercialize imetelstat worldwide for all indications in oncology, including hematologic myeloid malignancies, and all other human therapeutic uses. Under the Collaboration Agreement, Janssen is wholly responsible for the worldwide development, manufacturing, seeking regulatory approval for and commercialization of, imetelstat, which was our sole product candidate. Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) by the weighted‑average number of shares of common stock outstanding during the periods presented, without consideration for potential common shares. Diluted net income per share is calculated by adjusting the weighted‑average number of shares of common stock outstanding for the dilutive effect of potential common shares outstanding for the periods presented, as determined using the treasury‑stock method. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase our common stock. For periods in which we have incurred a net loss, potential common shares outstanding for the periods presented, as determined using the treasury‑stock method, are excluded, as their effect would be anti‑dilutive, resulting in the same number of shares being used for the calculation of basic and diluted net loss per share. For all periods presented in the accompanying statements of operations, the net income (loss) applicable to common stockholders is equal to the reported net income (loss). Year Ended December 31, (In thousands, except share and per share data) 2017 2016 2015 Net (loss) income $ (27,916 ) $ (29,537 ) $ 46 Weighted-average shares: Basic 159,224,986 159,045,644 158,036,162 Effect of dilutive securities: Stock options and restricted stock awards — — 4,627,732 Diluted 159,224,986 159,045,644 162,663,894 Net (loss) income per share: Basic $ (0.18 ) $ (0.19 ) $ 0.00 Diluted $ (0.18 ) $ (0.19 ) $ 0.00 Because we were in a net loss position for 2017 and 2016, 2,389,310 and 3,023,520 potential common shares, respectively, related to outstanding stock options and restricted stock awards (as determined using the treasury‑stock method at the estimated average market value) were excluded from the diluted net loss per share calculation as their effect would have been anti‑dilutive. In addition for 2017, 2016 and 2015, 14,475,616, 11,352,766 and 9,375,851 potentially dilutive securities, respectively, were excluded from the treasury‑stock method and calculation of diluted net income (loss) per share as their effect would have been anti‑dilutive. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) Use of Estimates The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, we evaluate our estimates, including those related to accrued liabilities, revenue recognition, fair value of marketable securities, income taxes, and stock-based compensation. We base our estimates on historical experience and on various other market specific and relevant assumptions that we believe to be reasonable under the circumstances. Actual results could differ from those estimates. Fair Value of Financial Instruments Cash Equivalents and Marketable Securities We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. We are subject to credit risk related to our cash equivalents and marketable securities. We place our cash and cash equivalents in money market funds, commercial paper, corporate notes and cash operating accounts. Our marketable securities include U.S. government‑sponsored enterprise securities, commercial paper and corporate notes. We classify our marketable securities as available‑for‑sale. We record available‑for‑sale securities at fair value with unrealized gains and losses reported in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included in interest and other income and are derived using the specific identification method for determining the cost of securities sold and have been insignificant to date. Dividend and interest income are recognized when earned and included in interest and other income in our statements of operations. We recognize a charge when the declines in the fair values below the amortized cost basis of our available‑for‑sale securities are judged to be other‑than‑temporary. We consider various factors in determining whether to recognize an other‑than‑temporary charge, including whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. Declines in market value judged as other‑than‑temporary result in a charge to interest and other income. We have not recorded any other‑than‑temporary impairment charges on our available‑for‑sale securities for the years ended December 31, 2017, 2016 and 2015. See Note 2 on Fair Value Measurements. Cost Method Investments We use the cost method of accounting for non-marketable equity securities where our ownership represents less than 20% of such entity, and we cannot exert significant influence over its operations. These securities are carried at cost and adjusted for impairments. Fair Value of Derivatives Non‑employee options classified as derivative liabilities are marked to fair value at each financial reporting date with any resulting changes in fair value being recorded in the statements of operations as unrealized gain (loss) on derivatives. The non‑employee options continue to be reported as a derivative liability until such time as the instruments are exercised or expire, at which time these instruments are marked to fair value and reclassified from liabilities to stockholders’ equity. As of March 31, 2015, all non‑employee options classified as derivative liabilities expired unexercised. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue Recognition We recognize revenue for each unit of accounting when all of the following criteria have been met: (a) persuasive evidence of an arrangement exists, (b) delivery has occurred or services have been rendered, (c) the seller’s price to the buyer is fixed or determinable, and (d) collectability is reasonably assured. Amounts received prior to satisfying these revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as noncurrent deferred revenue. License and/or Collaboration Agreements In addition to the Collaboration Agreement (which is more fully described in Note 4 on License Agreements), we have entered into several license or collaboration agreements with various oncology, diagnostics, research tools and biologics production companies. Economic terms in these agreements may include non‑refundable upfront license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, cost‑sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. In applying the appropriate revenue recognition guidance related to these agreements, we first assess whether the arrangement contains multiple elements. In this evaluation, we consider: (i) the deliverables included in the arrangement and (ii) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires us to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in our control. In assessing whether an item has standalone value, we consider factors such as the research, manufacturing and commercialization capabilities of the collaboration partner or licensee and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner or licensee can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. We then apply the applicable revenue recognition criteria noted above to each of the separate units of accounting in determining the appropriate period and pattern of recognition. We determine how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under relevant accounting guidance. The estimated fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor‑specific‑objective evidence and third‑party evidence are not available. Upfront non‑refundable signing, license or non‑exclusive option fees are recognized as revenue: (i) when rights to use the intellectual property have been delivered, if the license has standalone value from the other deliverables to be provided under the agreement, or (ii) over the term of the agreement if we have continuing performance obligations, as the arrangement would be accounted for as a single unit of accounting. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either (1) our performance to achieve the milestone or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms (including other potential milestone consideration) within the arrangement. We consider various factors, such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone, in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestone payments for milestones that are considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestone payments for milestones that are not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met. Our license and collaboration agreements with certain partners also provide for contingent payments to us based solely upon the performance of the respective partner. For such contingent amounts, we recognize the payments as revenue when earned under the applicable contract, which is generally upon completion of performance by the respective partner, provided that collection is reasonably assured. Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collection is reasonably assured. If royalties cannot be reasonably estimated or collection of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments is accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met and we have no performance obligations related to the milestone. Cost‑sharing expenses are recorded as earned or owed based on the performance requirements by both parties under the respective contracts. For arrangements in which we and our collaboration partner in the agreement are exposed to significant risks and rewards that depend on the commercial success of the activity, we recognize payments between the parties on a net basis and record such amounts as a reduction or addition to research and development expense. For arrangements in which we have agreed to perform certain research and development services for our collaboration partner and are not exposed to significant risks and rewards that depend on the commercial success of the activity, we recognize the respective cost reimbursements as revenue under the collaborative agreement as the related research and development services are rendered. Restricted Cash Restricted cash consists of funds maintained in a separate certificate of deposit account for credit card purchases. Research and Development Expenses Research and development expenses consist of expenses incurred in identifying, developing and testing product candidates resulting from our independent efforts as well as efforts associated with collaborations. These expenses include, but are not limited to, in‑process research and development acquired in an asset acquisition and deemed to have no alternative future use, payroll and personnel expense, lab supplies, preclinical studies, clinical trials, including support for investigator‑sponsored clinical trials, raw materials to manufacture clinical trial drugs, manufacturing costs for research and clinical trial materials, sponsored research at other labs, consulting, costs to maintain technology licenses, our proportionate share of research and development costs under cost‑sharing arrangements with collaboration partners and research‑related overhead. Research and development costs are expensed as incurred, including costs incurred under our collaboration and/or license agreements. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) For the clinical development activities being conducted by Janssen under the Collaboration Agreement, we monitor patient enrollment levels and related activities to the extent possible through discussions with Janssen personnel and base our estimates on the best information available at the time. However, additional information may become available to us which would allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. Depreciation and Amortization We record property and equipment at cost and calculate depreciation using the straight‑line method over the estimated useful lives of the assets, generally four years. Leasehold improvements are amortized over the shorter of the estimated useful life or remaining term of the lease. Stock‑Based Compensation We maintain various stock incentive plans under which stock options and restricted stock awards are granted to employees, directors and consultants. We also have an employee stock purchase plan for all eligible employees. We recognize stock‑based compensation expense based on the grant-date fair values of these instruments on a straight‑line basis over the requisite service period, which is generally the vesting period. The determination of grant-date fair values for our stock options and employee stock purchases using the Black Scholes option‑pricing model is affected by our stock price as well as assumptions regarding a number of complex and subjective variables. The grant-date fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. For our non‑employee stock‑based awards, the measurement date on which the fair value of the stock‑based award is calculated is equal to the earlier of: (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. We recognize stock‑based compensation expense for the fair value of the vested portion of non‑employee stock‑based awards in our statements of operations. For additional information, see Note 8 on Stockholders’ Equity. Accumulated Other Comprehensive Loss Accumulated other comprehensive loss includes certain changes in stockholders’ equity which are excluded from net income (loss). Accumulated other comprehensive loss on our balance sheets as of December 31, 2017 and 2016 is solely comprised of net unrealized losses on marketable securities. Income Taxes We maintain deferred tax assets and liabilities that reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and are subject to tests of recoverability. Our deferred tax assets include net operating loss carryforwards, research credits and capitalized research and development. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. Our net deferred tax asset has been fully offset by a valuation allowance because of our history of losses. Any potential accrued interest and penalties related to unrecognized tax benefits would be recorded as income tax expense. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) Concentrations of Customers and Suppliers The majority of our revenues was earned in the United States. Two customers accounted for approximately 39% of our 2017 revenues. Approximately 81% of our 2016 revenues represented an upfront payment from Janssen Pharmaceuticals, Inc., or Janssen Pharmaceuticals, in connection with a license agreement signed in September 2016, or the License Agreement. Approximately 96% of our 2015 revenues represented an upfront payment from Janssen under the imetelstat Collaboration Agreement. In accordance with the Collaboration Agreement, Janssen is now responsible for the manufacture and management of the supply of imetelstat on a global basis for clinical trials and, after any regulatory approval, all commercial activities. Janssen contracts third‑party manufacturers to produce GMP‑grade drugs for preclinical and clinical studies. Janssen also contracts for starting materials to supply those manufacturers and for its own use. Certain development and clinical activities may be delayed if Janssen is unable to obtain sufficient quantities of starting materials or GMP‑grade drugs from current third‑party suppliers or other third‑party sources. Segment Information Our executive management team represents our chief decision maker. We view our operations as a single segment, the development of therapeutic products for oncology. As a result, the financial information disclosed herein materially represents all of the financial information related to our principal operating segment. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update No. 2014-09, or ASU 2014-09, which created Accounting Standards Codification Topic 606, Revenue from Contracts with Customers Revenue Recognition Revenue From Contracts With Customers: Principal vs. Agent Considerations Revenue From Contracts with Customers: Identifying Performance Obligations and Licensing Revenue From Contracts with Customers: Narrow-Scope Improvements and Practical Expedients Revenue from Contracts with Customers Technical Corrections and Improvements to Topic 606, The new revenue standard is principles-based and the interpretation of those principles may vary from company to company based on their unique circumstances. It is possible that interpretations, industry practice, and guidance may evolve as companies and the accounting profession work to implement this new standard. We have assessed the differences in accounting for our existing contracts under the new guidance compared to current revenue accounting standards. We have not identified any material differences in the accounting treatment under ASU 2014-09 compared to the current accounting treatment for the Collaboration Agreement with Janssen and the License Agreement with Janssen Pharmaceuticals, which are our most significant license agreements. With the adoption of ASU 2014-09, we expect royalty revenues from product sales by licensees of our human telomerase reverse transcriptase, or hTERT, technology and cell-based research products to be recognized earlier than under our current accounting policy for revenue recognition. Accordingly, we expect to record a one-time cumulative catch-up adjustment in 2018 to reflect 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) estimated royalty revenues on product sales earned in 2017 for which payments have not yet been received. We do not expect that the adoption of ASU 2014-09 will have a material impact on our financial statements and related disclosures. In January 2016, the FASB issued Accounting Standards Update No. 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) In August 2016, the FASB issued Accounting Standards Update No. 2016-15, Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued Accounting Standards Update No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash In May 2017, the FASB issued Accounting Standards Update No. 2017-09, Compensation — Stock Compensation: Scope of Modification Accounting

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	2. FAIR VALUE MEASUREMENTS Cash Equivalents and Marketable Securities Cash equivalents, restricted cash and marketable securities by security type at December 31, 2017 were as follows: Gross Gross Amortized Unrealized Unrealized Estimated (In thousands) Cost Gains Losses Fair Value Included in cash and cash equivalents: Money market funds $ 11,030 $ — $ — $ 11,030 Commercial paper 2,242 — — 2,242 Corporate notes 1,750 — (1 ) 1,749 $ 15,022 $ — $ (1 ) $ 15,021 Restricted cash: Certificate of deposit $ 268 $ — $ — $ 268 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 12,500 $ — $ (40 ) $ 12,460 Commercial paper (due in less than one year) 10,928 4 (1 ) 10,931 Corporate notes (due in less than one year) 55,067 — (107 ) 54,960 Corporate notes (due in one to two years) 14,303 — (62 ) 14,241 $ 92,798 $ 4 $ (210 ) $ 92,592 Cash equivalents, restricted cash and marketable securities by security type at December 31, 2016 were as follows: Gross Gross Amortized Unrealized Unrealized Estimated (In thousands) Cost Gains Losses Fair Value Included in cash and cash equivalents: Money market funds $ 11,193 $ — $ — $ 11,193 Restricted cash: Certificate of deposit $ 268 $ — $ — $ 268 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 5,000 $ — $ (3 ) $ 4,997 Government-sponsored enterprise securities (due in one to two years) 12,500 — (42 ) 12,458 Commercial paper (due in less than one year) 31,024 50 (5 ) 31,069 Corporate notes (due in less than one year) 66,012 4 (47 ) 65,969 Corporate notes (due in one to two years) 1,506 — (10 ) 1,496 $ 116,042 $ 54 $ (107 ) $ 115,989 2. FAIR VALUE MEASUREMENTS (Continued) Cash equivalents and marketable securities with unrealized losses at December 31, 2017 and 2016 were as follows: Less Than 12 Months 12 Months or Greater Total Gross Gross Gross Estimated Unrealized Estimated Unrealized Estimated Unrealized (In thousands) Fair Value Losses Fair Value Losses Fair Value Losses As of December 31, 2017: Government-sponsored enterprise securities (due in less than one year) $ — $ — $ 12,460 $ (40 ) $ 12,460 $ (40 ) Commercial paper (due in less than one year) 7,717 (1 ) — — 7,717 (1 ) Corporate notes (due in less than one year) 55,210 (106 ) 1,499 (2 ) 56,709 (108 ) Corporate notes (due in one to two years) 14,241 (62 ) — — 14,241 (62 ) $ 77,168 $ (169 ) $ 13,959 $ (42 ) $ 91,127 $ (211 ) As of December 31, 2016: Government-sponsored enterprise securities (due in less than one year) $ 4,997 $ (3 ) $ — $ — $ 4,997 $ (3 ) Government-sponsored enterprise securities (due in one to two years) 12,458 (42 ) — — 12,458 (42 ) Commercial paper (due in less than one year) 8,365 (5 ) — — 8,365 (5 ) Corporate notes (due in less than one year) 39,218 (37 ) 6,944 (10 ) 46,162 (47 ) Corporate notes (due in one to two years) 1,496 (10 ) — — 1,496 (10 ) $ 66,534 $ (97 ) $ 6,944 $ (10 ) $ 73,478 $ (107 ) The gross unrealized losses related to government‑sponsored enterprise securities, commercial paper and corporate notes as of December 31, 2017 and 2016 were due to changes in interest rates. We determined that the gross unrealized losses on our cash equivalents and marketable securities as of December 31, 2017 and 2016 were temporary in nature. We review our investments quarterly to identify and evaluate whether any investments have indications of possible impairment. Factors considered in determining whether a loss is temporary include the length of time and extent to which the fair value has been less than the cost basis and whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. We currently do not intend to sell these securities before recovery of their amortized cost bases. Fair Value on a Recurring Basis We categorize financial instruments recorded at fair value on our balance sheets based upon the level of judgment associated with inputs used to measure their fair value. The categories are as follows: Level 1 — Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. An active market for the asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 — Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3 — Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. 2. FAIR VALUE MEASUREMENTS (Continued) A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Below is a description of the valuation methodologies used for financial instruments measured at fair value on our balance sheets, including the category for such financial instruments. Money market funds are categorized as Level 1 within the fair value hierarchy as their fair values are based on quoted prices available in active markets. U.S. government‑sponsored enterprise securities, commercial paper and corporate notes are categorized as Level 2 within the fair value hierarchy as their fair values are estimated by using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2017 and 2016 and indicates the fair value category assigned. Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs (In thousands) Level 1 Level 2 Level 3 Total As of December 31, 2017: Money market funds ( 1) $ 11,030 $ — $ — $ 11,030 Government-sponsored enterprise securities ( 2) — 12,460 — 12,460 Commercial paper ( 1)(2) — 13,173 — 13,173 Corporate notes ( 1)(2)(3) — 70,950 — 70,950 Total $ 11,030 $ 96,583 $ — $ 107,613 As of December 31, 2016: Money market funds ( 1) $ 11,193 $ — $ — $ 11,193 Government-sponsored enterprise securities ( 2)(3) — 17,455 — 17,455 Commercial paper ( 2) — 31,069 — 31,069 Corporate notes ( 2)(3) — 67,465 — 67,465 Total $ 11,193 $ 115,989 $ — $ 127,182 (1) Included in cash and cash equivalents on our balance sheets. (2) Included in current portion of marketable securities on our balance sheets. (3) Included in noncurrent portion of marketable securities on our balance sheets. Cost Method Investment In December 2007, we granted a license to our hTERT technology for use in human diagnostics to Sienna Cancer Diagnostics Limited, or Sienna, which was a privately held company in Australia. In connection with the license, we received 13,842,625 ordinary shares in Sienna which we recorded at a zero cost basis under the cost method of accounting. On August 3, 2017, Sienna became a publicly traded company on the Australian Securities Exchange Limited, or ASX, under the ticker symbol SDX. Since our shares are subject to a 24-month trading restriction from the effective date of Sienna’s listing on the ASX, we account for our investment in Sienna under the cost method of accounting since there is no readily determinable fair value for our shares, and such shares do not meet the definition of a marketable security. With the adoption of ASU 2016-01 and ASU 2018-03 in 2018, the method in which we account for our shares of Sienna will change. For additional information on ASU 2016-01 and ASU 2018-03, see the section entitled “Recent Accounting Pronouncements Not Yet Effective” in Note 1 on Organization and Summary of Significant Accounting Policies. 2. FAIR VALUE MEASUREMENTS (Continued) Credit Risk We currently place our cash, restricted cash, cash equivalents and marketable securities with four financial institutions in the United States. Generally, these deposits may be redeemed upon demand and therefore, bear minimal risk. Deposits with banks may exceed the amount of insurance provided on such deposits. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash equivalents and marketable securities. Cash equivalents and marketable securities currently consist of money market funds, U.S. government‑sponsored enterprise securities, commercial paper and corporate notes. Our investment policy, approved by the audit committee of our board of directors, limits the amount we may invest in any one type of investment issuer, thereby reducing credit risk concentrations.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
PROPERTY AND EQUIPMENT	3. PROPERTY AND EQUIPMENT Property and equipment, stated at cost, is comprised of the following: December 31, (In thousands) 2017 2016 Furniture and computer equipment $ 711 $ 1,268 Lab equipment — 12 Leasehold improvements 111 111 822 1,391 Less accumulated depreciation and amortization (720 ) (1,208 ) $ 102 $ 183

LICENSE AGREEMENTS

LICENSE AGREEMENTS	12 Months Ended
	Dec. 31, 2017
License Agreement Disclosure [Abstract]
LICENSE AGREEMENTS	4. LICENSE AGREEMENTS Janssen Biotech, Inc. Collaboration and License Agreement On November 13, 2014, we and Janssen entered into the Collaboration Agreement under which we granted to Janssen exclusive worldwide rights to develop and commercialize imetelstat for all human therapeutic uses, including hematologic myeloid malignancies. Upon the effectiveness of the Collaboration Agreement, we received $35,000,000 from Janssen as an upfront payment, which we classified as deferred revenue upon receipt. Under the Collaboration Agreement, Janssen is wholly responsible for the development, manufacturing, seeking regulatory approval for and commercialization of, imetelstat worldwide. Janssen is currently conducting two clinical trials of imetelstat: a Phase 2 trial in myelofibrosis, referred to as IMbark, and a Phase 2/3 trial in myelodysplastic syndromes, referred to as IMerge. Development costs for IMbark and IMerge are being shared between us and Janssen on a 50/50 basis. Additionally, under the terms of the Collaboration Agreement, we remain responsible for prosecuting, at Janssen’s direction, the patents licensed to Janssen at the time we entered into the Collaboration Agreement, with costs shared between us and Janssen on a 50/50 basis. The cost‑sharing arrangement with Janssen began in January 2015. As of December 31, 2017, accrued collaboration charges of $1,702,000 on our balance sheet represent the net amount owed to Janssen for our proportionate share of development costs incurred by Janssen under the Collaboration Agreement for the three months ended December 31, 2017. Following completion of the protocol-specified primary analysis of IMbark by Janssen, if completed, we expect Janssen to notify us of their decision, or a Continuation Decision, as to whether they elect to maintain the license rights granted to them under the Collaboration Agreement and continue to advance the development of imetelstat in any indication. In the event that IMbark is terminated early, or placed on clinical hold or suspended by a regulatory authority for an extended period of time, then Janssen must instead notify us of their Continuation Decision by the date that is approximately 24 months after the initiation of IMerge. 4. LICENSE AGREEMENTS (Continued) In the event that Janssen provides an affirmative Continuation Decision, we then would have an option, or the U.S. Opt‑In Rights, to share further U.S. development and promotion costs, including our share of development costs incurred to date by Janssen beyond IMbark or IMerge, in exchange for higher tiered royalty rates and higher future development and regulatory milestone payments if imetelstat is successfully developed and approved. If we exercise the U.S. Opt‑In Rights, then we and Janssen would share U.S. development and promotion costs beyond IMbark and IMerge on a 20/80 basis (Geron 20%, Janssen 80%), we would receive a $65,000,000 milestone payment, or the Continuation Fee, at the time of an affirmative Continuation Decision, and would be eligible to receive additional potential payments of up to $470,000,000 for the achievement of certain development and regulatory milestones, up to $350,000,000 for the achievement of certain sales milestones, and tiered royalties ranging from a mid‑teens up to low twenties percentage rate on worldwide net sales of imetelstat in any countries where regulatory exclusivity exists or there are valid claims under the patent rights exclusively licensed to Janssen. In addition, if we exercise the U.S. Opt‑In Rights, we then would also have a separate option, or the U.S. Co‑Promotion Option, to provide 20% of the U.S. selling effort with our sales force personnel, in lieu of funding 20% of U.S. promotion costs, upon regulatory approval and commercial launch of imetelstat in the United States. Such co‑promotion would be conducted under a Janssen prepared promotion plan, and in accordance with a co‑promotion agreement to be agreed by the parties at the time of our exercise of the U.S. Co‑Promotion Option. We would be responsible for all costs associated with establishing and maintaining our sales force in any conduct of such co‑promotion. All product sales would be booked by Janssen. If we do not exercise the U.S. Opt‑In Rights, then all further development and promotion costs beyond IMbark and IMerge would be borne by Janssen, we would receive the $65,000,000 Continuation Fee at the time of an affirmative Continuation Decision plus a $70,000,000 payment, or the Full U.S. Rights Fee, for Janssen’s retention of full U.S. rights to imetelstat, and would be eligible to receive additional potential payments of up to $415,000,000 for the achievement of certain development and regulatory milestones, up to $350,000,000 for the achievement of certain sales milestones, and tiered royalties ranging from a double‑digit up to mid‑teens percentage rate on worldwide net sales of imetelstat in any countries where regulatory exclusivity exists or there are valid claims under the patent rights exclusively licensed to Janssen. Under the terms of the Collaboration Agreement, we and Janssen have created a joint governance structure, including joint development and steering committees and working groups, to oversee and manage worldwide regulatory, development and manufacturing work under the joint clinical development plan and promotional activities (assuming we exercise the U.S. Opt‑In Rights) for imetelstat, with Janssen responsible for the operational execution of those activities. In addition, both we and Janssen may propose to the joint development committee imetelstat development for any new indications not then provided for in the joint clinical development plan and if we and Janssen agree such development should be conducted outside of the joint clinical development plan, both we and Janssen would be entitled to independently undertake such development at the developing party’s own cost, subject to the other party’s obligation to provide reimbursement for its specified portion of the development costs plus a premium following marketing approval of imetelstat in such newly proposed indication as a result of such independent development. In the event that we do not exercise the U.S. Opt‑In Rights following an affirmative Continuation Decision by Janssen, if any, the joint governance structure under the Collaboration Agreement would be dissolved, a joint oversight committee would monitor the progress of the collaboration, and we would have no further rights to conduct any independent imetelstat development. After an affirmative Continuation Decision by Janssen, the Collaboration Agreement would remain in effect until the expiration of the last‑to‑expire patent or the royalty obligations on sales of imetelstat cease, unless terminated earlier. If Janssen does not effect an affirmative Continuation Decision, then the Collaboration Agreement would terminate and all rights to the imetelstat program would revert to us. Janssen may terminate the Collaboration Agreement at any time for convenience or due to a safety‑related concern. If a notice of termination from Janssen occurs, we would be entitled to certain continued operational support and cost sharing under various circumstances and all rights to the imetelstat program would revert to us. 4. LICENSE AGREEMENTS (Continued) The terms of the Collaboration Agreement contain multiple deliverables, which included at inception: (i) exclusive worldwide rights to develop and commercialize imetelstat for all indications, (ii) transfer of know‑how and intellectual property, including our obligation to procure supply for manufacturing imetelstat for up to nine months after the effective date of the Collaboration Agreement, (iii) participation on the joint committees and working groups and (iv) potential participation in promoting imetelstat in the United States, if approved for commercial sale. We concluded the license for exclusive worldwide rights to develop and commercialize imetelstat has standalone value to Janssen based on the technical and financial resources of Janssen, including Janssen’s drug development experience, sizeable employee base with specific experience in hematologic malignancies, and sufficient capital to independently develop imetelstat on a global basis. Since Janssen has final decision‑making authority in the event a unanimous decision cannot be reached by the joint committees, we determined our participation on the joint committees does not represent a non‑contingent deliverable under the Collaboration Agreement. In addition, we determined our potential participation in promoting imetelstat in the United States does not represent a non‑contingent deliverable because such participation is uncertain and dependent on imetelstat being approved for commercial sale, which is not within our control. Accordingly, we determined delivery of the license rights granted by us to Janssen, together with our performance of certain technology transfer‑related activities under the Collaboration Agreement, represents the sole non‑contingent deliverable under the Collaboration Agreement associated with the upfront payment. Therefore, we accounted for our delivery of the imetelstat license rights and our performance of the technology transfer‑related activities as a single unit of accounting. During the third quarter of 2015, we completed performance of the technology transfer‑related activities to Janssen as outlined under the Collaboration Agreement. Combining this performance with the delivery of the imetelstat license rights, we fully recognized the $35,000,000 upfront payment from Janssen as collaboration revenue on our statements of operations in the third quarter of 2015. We have determined that each of the additional potential milestone payments to us under the Collaboration Agreement, including: (i) the Continuation Fee at the time of an affirmative Continuation Decision, (ii) the Full U.S. Rights Fee, if we do not exercise the U.S. Opt‑In Rights and (iii) payments based on the achievement of certain development, regulatory or sales milestones, represent contingent payments. Consequently, we will recognize revenue for these payments in their entirety upon successful accomplishment of the respective milestone. Royalties on future product sales of imetelstat, if successfully commercialized under the Collaboration Agreement, will be recognized as revenue when earned. Janssen Pharmaceuticals, Inc. License Agreement On September 15, 2016, we entered into the License Agreement with Janssen Pharmaceuticals whereby we granted to Janssen Pharmaceuticals an exclusive worldwide license, or the Exclusive License, under our proprietary patents for the research, development and commercialization of products based on specialized oligonucleotide backbone chemistry and novel amidates for ribonucleic acid interference, or RNAi, for the prevention, treatment and/or diagnosis of any and all human disorders, excluding cancers originating from the blood or bone marrow, and products whose predominant or primary mechanism of action is telomerase inhibition. In addition to the Exclusive License, we granted to Janssen Pharmaceuticals a non‑exclusive worldwide license, or the Non‑Exclusive License, under our patents covering the synthesis of monomers, which are the building blocks of oligonucleotides, and certain know‑how necessary for the research, development and commercialization of products under the Exclusive License. The patent rights under the Non‑Exclusive License are also licensed exclusively to Janssen under the Collaboration Agreement, as described in the section above titled “Janssen Biotech, Inc. Collaboration and License Agreement”, for the development and commercialization of imetelstat, and the License Agreement with Janssen Pharmaceuticals expressly excludes, and is subject to, the rights and licenses granted to Janssen under the Collaboration Agreement. Under the terms of the License Agreement, Janssen Pharmaceuticals, at its sole expense, is required to use reasonable efforts to perform research, development and commercialization activities to obtain at least one licensed product to be researched, developed and commercialized under the License Agreement. We remain responsible for prosecuting the patent rights under the Exclusive License, with reasonable input provided by Janssen Pharmaceuticals, and the costs for such prosecution will be shared between us and Janssen Pharmaceuticals on a 50/50 basis. In addition, we remain responsible for prosecuting the patent rights under the Non‑Exclusive License, as set forth under the terms of the Collaboration Agreement with Janssen. 4. LICENSE AGREEMENTS (Continued) Under the terms of the License Agreement, we received $5,000,000 from Janssen Pharmaceuticals as a non‑refundable upfront payment. We are also eligible to receive additional potential payments of up to an aggregate maximum total of $75,000,000 for the achievement of certain development and regulatory milestones and tiered royalties in the low single digit percentage range on worldwide net sales of each licensed product commercialized under the License Agreement in any countries where there are valid claims under the patent rights licensed to Janssen Pharmaceuticals. The License Agreement will remain in effect until the expiration of the last‑to‑expire patent, unless terminated earlier. Janssen Pharmaceuticals may also terminate the License Agreement at will upon prior written notice to us. In the event of an early termination of the License Agreement, all licenses to Janssen Pharmaceuticals would terminate. The terms of the License Agreement contain multiple deliverables, which included at inception the transfer of: (i) license rights under the Exclusive License and (ii) license rights and certain know‑how under the Non‑Exclusive License. We concluded the License Agreement has standalone value to Janssen Pharmaceuticals based on Janssen Pharmaceuticals’ technical and financial resources, including drug development experience, sizeable employee base with specific knowledge of oligonucleotide chemistry, and sufficient capital to independently research, develop and commercialize products under the License Agreement on a global basis. Accordingly, we have determined delivery of the license rights granted by us to Janssen Pharmaceuticals under the Exclusive License and Non‑Exclusive License, together with the transfer of certain know‑how under the Non‑Exclusive License, represents the sole non‑contingent deliverable under the License Agreement associated with the upfront payment. Therefore, we accounted for our delivery of the license rights and transfer of know‑how under the License Agreement as a single unit of accounting. During the third quarter of 2016, we completed the delivery of the license rights and transfer of know‑how to Janssen Pharmaceuticals under the License Agreement. Accordingly, we fully recognized the $5,000,000 upfront payment from Janssen Pharmaceuticals as license fee revenue on our statements of operations in the third quarter of 2016. We have determined that each of the additional potential development and regulatory milestone payments to us under the License Agreement represent contingent payments. Consequently, we will recognize revenue for these payments in their entirety upon successful accomplishment of the respective milestone. Royalties on potential future product sales under the License Agreement will be recognized as revenue when earned.

ACCRUED LIABILITIES

ACCRUED LIABILITIES	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
ACCRUED LIABILITIES	5. ACCRUED LIABILITIES Accrued liabilities consisted of the following: December 31, (In thousands) 2017 2016 Professional legal and accounting fees $ 272 $ 350 Clinical trial costs 516 723 Other 138 361 $ 926 $ 1,434

RESTRUCTURING

RESTRUCTURING	12 Months Ended
	Dec. 31, 2017
Restructuring And Related Activities [Abstract]
RESTRUCTURING	6. RESTRUCTURING With projected reduced operational demands as a result of the Collaboration Agreement with Janssen, on March 3, 2015, we announced an organizational resizing to reduce our workforce. For the year ended December 31, 2015, we recorded restructuring charges of approximately $1,306,000, net of non‑cash adjustments, related to one‑time termination benefits. These charges included $307,000 of non‑cash stock‑based compensation expense relating to the extension of the post‑termination exercise period for certain stock options previously granted to employees affected by the restructuring. The restructuring resulted in aggregate cash expenditures of approximately $988,000 after adjustments and non‑cash credits. All actions associated with this restructuring were completed in 2015. As of December 31, 2017 and 2016, we had no remaining obligations related to the restructuring.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	7. COMMITMENTS AND CONTINGENCIES Securities Lawsuits We and certain of our officers were named as defendants in two purported class action securities lawsuits filed in the United States District Court for the Northern District of California, or the California District Court, as well as a third securities lawsuit, not styled as a class action, which was originally filed in the United States District Court for the Southern District of Mississippi, but subsequently transferred to the California District Court. These three cases, or the Class Action Lawsuits, which were based on the same factual background, were consolidated for all purposes. On July 21, 2017, the California District Court entered an order and final judgment that dismissed with prejudice and released the claims asserted in the Class Action Lawsuits against all named defendants in connection with the Class Action Lawsuits, including us, and any claims that could have been asserted that arise or relate to the facts alleged in the Class Action Lawsuits, such that every member of the settlement class will be barred from asserting such claims in the future. In connection with the settlement of the Class Action Lawsuits, in April 2017, we paid $250,000 and our insurance providers paid $6,000,000 to a settlement escrow account to be paid to members of the settlement class, less payment of attorneys’ fees and costs to plaintiff’s counsel. The settlement does not constitute any admission of fault or wrongdoing by us or any of the individual defendants. We do not expect to make any additional payments for and do not expect, and are not aware of, any additional claims arising from or related to the facts alleged in the Class Action Lawsuits and asserted by stockholders who have opted out of the settlement class in the Class Action Lawsuits. However, it is possible that additional lawsuits may be filed, or allegations may be made by stockholders, with respect to these same or other matters and also naming us and/or our officers and directors as defendants. Monitoring, initiating and defending against legal actions is time-consuming for our management, is likely to be expensive and may detract from our ability to fully focus our internal resources on our business activities. In addition, despite the availability of insurance, we may incur substantial legal fees and costs in connection with any additional litigation and such amounts could be material to our financial statements. We may expend significant resources in the settlement or defense of any additional lawsuits, and we may not prevail in such lawsuits. We have not established any reserve for any potential liability relating to any additional lawsuits. Indemnifications to Officers and Directors Our corporate bylaws require that we indemnify our officers and directors, as well as those who act as directors and officers of other entities at our request, against expenses, judgments, fines, settlements and other amounts actually and reasonably incurred in connection with any proceedings arising out of their services to Geron. In addition, we have entered into separate indemnification agreements with each of our directors and officers which provide for indemnification of these directors and officers under similar circumstances and under additional circumstances. The indemnification obligations are more fully described in our bylaws and the indemnification agreements. We purchase standard insurance to cover claims or a portion of the claims made against our directors and officers. Since a maximum obligation is not explicitly stated in our bylaws or in our indemnification agreements and will depend on the facts and circumstances that arise out of any future claims, the overall maximum amount of the obligations cannot be reasonably estimated. Operating Lease Commitment On September 21, 2017, we amended the lease agreement for our premises at 149 Commonwealth Drive, Menlo Park, California, to extend the lease term from February 2018 through January 2020. As of December 31, 2017, operating lease obligations under the amended lease agreement include aggregate future minimum payments of approximately $1,435,000, of which payments of approximately $678,000, $699,000 and $58,000 are due in 2018, 2019 and 2020, respectively. Rent expense under our operating leases was approximately $691,000, $708,000 and $878,000 for the years ended December 31, 2017, 2016 and 2015, respectively. 7. COMMITMENTS AND CONTINGENCIES (Continued) Severance Plan We have an Amended and Restated Severance Plan, or Severance Plan, that applies to all employees that are not subject to performance improvement plans, and provides for, among other benefits: (i) a severance payment upon a Change of Control Triggering Event and Separation from Service and (ii) a severance payment for each non‑executive employee upon a Non‑Change of Control Triggering Event and Separation from Service. As defined in the Severance Plan, a Change of Control Triggering Event and Separation from Service requires a “double trigger” where: (i) an employee is terminated by us without cause in connection with a change of control or within 12 months following a change of control provided, however, that if an employee is terminated by us in connection with a change of control but immediately accepts employment with our successor or acquirer, the employee will not be eligible for the benefits outlined in the Severance Plan, (ii) an employee resigns because in connection with a change of control, the offered terms of employment (new or continuing) by us or our successor or acquirer within 30 days after the change of control results in a material change in the terms of employment, or (iii) after accepting (or continuing) employment with us after a change of control, an employee resigns within 12 months following a change of control due to a material change in the terms of employment. Under the Severance Plan, a Non‑Change of Control Triggering Event and Separation from Service is defined as an event where a non‑executive employee is terminated by us without cause. Severance payments range from two to 18 months of base salary, depending on the employee’s position with us, payable in a lump sum payment. The Severance Plan also provides that the provisions of employment agreements entered into between us and executive or non‑executive employees supersede the provisions of the Severance Plan. As of December 31, 2017, all our executive officers have employment agreements with provisions that may provide greater severance benefits than those in the Severance Plan.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2017
Stockholders Equity Note [Abstract]
STOCKHOLDERS' EQUITY	8. STOCKHOLDERS’ EQUITY Sales Agreement On August 28, 2015, we entered into an At Market Issuance Sales Agreement, or the 2015 Sales Agreement, with MLV & Co. LLC, or MLV, pursuant to which we may elect to issue and sell shares of our common stock having an aggregate offering price of up to $50,000,000 from time to time into the open market at prevailing prices through MLV as our sales agent. We will pay MLV an aggregate commission rate equal to up to 3.0% of the gross proceeds of the sales price per share for common stock sold through MLV under the 2015 Sales Agreement. Pursuant to the 2015 Sales Agreement, sales of common stock will be made in such quantities and on such minimum price terms as we may set from time to time. We are not obligated to make any sales of common stock under the 2015 Sales Agreement. In December 2017, we sold an aggregate of 614,230 shares of our common stock pursuant to the 2015 Sales Agreement, resulting in net cash proceeds of approximately $1,060,000 after deducting sales commissions and offering expenses payable by us. The 2015 Sales Agreement will expire in August 2018 unless extended by the parties. Warrants In connection with each disbursement under a previous loan agreement with the California Institute for Regenerative Medicine, or CIRM, we were obligated to issue to CIRM a warrant to purchase Geron common stock. Such warrants and the underlying common stock were unregistered. We have no further obligations to issue any additional warrants to CIRM. As of December 31, 2017, a warrant to purchase 537,893 shares of our common stock remained outstanding. The warrant was issued to CIRM in August 2011 at an exercise price of $3.98 per share and expires in August 2021. On March 31, 2015, a warrant to purchase 235,000 shares of our common stock was exercised at an exercise price of $3.75 per share. We received cash proceeds of approximately $881,000 from the exercise of this warrant. 8. STOCKHOLDERS’ EQUITY (Continued) Equity Plans 2002 Equity Incentive Plan The 2002 Equity Incentive Plan, or 2002 Plan, expired in May 2012. Upon the adoption of the 2011 Incentive Award Plan in May 2011 (see below), no further grants of options or stock purchase rights were made from the 2002 Plan. Options granted under the 2002 Plan expire no later than ten years from the date of grant. Option exercise prices were equal to 100% of the fair market value of the underlying common stock on the date of grant. Service‑based stock options under the 2002 Plan generally vested over a period of four years from the date of the option grant. Other stock awards (restricted stock awards and restricted stock units) had variable vesting schedules which were determined by our board of directors on the date of grant. All outstanding awards granted under the 2002 Plan remain subject to the terms of the 2002 Plan and the individual award agreements thereunder. 2011 Incentive Award Plan In May 2011, our stockholders approved the adoption of the 2011 Incentive Award Plan, or 2011 Plan. Our board of directors administers the 2011 Plan. The 2011 Plan provides for grants of either incentive stock options or nonstatutory stock options and stock purchase rights to employees (including officers and employee directors) and consultants (including non‑employee directors). As of December 31, 2017, an aggregate of 6,202,727 shares of our common stock were available for future grants of equity awards under the 2011 Plan. Pursuant to the terms of the 2011 Plan, any shares subject to outstanding stock options or outstanding unvested restricted stock awards originally granted under the 2002 Plan that expire or terminate for any reason prior to exercise or settlement or are forfeited because of the failure to meet a contingency or condition required to vest such shares shall become available for issuance under the 2011 Plan. Options granted under the 2011 Plan expire no later than ten years from the date of grant. Option exercise prices shall be equal to the fair market value of the underlying common stock on the date of grant. If, at the time we grant an option, the optionee directly or by attribution owns stock possessing more than 10% of the total combined voting power of all classes of our stock, the option exercise price shall be at least 110% of the fair market value of the underlying common stock and shall not be exercisable more than five years after the date of grant. We grant service‑based stock options to employees under our 2011 Plan that generally vest over a period of four years from the date of the option grant. Other stock awards (restricted stock awards and restricted stock units) have variable vesting schedules as determined by our board of directors on the date of grant. Under certain circumstances, options may be exercised prior to vesting, subject to our right to repurchase shares subject to such option at the exercise price paid per share. Our repurchase rights would generally terminate on a vesting schedule identical to the vesting schedule of the exercised option. During 2017, we have not repurchased any shares under the 2011 Plan. As of December 31, 2017, we have no shares outstanding subject to repurchase. As of December 31, 2017, our Non‑Employee Director Compensation Policy adopted by our board of directors in March 2014 and amended by our board of directors in February 2015, May 2015 and February 2016 provides for the automatic grant to non‑employee directors of the following types of equity awards under the 2011 Plan: First Director Option. Each person who becomes a non‑employee director, whether by election by our stockholders or by appointment by our board of directors to fill a vacancy, will automatically be granted an option to purchase 100,000 shares of common stock, or First Director Option, on the date such person first becomes a non‑employee director. The First Director Option vests annually over three years upon each anniversary date of appointment to our board of directors. Subsequent Director Option. Each non‑employee director (other than any director receiving a First Director Option on the date of the annual meeting) will automatically be granted a subsequent option to purchase 50,000 shares of common stock, a Subsequent Director Option, on the date of the annual meeting of stockholders in each year during such director’s service on our board of directors. The Subsequent Director Option vests in full on the earlier of: (i) the date of the next annual meeting of our stockholders or (ii) the first anniversary of the date of grant. 8. STOCKHOLDERS’ EQUITY (Continued) 2006 Directors’ Stock Option Plan The 2006 Directors’ Stock Option Plan, or 2006 Directors Plan, was terminated by our board of directors and replaced by the 2011 Plan in March 2014. No further grants of options were made from the 2006 Directors Plan upon the 2006 Directors Plan’s termination. All outstanding awards granted under the 2006 Directors Plan remain subject to the terms of the 2006 Directors Plan and the individual award agreements made thereunder. The options granted to non‑employee directors under the 2006 Directors Plan were nonstatutory stock options, and they expire no later than ten years from the date of grant. The option exercise price was equal to the fair market value of the underlying common stock on the date of grant. The First Director Option granted to non‑employee directors under the 2006 Directors Plan vested annually over three years upon each anniversary date of appointment to the board of directors. The Subsequent Director Option granted to non‑employee directors on the date of the annual meeting of stockholders in each year during such director’s service on our board of directors under the 2006 Directors Plan vested one year from the date of grant. Aggregate option and award activity for the 2002 Plan, 2011 Plan and 2006 Directors Plan is as follows: Outstanding Options Weighted Average Aggregate Shares Weighted Average Remaining Intrinsic Available Number of Exercise Price Contractual Life Value For Grant Shares Per Share (In years) (In thousands) Balance at December 31, 2016 9,570,535 19,125,287 $ 3.15 Options granted (3,484,000 ) 3,484,000 $ 2.19 Awards granted (72,066 ) — $ — Options exercised — (12,500 ) $ 1.41 Options cancelled/forfeited 188,258 (188,258 ) $ 7.99 Balance at December 31, 2017 6,202,727 22,408,529 $ 2.96 6.24 $ 2,034 Options exercisable at December 31, 2017 17,249,032 $ 3.03 5.57 $ 2,034 Options fully vested and expected to vest at December 31, 2017 22,171,142 $ 2.96 6.21 $ 2,034 The aggregate intrinsic value in the preceding table represents the total intrinsic value, based on Geron’s closing stock price of $1.80 per share as of December 29, 2017, which would have been received by the option holders had all the option holders exercised their options as of that date. We have not granted any options with an exercise price below or greater than the fair market value of our common stock on the date of grant in 2017, 2016 or 2015. As of December 31, 2017, 2016 and 2015, there were 17,249,032, 14,074,457 and 11,356,232 exercisable options outstanding at weighted average exercise prices per share of $3.03, $2.99 and $2.98, respectively. The total pretax intrinsic value of stock options exercised during 2017, 2016 and 2015 was $15,000, $595,000 and $2,398,000, respectively. Cash received from the exercise of options in 2017, 2016 and 2015 totaled approximately $18,000, $493,000 and $2,205,000, respectively. 8. STOCKHOLDERS’ EQUITY (Continued) Information about stock options outstanding as of December 31, 2017 is as follows: Options Outstanding Weighted Average Weighted Average Remaining Number of Exercise Price Contractual Life Exercise Price Range Shares Per Share (In years) $1.10 - $1.51 5,655,662 $ 1.45 4.89 $1.55 - $2.16 5,631,031 $ 2.08 7.04 $2.22 - $4.34 6,000,783 $ 3.37 7.60 $4.42 - $7.31 5,121,053 $ 5.10 5.27 $1.10 - $7.31 22,408,529 $ 2.96 6.24 Aggregate restricted stock activity for the 2011 Plan is as follows: Weighted Average Weighted Average Grant Date Remaining Number of Fair Value Contractual Term Shares Per Share (In years) Non-vested restricted stock at December 31, 2016 — $ — — Granted 72,066 $ 2.20 Vested (72,066 ) $ 2.20 Non-vested restricted stock at December 31, 2017 — $ — — The weighted average grant date fair value of restricted stock granted during the years ended December 31, 2017, 2016 and 2015 was $2.20, $2.44 and $3.75 per share, respectively. The total fair value of restricted stock that vested during 2017, 2016 and 2015 was $159,000, $54,000 and $275,000, respectively. Employee Stock Purchase Plan In March 2014, our board of directors adopted the 2014 Employee Stock Purchase Plan, or 2014 Purchase Plan. The 2014 Purchase Plan was approved by our stockholders in May 2014. The 2014 Purchase Plan replaced the 1996 Employee Stock Purchase Plan, or 1996 Purchase Plan, which was terminated effective as of the date the 2014 Purchase Plan was approved by our stockholders. Under the 2014 Purchase Plan, we are authorized to sell to eligible employees up to an aggregate of 1,000,000 shares of Geron common stock. As of December 31, 2017, an aggregate of 104,692 shares of our common stock have been issued under the 2014 Purchase Plan since its adoption. The 2014 Purchase Plan is comprised of a series of offering periods, each with a maximum duration (not to exceed 12 months) with new offering periods commencing on January 1st and July 1st of each year. The date an employee enters the offering period will be designated as the entry date for purposes of that offering period. An employee may participate only in one offering period at a time. Each offering period consists of two consecutive purchase periods of six months’ duration, with the last day of such period designated a purchase date. Under the terms of the 2014 Purchase Plan, employees can choose to have up to 10% of their annual salary withheld to purchase our common stock. An employee may not make additional payments into such account or increase the withholding percentage during the offering period. The purchase price per share at which common stock is purchased by the employee on each purchase date within the offering period is equal to 85% of the lower of (i) the fair market value per share of Geron common stock on the employee’s entry date into that offering period or (ii) the fair market value per share of Geron common stock on the purchase date. If the fair market value per share of Geron common stock on the purchase date is less than the fair market value at the beginning of the offering period, a new 12 month offering period will automatically begin on the first business day following the purchase date with a new fair market value. 8. STOCKHOLDERS’ EQUITY (Continued) Stock‑Based Compensation for Employees and Directors We measure and recognize compensation expense for all share‑based payment awards made to employees and directors, including employee stock options, restricted stock awards and employee stock purchases, based on grant‑date fair values for these instruments. We use the Black Scholes option‑pricing model to estimate the grant‑date fair value of our stock options and employee stock purchases. The fair value for service‑based restricted stock awards is determined using the fair value of our common stock on the date of grant. As stock‑based compensation expense recognized in the statements of operations for the years ended December 31, 2017, 2016 and 2015 is based on awards ultimately expected to vest, it has been reduced for estimated forfeitures but at a minimum, reflects the grant‑date fair value of those awards that actually vested in the period. Forfeitures have been estimated at the time of grant based on historical data and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. With the adoption of Accounting Standards Update No. 2016-09, Improvements to Employee Share Based Payment Accounting We recognize stock‑based compensation expense on a straight‑line basis over the requisite service period, which is generally the vesting period. The following table summarizes the stock‑based compensation expense related to stock options, restricted stock awards and employee stock purchases for the years ended December 31, 2017, 2016 and 2015 which was allocated as follows: Year Ended December 31, (In thousands) 2017 2016 2015 Research and development $ 988 $ 1,275 $ 2,139 Restructuring charges — — 307 General and administrative 7,156 6,970 5,951 Stock-based compensation expense included in operating expenses $ 8,144 $ 8,245 $ 8,397 Stock‑based compensation expense also has been recognized for the modification of the post‑termination exercise period for certain stock options previously granted to employees affected by the March 2015 restructuring, which has been included in restructuring charges in our statements of operations. See Note 6 on Restructuring for further discussion of the restructuring. The fair value of stock options granted in 2017, 2016 and 2015 has been estimated at the date of grant using the Black Scholes option‑pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Dividend yield 0% 0% 0% Expected volatility range 0.884 to 0.892 0.888 to 0.890 0.874 to 0.884 Risk-free interest rate range 1.98% to 1.99% 1.21% to 1.38% 1.68% to 1.71% Expected term 5.5 yrs 5.5 yrs 5.5 yrs 8. STOCKHOLDERS’ EQUITY (Continued) The fair value of employee stock purchases in 2017, 2016 and 2015 has been estimated using the Black Scholes option‑pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Dividend yield 0% 0% 0% Expected volatility range 0.577 to 0.641 0.641 to 0.684 0.654 to 1.392 Risk-free interest rate range 0.45% to 0.89% 0.28% to 0.45% 0.11% to 0.28% Expected term range 6 - 12 mos 6 - 12 mos 6 - 12 mos Dividend yield is based on historical cash dividend payments and Geron has paid no cash dividends to date. The expected volatility range is based on historical volatilities of our stock since traded options on Geron common stock do not correspond to option terms and the trading volume of options is limited. The risk‑free interest rate range is based on the U.S. Zero Coupon Treasury Strip Yields for the expected term in effect on the date of grant for an award. The expected term of options is derived from actual historical exercise and post‑vesting cancellation data and represents the period of time that options granted are expected to be outstanding. The expected term of employees’ purchase rights is equal to the purchase period. Based on the Black Scholes option‑pricing model, the weighted average estimated fair value of stock options granted during the years ended December 31, 2017, 2016 and 2015 was $1.58, $1.83 and $3.06 per share, respectively. The weighted average estimated fair value of employees’ purchase rights for the years ended December 31, 2017, 2016 and 2015 was $0.75, $1.01 and $1.64 per share, respectively. As of December 31, 2017, total compensation cost related to unvested share‑based payment awards not yet recognized, net of estimated forfeitures, was $8,008,000, which is expected to be recognized over the next 26 months on a weighted‑average basis. 401(k) Plan Matching Contributions We sponsor a defined‑contribution savings plan under Section 401(k) of the Internal Revenue Code covering all full‑time U.S. employees, or the Geron 401K Plan. Participating employees may contribute up to the annual Internal Revenue Service contribution limit. The Geron 401K Plan also permits us to provide discretionary matching and profit sharing contributions. Prior to 2014, our board of directors approved matching contributions for the Geron 401K Plan in our common stock, which vested ratably over four years for each year of service completed by our employees, commencing from the date of hire. Stock‑Based Compensation to Service Providers We grant stock options and restricted stock awards to consultants from time to time in exchange for services performed for us. In general, the stock options and restricted stock awards vest over the contractual period of the consulting arrangement. The fair value of stock options and restricted stock awards held by consultants is recorded as operating expenses over the vesting term of the respective equity awards. In addition, we will record any increase in the fair value of the stock options and restricted stock awards as the respective equity award vests. We recorded stock‑based compensation expense of $41,000, $104,000 and $311,000 for the vested portion of the fair value of stock options and restricted stock awards held by consultants in 2017, 2016 and 2015, respectively. We have also issued common stock to non‑employee directors and consultants. For stock issuances where services are to be performed for us, we record a prepaid asset equal to the fair market value of the shares on the date of issuance and amortize the fair value of the shares to our operating expenses on a pro‑rata basis as services are performed. For stock issuances where services have been performed for us, we record the fair market value of the shares on the date of issuance to offset the amounts owed. In 2017, 2016 and 2015, we issued 72,066, 21,541 and 18,077 shares of common stock, respectively, in exchange for services provided. In 2017, 2016 and 2015, we recognized approximately $159,000, $52,000 and $53,000, respectively, of expense in connection with stock grants to non‑employee directors and consultants. 8. STOCKHOLDERS’ EQUITY (Continued) Common Stock Reserved for Future Issuance Common stock reserved for future issuance as of December 31, 2017 is as follows: Outstanding stock options 22,408,529 Options and awards available for grant 6,202,727 Employee stock purchase plan 895,308 Warrant outstanding 537,893 Total 30,044,457

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	9. INCOME TAXES Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred tax assets are as follows: December 31, 2017 2016 (In thousands) Net operating loss carryforwards $ 187,700 $ 280,400 Research credits 34,300 29,800 Capitalized research and development 2,500 300 License fees 100 200 Other-net 8,200 11,500 Total deferred tax assets 232,800 322,200 Valuation allowance for deferred tax assets (232,800 ) (322,200 ) Net deferred tax assets $ — $ — We record net deferred tax assets to the extent we believe these assets will more likely than not be realized. In making such determination, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies and recent financial performance. Forming a conclusion that a valuation allowance is not required is difficult when there is negative evidence such as cumulative losses in recent years. Because of our history of losses, the net deferred tax assets have been fully offset by a valuation allowance. The valuation allowance decreased by $89,400,000 and $2,300,000 for the years ended December 31, 2017 and 2015, respectively, and increased by $9,600,000 during the year ended December 31, 2016. No income tax benefit was realized from stock options exercised in 2017. As of December 31, 2017, we had domestic federal net operating loss carryforwards of approximately $793,900,000 expiring at various dates beginning in 2018 through 2037 and state net operating loss carryforwards of approximately $300,200,000 expiring at various dates beginning in 2017 through 2037, if not utilized. We also had federal research and development tax credit carryforwards of approximately $34,000,000 expiring at various dates beginning in 2018 through 2037, if not utilized. Our state research and development tax credit carryforwards of approximately $19,100,000 carry forward indefinitely. Due to the change of ownership provisions of the Tax Reform Act of 1986, utilization of a portion of our domestic net operating loss and tax credit carryforwards may be limited in future periods. Further, a portion of the carryforwards may expire before being applied to reduce future income tax liabilities. 9. INCOME TAXES (Continued) On December 22, 2017, the Tax Cuts and Jobs Act of 2017, or 2017 Tax Act, was signed into law. Among other things, the 2017 Tax Act permanently lowers the corporate federal income tax rate to 21% from the existing maximum rate of 35%, effective for tax years including or commencing January 1, 2018. In accordance with GAAP, we remeasured the carrying value of our deferred tax assets as of December 31, 2017 using the new enacted corporate federal income tax rate of 21%. This remeasurement reduced our aggregate deferred tax assets and correspondingly reduced the valuation allowance by approximately $102,300,000. The remeasurement did not impact our financial statements. In accordance with Staff Accounting Bulletin 118, as of December 31, 2017, we have made a reasonable estimate of the effects of the 2017 Tax Act on our existing deferred tax assets. Our preliminary estimate and the remeasurement of our deferred tax assets are subject to further analysis related to certain matters, such as developing interpretations of the provisions of the 2017 Tax Act, changes to certain estimates and the filing of our tax returns. U.S. Treasury regulations, administrative interpretations or court decisions interpreting the 2017 Tax Act may require further adjustments and changes in our estimates. The final determination of the 2017 Tax Act and the remeasurement of our deferred assets will be completed as additional information becomes available, but we expect no later than one year from the enactment of the 2017 Tax Act. We adopted the provision of the standard for accounting for uncertainties in income taxes on January 1, 2007. Upon adoption, we recognized no material adjustment in the liability for unrecognized tax benefits. At December 31, 2017, we had approximately $15,900,000 of unrecognized tax benefits, none of which would currently affect our effective tax rate if recognized due to our deferred tax assets being fully offset by a valuation allowance. A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands): Balance as of December 31, 2016 $ 14,700 Increase related to current year tax positions 1,200 Balance as of December 31, 2017 $ 15,900 If applicable, we would classify interest and penalties related to uncertain tax positions in income tax expense. Through December 31, 2017, there has been no interest expense or penalties related to unrecognized tax benefits. We do not currently expect any significant changes to unrecognized tax benefits during the fiscal year ended December 31, 2018. In certain cases, our uncertain tax positions are related to tax years that remain subject to examination by the relevant tax authorities. Tax years for which we have carryforward net operating loss and credit attributes remain subject to examination by federal and most state tax authorities.

STATEMENTS OF CASH FLOWS DATA

STATEMENTS OF CASH FLOWS DATA	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
STATEMENTS OF CASH FLOWS DATA	10. STATEMENTS OF CASH FLOWS DATA Year Ended December 31, 2017 2016 2015 (In thousands) Supplemental investing activities: Net unrealized (loss) gain on marketable securities $ (154 ) $ 160 $ (129 ) We have not made any cash payments for taxes or interest for the years ended December 31, 2017, 2016 and 2015.

SELECTED QUARTERLY FINANCIAL IN

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)	11. SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) First Second Third Fourth Quarter Quarter Quarter Quarter (In thousands, except per share amounts) Year Ended December 31, 2017: Revenues $ 537 $ 174 $ 163 $ 191 Operating expenses 8,031 6,905 7,407 7,977 Net loss (7,183 ) (6,405 ) (6,899 ) (7,429 ) Basic and diluted net loss per share $ (0.05 ) $ (0.04 ) $ (0.04 ) $ (0.05 ) Year Ended December 31, 2016: Revenues ( 1) $ 749 $ 211 $ 5,108 $ 94 Operating expenses 9,826 9,122 8,985 8,875 Net loss (8,842 ) (8,637 ) (3,576 ) (8,482 ) Basic and diluted net loss per share $ (0.06 ) $ (0.05 ) $ (0.02 ) $ (0.05 ) (1) The third quarter of 2016 includes the full recognition of the $5,000,000 upfront payment from Janssen Pharmaceuticals as license fee revenue. See Note 4 on License Agreements. Basic and diluted net loss per share are computed independently for each of the quarters presented. Therefore, the sum of the quarters may not be equal to the full year net loss per share amounts.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENT	12. SUBSEQUENT EVENT In January

ORGANIZATION AND SUMMARY OF S21

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing net income (loss) by the weighted‑average number of shares of common stock outstanding during the periods presented, without consideration for potential common shares. Diluted net income per share is calculated by adjusting the weighted‑average number of shares of common stock outstanding for the dilutive effect of potential common shares outstanding for the periods presented, as determined using the treasury‑stock method. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase our common stock. For periods in which we have incurred a net loss, potential common shares outstanding for the periods presented, as determined using the treasury‑stock method, are excluded, as their effect would be anti‑dilutive, resulting in the same number of shares being used for the calculation of basic and diluted net loss per share. For all periods presented in the accompanying statements of operations, the net income (loss) applicable to common stockholders is equal to the reported net income (loss). Year Ended December 31, (In thousands, except share and per share data) 2017 2016 2015 Net (loss) income $ (27,916 ) $ (29,537 ) $ 46 Weighted-average shares: Basic 159,224,986 159,045,644 158,036,162 Effect of dilutive securities: Stock options and restricted stock awards — — 4,627,732 Diluted 159,224,986 159,045,644 162,663,894 Net (loss) income per share: Basic $ (0.18 ) $ (0.19 ) $ 0.00 Diluted $ (0.18 ) $ (0.19 ) $ 0.00 Because we were in a net loss position for 2017 and 2016, 2,389,310 and 3,023,520 potential common shares, respectively, related to outstanding stock options and restricted stock awards (as determined using the treasury‑stock method at the estimated average market value) were excluded from the diluted net loss per share calculation as their effect would have been anti‑dilutive. In addition for 2017, 2016 and 2015, 14,475,616, 11,352,766 and 9,375,851 potentially dilutive securities, respectively, were excluded from the treasury‑stock method and calculation of diluted net income (loss) per share as their effect would have been anti‑dilutive.
Use of Estimates	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) Use of Estimates The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, we evaluate our estimates, including those related to accrued liabilities, revenue recognition, fair value of marketable securities, income taxes, and stock-based compensation. We base our estimates on historical experience and on various other market specific and relevant assumptions that we believe to be reasonable under the circumstances. Actual results could differ from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Cash Equivalents and Marketable Securities We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents. We are subject to credit risk related to our cash equivalents and marketable securities. We place our cash and cash equivalents in money market funds, commercial paper, corporate notes and cash operating accounts. Our marketable securities include U.S. government‑sponsored enterprise securities, commercial paper and corporate notes. We classify our marketable securities as available‑for‑sale. We record available‑for‑sale securities at fair value with unrealized gains and losses reported in accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included in interest and other income and are derived using the specific identification method for determining the cost of securities sold and have been insignificant to date. Dividend and interest income are recognized when earned and included in interest and other income in our statements of operations. We recognize a charge when the declines in the fair values below the amortized cost basis of our available‑for‑sale securities are judged to be other‑than‑temporary. We consider various factors in determining whether to recognize an other‑than‑temporary charge, including whether we intend to sell the security or whether it is more likely than not that we would be required to sell the security before recovery of the amortized cost basis. Declines in market value judged as other‑than‑temporary result in a charge to interest and other income. We have not recorded any other‑than‑temporary impairment charges on our available‑for‑sale securities for the years ended December 31, 2017, 2016 and 2015. See Note 2 on Fair Value Measurements. Cost Method Investments We use the cost method of accounting for non-marketable equity securities where our ownership represents less than 20% of such entity, and we cannot exert significant influence over its operations. These securities are carried at cost and adjusted for impairments. Fair Value of Derivatives Non‑employee options classified as derivative liabilities are marked to fair value at each financial reporting date with any resulting changes in fair value being recorded in the statements of operations as unrealized gain (loss) on derivatives. The non‑employee options continue to be reported as a derivative liability until such time as the instruments are exercised or expire, at which time these instruments are marked to fair value and reclassified from liabilities to stockholders’ equity. As of March 31, 2015, all non‑employee options classified as derivative liabilities expired unexercised.
Revenue Recognition	Revenue Recognition We recognize revenue for each unit of accounting when all of the following criteria have been met: (a) persuasive evidence of an arrangement exists, (b) delivery has occurred or services have been rendered, (c) the seller’s price to the buyer is fixed or determinable, and (d) collectability is reasonably assured. Amounts received prior to satisfying these revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as noncurrent deferred revenue. License and/or Collaboration Agreements In addition to the Collaboration Agreement (which is more fully described in Note 4 on License Agreements), we have entered into several license or collaboration agreements with various oncology, diagnostics, research tools and biologics production companies. Economic terms in these agreements may include non‑refundable upfront license payments in cash or equity securities, option payments in cash or equity securities, cost reimbursements, cost‑sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. In applying the appropriate revenue recognition guidance related to these agreements, we first assess whether the arrangement contains multiple elements. In this evaluation, we consider: (i) the deliverables included in the arrangement and (ii) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires us to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in our control. In assessing whether an item has standalone value, we consider factors such as the research, manufacturing and commercialization capabilities of the collaboration partner or licensee and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner or licensee can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. We then apply the applicable revenue recognition criteria noted above to each of the separate units of accounting in determining the appropriate period and pattern of recognition. We determine how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under relevant accounting guidance. The estimated fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor‑specific‑objective evidence and third‑party evidence are not available. Upfront non‑refundable signing, license or non‑exclusive option fees are recognized as revenue: (i) when rights to use the intellectual property have been delivered, if the license has standalone value from the other deliverables to be provided under the agreement, or (ii) over the term of the agreement if we have continuing performance obligations, as the arrangement would be accounted for as a single unit of accounting. When payments are received in equity securities, we do not recognize any revenue unless such securities are determined to be realizable in cash. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either (1) our performance to achieve the milestone or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms (including other potential milestone consideration) within the arrangement. We consider various factors, such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone, in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestone payments for milestones that are considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestone payments for milestones that are not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met. Our license and collaboration agreements with certain partners also provide for contingent payments to us based solely upon the performance of the respective partner. For such contingent amounts, we recognize the payments as revenue when earned under the applicable contract, which is generally upon completion of performance by the respective partner, provided that collection is reasonably assured. Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collection is reasonably assured. If royalties cannot be reasonably estimated or collection of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments is accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met and we have no performance obligations related to the milestone. Cost‑sharing expenses are recorded as earned or owed based on the performance requirements by both parties under the respective contracts. For arrangements in which we and our collaboration partner in the agreement are exposed to significant risks and rewards that depend on the commercial success of the activity, we recognize payments between the parties on a net basis and record such amounts as a reduction or addition to research and development expense. For arrangements in which we have agreed to perform certain research and development services for our collaboration partner and are not exposed to significant risks and rewards that depend on the commercial success of the activity, we recognize the respective cost reimbursements as revenue under the collaborative agreement as the related research and development services are rendered.
Restricted Cash	Restricted Cash Restricted cash consists of funds maintained in a separate certificate of deposit account for credit card purchases.
Research and Development Expenses	Research and Development Expenses Research and development expenses consist of expenses incurred in identifying, developing and testing product candidates resulting from our independent efforts as well as efforts associated with collaborations. These expenses include, but are not limited to, in‑process research and development acquired in an asset acquisition and deemed to have no alternative future use, payroll and personnel expense, lab supplies, preclinical studies, clinical trials, including support for investigator‑sponsored clinical trials, raw materials to manufacture clinical trial drugs, manufacturing costs for research and clinical trial materials, sponsored research at other labs, consulting, costs to maintain technology licenses, our proportionate share of research and development costs under cost‑sharing arrangements with collaboration partners and research‑related overhead. Research and development costs are expensed as incurred, including costs incurred under our collaboration and/or license agreements. 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) For the clinical development activities being conducted by Janssen under the Collaboration Agreement, we monitor patient enrollment levels and related activities to the extent possible through discussions with Janssen personnel and base our estimates on the best information available at the time. However, additional information may become available to us which would allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain.
Depreciation and Amortization	Depreciation and Amortization We record property and equipment at cost and calculate depreciation using the straight‑line method over the estimated useful lives of the assets, generally four years. Leasehold improvements are amortized over the shorter of the estimated useful life or remaining term of the lease.
Stock-Based Compensation	Stock‑Based Compensation We maintain various stock incentive plans under which stock options and restricted stock awards are granted to employees, directors and consultants. We also have an employee stock purchase plan for all eligible employees. We recognize stock‑based compensation expense based on the grant-date fair values of these instruments on a straight‑line basis over the requisite service period, which is generally the vesting period. The determination of grant-date fair values for our stock options and employee stock purchases using the Black Scholes option‑pricing model is affected by our stock price as well as assumptions regarding a number of complex and subjective variables. The grant-date fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. For our non‑employee stock‑based awards, the measurement date on which the fair value of the stock‑based award is calculated is equal to the earlier of: (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. We recognize stock‑based compensation expense for the fair value of the vested portion of non‑employee stock‑based awards in our statements of operations. For additional information, see Note 8 on Stockholders’ Equity.
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Accumulated other comprehensive loss includes certain changes in stockholders’ equity which are excluded from net income (loss). Accumulated other comprehensive loss on our balance sheets as of December 31, 2017 and 2016 is solely comprised of net unrealized losses on marketable securities.
Income Taxes	Income Taxes We maintain deferred tax assets and liabilities that reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and are subject to tests of recoverability. Our deferred tax assets include net operating loss carryforwards, research credits and capitalized research and development. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. Our net deferred tax asset has been fully offset by a valuation allowance because of our history of losses. Any potential accrued interest and penalties related to unrecognized tax benefits would be recorded as income tax expense.
Concentrations of Customers and Suppliers	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) Concentrations of Customers and Suppliers The majority of our revenues was earned in the United States. Two customers accounted for approximately 39% of our 2017 revenues. Approximately 81% of our 2016 revenues represented an upfront payment from Janssen Pharmaceuticals, Inc., or Janssen Pharmaceuticals, in connection with a license agreement signed in September 2016, or the License Agreement. Approximately 96% of our 2015 revenues represented an upfront payment from Janssen under the imetelstat Collaboration Agreement. In accordance with the Collaboration Agreement, Janssen is now responsible for the manufacture and management of the supply of imetelstat on a global basis for clinical trials and, after any regulatory approval, all commercial activities. Janssen contracts third‑party manufacturers to produce GMP‑grade drugs for preclinical and clinical studies. Janssen also contracts for starting materials to supply those manufacturers and for its own use. Certain development and clinical activities may be delayed if Janssen is unable to obtain sufficient quantities of starting materials or GMP‑grade drugs from current third‑party suppliers or other third‑party sources.
Segment Information	Segment Information Our executive management team represents our chief decision maker. We view our operations as a single segment, the development of therapeutic products for oncology. As a result, the financial information disclosed herein materially represents all of the financial information related to our principal operating segment.
Recent Accounting Pronouncements Not Yet Effective	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update No. 2014-09, or ASU 2014-09, which created Accounting Standards Codification Topic 606, Revenue from Contracts with Customers Revenue Recognition Revenue From Contracts With Customers: Principal vs. Agent Considerations Revenue From Contracts with Customers: Identifying Performance Obligations and Licensing Revenue From Contracts with Customers: Narrow-Scope Improvements and Practical Expedients Revenue from Contracts with Customers Technical Corrections and Improvements to Topic 606, The new revenue standard is principles-based and the interpretation of those principles may vary from company to company based on their unique circumstances. It is possible that interpretations, industry practice, and guidance may evolve as companies and the accounting profession work to implement this new standard. We have assessed the differences in accounting for our existing contracts under the new guidance compared to current revenue accounting standards. We have not identified any material differences in the accounting treatment under ASU 2014-09 compared to the current accounting treatment for the Collaboration Agreement with Janssen and the License Agreement with Janssen Pharmaceuticals, which are our most significant license agreements. With the adoption of ASU 2014-09, we expect royalty revenues from product sales by licensees of our human telomerase reverse transcriptase, or hTERT, technology and cell-based research products to be recognized earlier than under our current accounting policy for revenue recognition. Accordingly, we expect to record a one-time cumulative catch-up adjustment in 2018 to reflect 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Continued) estimated royalty revenues on product sales earned in 2017 for which payments have not yet been received. We do not expect that the adoption of ASU 2014-09 will have a material impact on our financial statements and related disclosures. In January 2016, the FASB issued Accounting Standards Update No. 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) In August 2016, the FASB issued Accounting Standards Update No. 2016-15, Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued Accounting Standards Update No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash In May 2017, the FASB issued Accounting Standards Update No. 2017-09, Compensation — Stock Compensation: Scope of Modification Accounting

ORGANIZATION AND SUMMARY OF S22

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of the calculation of basic and diluted net (loss) income per share	Year Ended December 31, (In thousands, except share and per share data) 2017 2016 2015 Net (loss) income $ (27,916 ) $ (29,537 ) $ 46 Weighted-average shares: Basic 159,224,986 159,045,644 158,036,162 Effect of dilutive securities: Stock options and restricted stock awards — — 4,627,732 Diluted 159,224,986 159,045,644 162,663,894 Net (loss) income per share: Basic $ (0.18 ) $ (0.19 ) $ 0.00 Diluted $ (0.18 ) $ (0.19 ) $ 0.00

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of cash equivalents, restricted cash and marketable securities by security type	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2017 were as follows: Gross Gross Amortized Unrealized Unrealized Estimated (In thousands) Cost Gains Losses Fair Value Included in cash and cash equivalents: Money market funds $ 11,030 $ — $ — $ 11,030 Commercial paper 2,242 — — 2,242 Corporate notes 1,750 — (1 ) 1,749 $ 15,022 $ — $ (1 ) $ 15,021 Restricted cash: Certificate of deposit $ 268 $ — $ — $ 268 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 12,500 $ — $ (40 ) $ 12,460 Commercial paper (due in less than one year) 10,928 4 (1 ) 10,931 Corporate notes (due in less than one year) 55,067 — (107 ) 54,960 Corporate notes (due in one to two years) 14,303 — (62 ) 14,241 $ 92,798 $ 4 $ (210 ) $ 92,592 Cash equivalents, restricted cash and marketable securities by security type at December 31, 2016 were as follows: Gross Gross Amortized Unrealized Unrealized Estimated (In thousands) Cost Gains Losses Fair Value Included in cash and cash equivalents: Money market funds $ 11,193 $ — $ — $ 11,193 Restricted cash: Certificate of deposit $ 268 $ — $ — $ 268 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 5,000 $ — $ (3 ) $ 4,997 Government-sponsored enterprise securities (due in one to two years) 12,500 — (42 ) 12,458 Commercial paper (due in less than one year) 31,024 50 (5 ) 31,069 Corporate notes (due in less than one year) 66,012 4 (47 ) 65,969 Corporate notes (due in one to two years) 1,506 — (10 ) 1,496 $ 116,042 $ 54 $ (107 ) $ 115,989
Schedule of cash equivalents and marketable securities with unrealized losses	2. FAIR VALUE MEASUREMENTS (Continued) Cash equivalents and marketable securities with unrealized losses at December 31, 2017 and 2016 were as follows: Less Than 12 Months 12 Months or Greater Total Gross Gross Gross Estimated Unrealized Estimated Unrealized Estimated Unrealized (In thousands) Fair Value Losses Fair Value Losses Fair Value Losses As of December 31, 2017: Government-sponsored enterprise securities (due in less than one year) $ — $ — $ 12,460 $ (40 ) $ 12,460 $ (40 ) Commercial paper (due in less than one year) 7,717 (1 ) — — 7,717 (1 ) Corporate notes (due in less than one year) 55,210 (106 ) 1,499 (2 ) 56,709 (108 ) Corporate notes (due in one to two years) 14,241 (62 ) — — 14,241 (62 ) $ 77,168 $ (169 ) $ 13,959 $ (42 ) $ 91,127 $ (211 ) As of December 31, 2016: Government-sponsored enterprise securities (due in less than one year) $ 4,997 $ (3 ) $ — $ — $ 4,997 $ (3 ) Government-sponsored enterprise securities (due in one to two years) 12,458 (42 ) — — 12,458 (42 ) Commercial paper (due in less than one year) 8,365 (5 ) — — 8,365 (5 ) Corporate notes (due in less than one year) 39,218 (37 ) 6,944 (10 ) 46,162 (47 ) Corporate notes (due in one to two years) 1,496 (10 ) — — 1,496 (10 ) $ 66,534 $ (97 ) $ 6,944 $ (10 ) $ 73,478 $ (107 )
Schedule of financial instruments measured at fair value on recurring basis	The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2017 and 2016 and indicates the fair value category assigned. Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs (In thousands) Level 1 Level 2 Level 3 Total As of December 31, 2017: Money market funds ( 1) $ 11,030 $ — $ — $ 11,030 Government-sponsored enterprise securities ( 2) — 12,460 — 12,460 Commercial paper ( 1)(2) — 13,173 — 13,173 Corporate notes ( 1)(2)(3) — 70,950 — 70,950 Total $ 11,030 $ 96,583 $ — $ 107,613 As of December 31, 2016: Money market funds ( 1) $ 11,193 $ — $ — $ 11,193 Government-sponsored enterprise securities ( 2)(3) — 17,455 — 17,455 Commercial paper ( 2) — 31,069 — 31,069 Corporate notes ( 2)(3) — 67,465 — 67,465 Total $ 11,193 $ 115,989 $ — $ 127,182 (1) Included in cash and cash equivalents on our balance sheets. (2) Included in current portion of marketable securities on our balance sheets. (3) Included in noncurrent portion of marketable securities on our balance sheets.

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of property and equipment, stated at cost	Property and equipment, stated at cost, is comprised of the following: December 31, (In thousands) 2017 2016 Furniture and computer equipment $ 711 $ 1,268 Lab equipment — 12 Leasehold improvements 111 111 822 1,391 Less accumulated depreciation and amortization (720 ) (1,208 ) $ 102 $ 183

ACCRUED LIABILITIES (Tables)

ACCRUED LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Schedule of accrued liabilities	December 31, (In thousands) 2017 2016 Professional legal and accounting fees $ 272 $ 350 Clinical trial costs 516 723 Other 138 361 $ 926 $ 1,434

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders Equity Note [Abstract]
Schedule of aggregate option and award activity	Aggregate option and award activity for the 2002 Plan, 2011 Plan and 2006 Directors Plan is as follows: Outstanding Options Weighted Average Aggregate Shares Weighted Average Remaining Intrinsic Available Number of Exercise Price Contractual Life Value For Grant Shares Per Share (In years) (In thousands) Balance at December 31, 2016 9,570,535 19,125,287 $ 3.15 Options granted (3,484,000 ) 3,484,000 $ 2.19 Awards granted (72,066 ) — $ — Options exercised — (12,500 ) $ 1.41 Options cancelled/forfeited 188,258 (188,258 ) $ 7.99 Balance at December 31, 2017 6,202,727 22,408,529 $ 2.96 6.24 $ 2,034 Options exercisable at December 31, 2017 17,249,032 $ 3.03 5.57 $ 2,034 Options fully vested and expected to vest at December 31, 2017 22,171,142 $ 2.96 6.21 $ 2,034
Schedule of information about stock options outstanding by exercise price range	8. STOCKHOLDERS’ EQUITY (Continued) Information about stock options outstanding as of December 31, 2017 is as follows: Options Outstanding Weighted Average Weighted Average Remaining Number of Exercise Price Contractual Life Exercise Price Range Shares Per Share (In years) $1.10 - $1.51 5,655,662 $ 1.45 4.89 $1.55 - $2.16 5,631,031 $ 2.08 7.04 $2.22 - $4.34 6,000,783 $ 3.37 7.60 $4.42 - $7.31 5,121,053 $ 5.10 5.27 $1.10 - $7.31 22,408,529 $ 2.96 6.24
Schedule of aggregate restricted stock activity	Aggregate restricted stock activity for the 2011 Plan is as follows: Weighted Average Weighted Average Grant Date Remaining Number of Fair Value Contractual Term Shares Per Share (In years) Non-vested restricted stock at December 31, 2016 — $ — — Granted 72,066 $ 2.20 Vested (72,066 ) $ 2.20 Non-vested restricted stock at December 31, 2017 — $ — —
Summary of allocation of stock-based compensation expense related to share-based payment awards	Year Ended December 31, (In thousands) 2017 2016 2015 Research and development $ 988 $ 1,275 $ 2,139 Restructuring charges — — 307 General and administrative 7,156 6,970 5,951 Stock-based compensation expense included in operating expenses $ 8,144 $ 8,245 $ 8,397
Schedule of assumptions used to estimate the fair value of stock options granted	The fair value of stock options granted in 2017, 2016 and 2015 has been estimated at the date of grant using the Black Scholes option‑pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Dividend yield 0% 0% 0% Expected volatility range 0.884 to 0.892 0.888 to 0.890 0.874 to 0.884 Risk-free interest rate range 1.98% to 1.99% 1.21% to 1.38% 1.68% to 1.71% Expected term 5.5 yrs 5.5 yrs 5.5 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan	8. STOCKHOLDERS’ EQUITY (Continued) The fair value of employee stock purchases in 2017, 2016 and 2015 has been estimated using the Black Scholes option‑pricing model with the following assumptions: Year Ended December 31, 2017 2016 2015 Dividend yield 0% 0% 0% Expected volatility range 0.577 to 0.641 0.641 to 0.684 0.654 to 1.392 Risk-free interest rate range 0.45% to 0.89% 0.28% to 0.45% 0.11% to 0.28% Expected term range 6 - 12 mos 6 - 12 mos 6 - 12 mos
Schedule of common stock reserved for future issuance	Common stock reserved for future issuance as of December 31, 2017 is as follows: Outstanding stock options 22,408,529 Options and awards available for grant 6,202,727 Employee stock purchase plan 895,308 Warrant outstanding 537,893 Total 30,044,457

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of significant components of the entity's deferred tax assets	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred tax assets are as follows: December 31, 2017 2016 (In thousands) Net operating loss carryforwards $ 187,700 $ 280,400 Research credits 34,300 29,800 Capitalized research and development 2,500 300 License fees 100 200 Other-net 8,200 11,500 Total deferred tax assets 232,800 322,200 Valuation allowance for deferred tax assets (232,800 ) (322,200 ) Net deferred tax assets $ — $ —
Schedule of reconciliation of the beginning and ending amounts of unrecognized tax benefits	A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands): Balance as of December 31, 2016 $ 14,700 Increase related to current year tax positions 1,200 Balance as of December 31, 2017 $ 15,900

STATEMENTS OF CASH FLOWS DATA (

STATEMENTS OF CASH FLOWS DATA (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Supplemental schedule of non-cash operating and investing activities	Year Ended December 31, 2017 2016 2015 (In thousands) Supplemental investing activities: Net unrealized (loss) gain on marketable securities $ (154 ) $ 160 $ (129 )

SELECTED QUARTERLY FINANCIAL 29

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of selected quarterly financial information (unaudited)	First Second Third Fourth Quarter Quarter Quarter Quarter (In thousands, except per share amounts) Year Ended December 31, 2017: Revenues $ 537 $ 174 $ 163 $ 191 Operating expenses 8,031 6,905 7,407 7,977 Net loss (7,183 ) (6,405 ) (6,899 ) (7,429 ) Basic and diluted net loss per share $ (0.05 ) $ (0.04 ) $ (0.04 ) $ (0.05 ) Year Ended December 31, 2016: Revenues ( 1) $ 749 $ 211 $ 5,108 $ 94 Operating expenses 9,826 9,122 8,985 8,875 Net loss (8,842 ) (8,637 ) (3,576 ) (8,482 ) Basic and diluted net loss per share $ (0.06 ) $ (0.05 ) $ (0.02 ) $ (0.05 ) (1) The third quarter of 2016 includes the full recognition of the $5,000,000 upfront payment from Janssen Pharmaceuticals as license fee revenue. See Note 4 on License Agreements.

ORGANIZATION AND SUMMARY OF S30

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - NET INCOME (LOSS) PER SHARE (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
Earnings Per Share [Abstract]
Net (loss) income	$ (7,429)	$ (6,899)	$ (6,405)	$ (7,183)	$ (8,482)	$ (3,576)	$ (8,637)	$ (8,842)	$ (27,916)	$ (29,537)	$ 46
Weighted-average shares:
Basic									159,224,986	159,045,644	158,036,162
Effect of dilutive securities from stock options and restricted stock awards											4,627,732
Diluted									159,224,986	159,045,644	162,663,894
Net (loss) income per share:
Basic									$ (0.18)	$ (0.19)	$ 0
Diluted									$ (0.18)	$ (0.19)	$ 0

ORGANIZATION AND SUMMARY OF S31

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ANTI-DILUTIVE SHARES (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share
Potential dilutive securities excluded from diluted earnings (loss) per share calculation (in shares)	14,475,616	11,352,766	9,375,851
Stock options, restricted stock awards excluded from diluted net loss per share calculation due to net loss position
Antidilutive Securities Excluded from Computation of Earnings Per Share
Potential dilutive securities excluded from diluted earnings (loss) per share calculation (in shares)	2,389,310	3,023,520

ORGANIZATION AND SUMMARY OF S32

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - USEFUL LIVES OF ASSETS (Details)	12 Months Ended
	Dec. 31, 2017
Depreciation
Estimated useful lives of assets	4 years

ORGANIZATION AND SUMMARY OF S33

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CONCENTRATIONS OF CUSTOMERS AND SUPPLIERS (Details) - customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration risk
Number of customers	2
Customer | Revenue
Concentration risk
Concentration risk percentage	39.00%	81.00%	96.00%

FAIR VALUE MEASUREMENTS - SECUR

FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Included in cash and cash equivalents:
Amortized Cost	$ 15,022
Gross Unrealized Losses	(1)
Estimated Fair Value	15,021
Restricted cash:
Amortized Cost	268	$ 268
Marketable securities:
Amortized Cost	92,798	116,042
Gross Unrealized Gains	4	54
Gross Unrealized Losses	(210)	(107)
Estimated Fair Value	92,592	115,989
Money market funds
Included in cash and cash equivalents:
Amortized Cost	11,030	11,193
Estimated Fair Value	11,030	11,193
Commercial paper
Included in cash and cash equivalents:
Amortized Cost	2,242
Estimated Fair Value	2,242
Corporate notes
Included in cash and cash equivalents:
Amortized Cost	1,750
Gross Unrealized Losses	(1)
Estimated Fair Value	1,749
Certificate of deposit
Restricted cash:
Amortized Cost	268	268
Estimated Fair Value	268	268
Government-sponsored enterprise securities (due in less than one year)
Marketable securities:
Amortized Cost	12,500	5,000
Gross Unrealized Losses	(40)	(3)
Estimated Fair Value	12,460	4,997
Government-sponsored enterprise securities (due in one to two years)
Marketable securities:
Amortized Cost		12,500
Gross Unrealized Losses		(42)
Estimated Fair Value		12,458
Commercial paper (due in less than one year)
Marketable securities:
Amortized Cost	10,928	31,024
Gross Unrealized Gains	4	50
Gross Unrealized Losses	(1)	(5)
Estimated Fair Value	10,931	31,069
Corporate notes (due in less than one year)
Marketable securities:
Amortized Cost	55,067	66,012
Gross Unrealized Gains		4
Gross Unrealized Losses	(107)	(47)
Estimated Fair Value	54,960	65,969
Corporate notes (due in one to two years)
Marketable securities:
Amortized Cost	14,303	1,506
Gross Unrealized Losses	(62)	(10)
Estimated Fair Value	$ 14,241	$ 1,496

FAIR VALUE MEASUREMENTS - SEC35

FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 77,168	$ 66,534
Less Than 12 Months - Gross Unrealized Losses	(169)	(97)
12 Months or Greater - Estimated Fair Value	13,959	6,944
12 Months or Greater - Gross Unrealized Losses	(42)	(10)
Total - Estimated Fair Value	91,127	73,478
Total - Gross Unrealized Losses	(211)	(107)
Government-sponsored enterprise securities (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value		4,997
Less Than 12 Months - Gross Unrealized Losses		(3)
12 Months or Greater - Estimated Fair Value	12,460
12 Months or Greater - Gross Unrealized Losses	(40)
Total - Estimated Fair Value	12,460	4,997
Total - Gross Unrealized Losses	(40)	(3)
Government-sponsored enterprise securities (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value		12,458
Less Than 12 Months - Gross Unrealized Losses		(42)
Total - Estimated Fair Value		12,458
Total - Gross Unrealized Losses		(42)
Corporate notes (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	55,210	39,218
Less Than 12 Months - Gross Unrealized Losses	(106)	(37)
12 Months or Greater - Estimated Fair Value	1,499	6,944
12 Months or Greater - Gross Unrealized Losses	(2)	(10)
Total - Estimated Fair Value	56,709	46,162
Total - Gross Unrealized Losses	(108)	(47)
Commercial paper (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	7,717	8,365
Less Than 12 Months - Gross Unrealized Losses	(1)	(5)
Total - Estimated Fair Value	7,717	8,365
Total - Gross Unrealized Losses	(1)	(5)
Corporate notes (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	14,241	1,496
Less Than 12 Months - Gross Unrealized Losses	(62)	(10)
Total - Estimated Fair Value	14,241	1,496
Total - Gross Unrealized Losses	$ (62)	$ (10)

FAIR VALUE MEASUREMENTS - RECUR

FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - Recurring basis - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value on a Recurring Basis
Total	$ 107,613	$ 127,182
Money market funds
Fair Value on a Recurring Basis
Total	11,030	11,193
Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	12,460	17,455
Commercial paper
Fair Value on a Recurring Basis
Total	13,173	31,069
Corporate notes
Fair Value on a Recurring Basis
Total	70,950	67,465
Level 1
Fair Value on a Recurring Basis
Total	11,030	11,193
Level 1 | Money market funds
Fair Value on a Recurring Basis
Total	11,030	11,193
Level 2
Fair Value on a Recurring Basis
Total	96,583	115,989
Level 2 | Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	12,460	17,455
Level 2 | Commercial paper
Fair Value on a Recurring Basis
Total	13,173	31,069
Level 2 | Corporate notes
Fair Value on a Recurring Basis
Total	$ 70,950	$ 67,465

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Sienna - Cost-method Investment - USD ($) $ in Thousands	Aug. 03, 2017	Dec. 31, 2017
Schedule Of Cost Method Investments [Line Items]
Number of shares owned		13,842,625
Cost method investment, original cost		$ 0
Trading restriction period	24 months

FAIR VALUE MEASUREMENTS - CREDI

FAIR VALUE MEASUREMENTS - CREDIT RISK (Details)	Dec. 31, 2017Institution
Credit Risk
Number of financial institutions	4

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 822	$ 1,391
Less accumulated depreciation and amortization	(720)	(1,208)
Property and equipment, net	102	183
Furniture and computer equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	711	1,268
Lab equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross		12
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 111	$ 111

LICENSE AGREEMENTS (Details)

LICENSE AGREEMENTS (Details)	Sep. 15, 2016USD ($)item	Dec. 15, 2014USD ($)item	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accrued collaboration charges					$ 1,702,000	$ 3,367,000
Collaboration revenue							$ 35,000,000
License fees and royalties					1,065,000	$ 6,162,000	$ 1,371,000
Janssen Biotech | License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received		$ 35,000,000
Number of agreed upon studies | item		2
Percentage of costs to be paid by Geron		50.00%
Percentage of costs to be paid by Janssen		50.00%
Accrued collaboration charges					$ 1,702,000
Notification period		24 months
Maximum period Geron is obligated to procure supply for manufacturing imetelstat under collaboration agreement		9 months
Collaboration revenue				$ 35,000,000
Janssen Biotech | License agreements | U.S. Opt-In Rights exercised
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron		20.00%
Percentage of costs to be paid by Janssen		80.00%
Continuation Election milestone payment		$ 65,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement		470,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement		$ 350,000,000
Tiered royalties percentage, low end of the range		midteens
Tiered royalties percentage, high end of the range		low twenties
U.S. selling effort percentage		20.00%
Janssen Biotech | License agreements | U.S. Opt-In Rights not exercised
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Continuation Election milestone payment		$ 65,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement		415,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement		350,000,000
Full U.S. Rights fee		$ 70,000,000
Tiered royalties percentage, low end of the range		doubledigit
Tiered royalties percentage, high end of the range		midteens
Janssen Biotech | License Arrangement IP Exclusively Licensed
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron		50.00%
Percentage of costs to be paid by Janssen		50.00%
Janssen Pharmaceuticals Inc | License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Least number of products under License Agreement | item	1
Upfront payment received under license agreement	$ 5,000,000
Aggregate maximum total payments for development and regulatory milestones under license agreement	$ 75,000,000
Tiered royalties percentage range	low single digit
License fees and royalties			$ 5,000,000
Janssen Pharmaceuticals Inc | License Arrangement IP Exclusively Licensed
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron	50.00%
Percentage of costs to be paid by Janssen Pharmaceuticals	50.00%

ACCRUED LIABILITIES (Details)

ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Professional legal and accounting fees	$ 272	$ 350
Clinical trial costs	516	723
Other	138	361
Accrued liabilities	$ 926	$ 1,434

RESTRUCTURING - (Details)

RESTRUCTURING - (Details) - USD ($)	12 Months Ended	22 Months Ended
	Dec. 31, 2015	Dec. 31, 2016
Restructuring
Restructuring charges	$ 1,306,000
Cash payments after adjustments and non-cash credits		$ 988,000
One-time termination benefits
Restructuring
Restructuring charges	1,306,000
Non-cash stock-based compensation expense	$ 307,000

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - Securities Lawsuits	1 Months Ended
	Apr. 30, 2017USD ($)	Dec. 31, 2017lawsuitcase
COMMITMENTS AND CONTINGENCIES
Number of purported class action lawsuits that have been filed | lawsuit		2
Number of cases that have been filed | case		3
Settlement amount paid by entity to settlement escrow account	$ 250,000
Settlement amount paid by insurance providers to settlement escrow account	$ 6,000,000

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Operating Leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Amended operating lease obligation, aggregate future minimum payments	$ 1,435,000
Amended operating lease obligation, aggregate future minimum payments due in 2018	678,000
Amended operating lease obligation, aggregate future minimum payments due in 2019	699,000
Amended operating lease obligation, aggregate future minimum payments due in 2020	58,000
Rent expense under operating leases	$ 691,000	$ 708,000	$ 878,000

COMMITMENTS AND CONTINGENCIES45

COMMITMENTS AND CONTINGENCIES - Severance Plan (Details)	12 Months Ended
	Dec. 31, 2017
Severance Plan
Period within which employee is terminated by entity without cause following a change of control	12 months
Period within which no comparable employment is offered by the entity following a change of control	30 days
Period within which employee resigns following a change of control due to material change in terms of employment	12 months
Minimum
Severance Plan
Period of base salary to be considered for severance payments	2 months
Maximum
Severance Plan
Period of base salary to be considered for severance payments	18 months

STOCKHOLDERS' EQUITY - SALES AG

STOCKHOLDERS' EQUITY - SALES AGREEMENT (Details) - USD ($)	Aug. 28, 2015	Dec. 31, 2017	Dec. 31, 2017
Stockholders Equity Note [Abstract]
Aggregate offering price of common stock	$ 50,000,000
Maximum commission rate (as a percent)	3.00%
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		614,230
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs		$ 1,060,000	$ 1,060,000

STOCKHOLDERS' EQUITY - WARRANTS

STOCKHOLDERS' EQUITY - WARRANTS (Details) - USD ($)	Mar. 31, 2015	Dec. 31, 2017
Warrants Exercised In March 2015
Warrants
Exercise Price (in dollars per share)	$ 3.75
Issuance of common stock upon exercise of warrants (in shares)	235,000
Proceeds from Warrant Exercises	$ 881,000
CIRM | Warrants issued in August 2011
Warrants
Exercise Price (in dollars per share)		$ 3.98
Number of shares into which warrant is converted upon exercise of warrant (in shares)		537,893

STOCKHOLDERS' EQUITY - EQUITY P

STOCKHOLDERS' EQUITY - EQUITY PLANS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 29, 2017
Shares Available For Grant
Balance at the beginning of the period (in shares)	9,570,535
Options granted (in shares)	(3,484,000)
Awards granted (in shares)	(72,066)
Options cancelled/forfeited (in shares)	188,258
Balance at the end of the period (in shares)	6,202,727	9,570,535
Number of Shares - Options Outstanding
Balance at the beginning of the period (in shares)	19,125,287
Options granted (in shares)	3,484,000
Options exercised (in shares)	(12,500)
Options cancelled/forfeited (in shares)	(188,258)
Balance at the end of the period (in shares)	22,408,529	19,125,287
Options exercisable at the end of the period (in shares)	17,249,032	14,074,457	11,356,232
Options fully vested and expected to vest at the end of the period (in shares)	22,171,142
Weighted Average Exercise Price Per Share - Options Outstanding
Balance at the beginning of the period (in dollars per share)	$ 3.15
Options granted (in dollars per share)	2.19
Options exercised (in dollars per share)	1.41
Options cancelled/forfeited (in dollars per share)	7.99
Balance at the end of the period (in dollars per share)	2.96	$ 3.15
Options exercisable at the end of the period (in dollars per share)	3.03	$ 2.99	$ 2.98
Options fully vested and expected to vest at the end of the period (in dollars per share)	$ 2.96
Weight Average Remaining Contractual Life (in years) - Options Outstanding
Balance at the end of the period	6 years 2 months 26 days
Options exercisable at the end of the period	5 years 6 months 25 days
Options fully vested and expected to vest at the end of the period	6 years 2 months 15 days
Aggregate Intrinsic Value - Options Outstanding
Balance at the end of the period (in dollars)	$ 2,034,000
Options exercisable at the end of the period (in dollars)	2,034,000
Options fully vested and expected to vest at the end of the period (in dollars)	2,034,000
Closing stock price (in dollars per share)				$ 1.80
Total pretax intrinsic value of stock options exercised (in dollars)	15,000	$ 595,000	$ 2,398,000
Cash received from exercise of options (in dollars)	$ 18,000	$ 493,000	$ 2,205,000
2002 Plan
STOCKHOLDERS' EQUITY
Vesting period of options	4 years
Exercise price as a percentage of fair market value	100.00%
2002 Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years
2011 Plan
STOCKHOLDERS' EQUITY
Vesting period of options	4 years
Minimum percentage of ownership required for granting options at least 110% of fair market value of common stock	10.00%
Minimum exercise price as a percentage of fair market value for employees having more than 10 % outstanding common stock	110.00%
Maximum expiration term of options granted to employees having more than 10 % outstanding common stock	5 years
Shares Available For Grant
Balance at the end of the period (in shares)	6,202,727
2011 Plan | First Director Option
STOCKHOLDERS' EQUITY
Vesting period of options	3 years
Options to be granted to purchase shares upon appointment (shares)	100,000
2011 Plan | Subsequent Director Option
STOCKHOLDERS' EQUITY
Options to be granted to purchase shares (in shares)	50,000
2011 Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years
2006 Directors Plan | First Director Option
STOCKHOLDERS' EQUITY
Vesting period of options	3 years
2006 Directors Plan | Subsequent Director Option
STOCKHOLDERS' EQUITY
Vesting period of options	1 year
2006 Directors Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years

STOCKHOLDERS' EQUITY - STOCK OP

STOCKHOLDERS' EQUITY - STOCK OPTIONS OUTSTANDING (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
$1.10 - $1.51
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.10
Exercise price, high end of range (in dollars per share)	$ 1.51
Options Outstanding
Number of Shares | shares	5,655,662
Weighted Average Exercise Price Per Share (in dollars per share)	$ 1.45
Weighted Average Remaining Contractual Life (In years)	4 years 10 months 20 days
$1.55 - $2.16
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.55
Exercise price, high end of range (in dollars per share)	$ 2.16
Options Outstanding
Number of Shares | shares	5,631,031
Weighted Average Exercise Price Per Share (in dollars per share)	$ 2.08
Weighted Average Remaining Contractual Life (In years)	7 years 14 days
$2.22 - $4.34
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 2.22
Exercise price, high end of range (in dollars per share)	$ 4.34
Options Outstanding
Number of Shares | shares	6,000,783
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.37
Weighted Average Remaining Contractual Life (In years)	7 years 7 months 6 days
$4.42 - $7.31
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 4.42
Exercise price, high end of range (in dollars per share)	$ 7.31
Options Outstanding
Number of Shares | shares	5,121,053
Weighted Average Exercise Price Per Share (in dollars per share)	$ 5.10
Weighted Average Remaining Contractual Life (In years)	5 years 3 months 7 days
$1.10 - $7.31
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$ 1.10
Exercise price, high end of range (in dollars per share)	$ 7.31
Options Outstanding
Number of Shares | shares	22,408,529
Weighted Average Exercise Price Per Share (in dollars per share)	$ 2.96
Weighted Average Remaining Contractual Life (In years)	6 years 2 months 26 days

STOCKHOLDERS' EQUITY - RESTRICT

STOCKHOLDERS' EQUITY - RESTRICTED STOCK ACTIVITY (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Granted (in shares)	72,066
Restricted stock awards
Number of Shares
Granted (in shares)	72,066
Vested (in shares)	(72,066)
Weighted Average Grant Date Fair Value Per Share
Granted (in dollars per share)	$ 2.20	$ 2.44	$ 3.75
Vested (in dollars per share)	$ 2.20
Other disclosures
Total fair value of restricted stock that vested	$ 159,000	$ 54,000	$ 275,000

STOCKHOLDERS' EQUITY - EMPLOYEE

STOCKHOLDERS' EQUITY - EMPLOYEE STOCK PURCHASE PLAN (Details) - Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2017itemshares
Employee Stock Purchase Plan
Shares of common stock authorized for issuance | shares	1,000,000
Aggregate shares issued under plan | shares	104,692
Maximum duration of offering period	12 months
Number of offering periods in which an employee can participate at a time | item	1
Number of consecutive purchase periods in an offering period | item	2
Duration of the purchase period	6 months
Maximum percentage of annual salary that can be withheld	10.00%
Percentage applied to common stock market value in calculating purchase price under purchase plan	85.00%
Duration of the new offering period	12 months

STOCKHOLDERS' EQUITY - STOCK-BA

STOCKHOLDERS' EQUITY - STOCK-BASED COMPENSATION EXPENSE FOR EMPLOYEES AND DIRECTORS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 8,144	$ 8,245	$ 8,397
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	988	1,275	2,139
Restructuring charges
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses			307
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 7,156	$ 6,970	$ 5,951

STOCKHOLDERS' EQUITY - PRICING

STOCKHOLDERS' EQUITY - PRICING MODEL ASSUMPTIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation cost related to unvested stock awards not yet recognized
Compensation cost not yet recognized, net of estimated forfeitures (in dollars)	$ 8,008,000
Period for recognition of compensation cost on weighted average basis	26 months
Stock Options
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected volatility range, minimum (as a percent)	88.40%	88.80%	87.40%
Expected volatility range, maximum (as a percent)	89.20%	89.00%	88.40%
Risk-free interest rate range, minimum (as a percent)	1.98%	1.21%	1.68%
Risk-free interest rate range, maximum (as a percent)	1.99%	1.38%	1.71%
Expected term	5 years 6 months	5 years 6 months	5 years 6 months
Additional disclosures
Weighted average estimated fair value of employee stock options granted (in dollars per share)	$ 1.58	$ 1.83	$ 3.06
Employee Stock Purchase Plan
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected volatility range, minimum (as a percent)	57.70%	64.10%	65.40%
Expected volatility range, maximum (as a percent)	64.10%	68.40%	139.20%
Risk-free interest rate range, minimum (as a percent)	0.45%	0.28%	0.11%
Risk-free interest rate range, maximum (as a percent)	0.89%	0.45%	0.28%
Additional disclosures
Weighted average estimated fair value of purchase rights (in dollars per share)	$ 0.75	$ 1.01	$ 1.64
Employee Stock Purchase Plan | Minimum
Assumptions used to estimate fair value of awards
Expected term	6 months	6 months	6 months
Employee Stock Purchase Plan | Maximum
Assumptions used to estimate fair value of awards
Expected term	12 months	12 months	12 months

STOCKHOLDERS' EQUITY - 401(k) P

STOCKHOLDERS' EQUITY - 401(k) PLAN (Details)	12 Months Ended
	Dec. 31, 2013
401(k) Plan
Period of vesting of matching contributions	4 years

STOCKHOLDERS' EQUITY - STOCK-55

STOCKHOLDERS' EQUITY - STOCK-BASED COMPENSATION TO SERVICE PROVIDERS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-Based Compensation to Service Providers
Stock-based compensation for services by non-employees	$ 200,000	$ 156,000	$ 364,000
Common Stock
Stock-Based Compensation to Service Providers
Shares issued (in shares)	72,066	21,541	18,077
Consultants | Stock Options
Stock-Based Compensation to Service Providers
Stock-based compensation for services by non-employees	$ 41,000	$ 104,000	$ 311,000
Directors and Consultants | Common Stock
Stock-Based Compensation to Service Providers
Stock-based compensation for services by non-employees	$ 159,000	$ 52,000	$ 53,000
Shares issued (in shares)	72,066	21,541	18,077

STOCKHOLDERS' EQUITY - COMMON S

STOCKHOLDERS' EQUITY - COMMON STOCK RESERVED FOR FUTURE ISSUANCE (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
STOCKHOLDERS' EQUITY
Outstanding stock options (in shares)	22,408,529	19,125,287
Options and awards available for grant (in shares)	6,202,727	9,570,535
Warrant outstanding (in shares)	537,893
Common stock reserved for future issuance (in shares)	30,044,457
Employee Stock
STOCKHOLDERS' EQUITY
Common stock reserved for future issuance (in shares)	895,308

INCOME TAXES - DEFERRED TAXES (

INCOME TAXES - DEFERRED TAXES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant components of deferred tax assets
Net operating loss carryforwards	$ 187,700,000	$ 280,400,000
Research credits	34,300,000	29,800,000
Capitalized research and development	2,500,000	300,000
License fees	100,000	200,000
Other-net	8,200,000	11,500,000
Total deferred tax assets	232,800,000	322,200,000
Valuation allowance for deferred tax assets	(232,800,000)	(322,200,000)
Valuation allowance
Increase (decrease) in valuation allowance	$ (89,400,000)	$ 9,600,000	$ (2,300,000)

INCOME TAXES - OPERATING LOSS C

INCOME TAXES - OPERATING LOSS CARRYFORWARDS (Details)	Dec. 31, 2017USD ($)
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 793,900,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 300,200,000

INCOME TAXES - TAX CREDIT CARRY

INCOME TAXES - TAX CREDIT CARRYFORWARDS (Details) - Research and Development	Dec. 31, 2017USD ($)
Federal
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 34,000,000
State
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 19,100,000

INCOME TAXES - TAX CUT AND JOBS

INCOME TAXES - TAX CUT AND JOBS ACT (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Tax Cuts And Jobs Act [Line Items]
Federal corporate tax rate		35.00%
Impact on deferred tax assets due to corporate tax rate reduction		$ 102,300,000
Scenario, Forecast
Tax Cuts And Jobs Act [Line Items]
Federal corporate tax rate	21.00%

INCOME TAXES - UNRECOGNIZED TAX

INCOME TAXES - UNRECOGNIZED TAX BENEFITS (Details)	12 Months Ended
	Dec. 31, 2017USD ($)
Unrecognized tax benefits
Unrecognized tax benefits, if recognized would impact effective tax rate	$ 15,900,000
Balance at the beginning of the period	14,700,000
Increase related to current year tax positions	1,200,000
Balance at the end of the period	$ 15,900,000

STATEMENTS OF CASH FLOWS DATA62

STATEMENTS OF CASH FLOWS DATA (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental investing activities:
Net unrealized (loss) gain on marketable securities	$ (154)	$ 160	$ (129)

SELECTED QUARTERLY FINANCIAL 63

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($)	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
Revenues	$ 191,000	$ 163,000	$ 174,000	$ 537,000	$ 94,000	$ 5,108,000	$ 211,000	$ 749,000	$ 1,065,000	$ 6,162,000	$ 36,371,000
Operating expenses	7,977,000	7,407,000	6,905,000	8,031,000	8,875,000	8,985,000	9,122,000	9,826,000	30,320,000	36,808,000	36,930,000
Net loss	$ (7,429,000)	$ (6,899,000)	$ (6,405,000)	$ (7,183,000)	$ (8,482,000)	$ (3,576,000)	$ (8,637,000)	$ (8,842,000)	(27,916,000)	(29,537,000)	46,000
Basic and diluted net loss per share	$ (0.05)	$ (0.04)	$ (0.04)	$ (0.05)	$ (0.05)	$ (0.02)	$ (0.05)	$ (0.06)
License fees and royalties									$ 1,065,000	$ 6,162,000	$ 1,371,000
Janssen Pharmaceuticals Inc | License agreements
License fees and royalties						$ 5,000,000

SUBSEQUENT EVENT (Details)

SUBSEQUENT EVENT (Details) - USD ($)	1 Months Ended		12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2017
Subsequent Event [Line Items]
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		614,230
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs		$ 1,060,000	$ 1,060,000
Subsequent Event
Subsequent Event [Line Items]
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)	776,788
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs	$ 1,553,000