Geron (GERN) 10-Q 31 Jul 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 24, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	GERON CORP
Entity Central Index Key	886,744
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		183,622,026
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	GERN

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 19,127	$ 16,335
Restricted cash	269	268
Marketable securities	141,800	78,351
Interest and other receivables	773	436
Prepaid assets	301	580
Total current assets	162,270	95,970
Noncurrent marketable securities	20,250	14,241
Property and equipment, net	71	102
Other assets	676
Total assets	183,267	110,313
Current liabilities:
Accounts payable	458	503
Accrued compensation and benefits	1,531	3,385
Accrued collaboration charges	2,192	1,702
Other accrued liabilities	724	926
Total current liabilities	4,905	6,516
Commitments and contingencies
Stockholders' equity:
Common stock	183	160
Additional paid-in capital	1,176,823	1,089,684
Accumulated deficit	(998,567)	(985,840)
Accumulated other comprehensive loss	(77)	(207)
Total stockholders' equity	178,362	103,797
Total liabilities and stockholders' equity	$ 183,267	$ 110,313

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
License fees and royalties	$ 208	$ 174	$ 526	$ 711
Operating expenses:
Research and development	3,204	2,499	5,644	5,873
General and administrative	4,246	4,406	9,561	9,063
Total operating expenses	7,450	6,905	15,205	14,936
Loss from operations	(7,242)	(6,731)	(14,679)	(14,225)
Interest and other income	717	346	1,111	678
Change in fair value of equity investment	(350)		(475)
Other expense	(59)	(20)	(77)	(41)
Net loss	$ (6,934)	$ (6,405)	$ (14,120)	$ (13,588)
Basic and diluted net loss per share	$ (0.04)	$ (0.04)	$ (0.08)	$ (0.09)
Shares used in computing basic and diluted net loss per share	174,475,244	159,182,367	167,538,530	159,171,959

CONDENSED STATEMENTS OF COMPREH

CONDENSED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,934)	$ (6,405)	$ (14,120)	$ (13,588)
Net unrealized gain (loss) on marketable securities	254	(8)	130	(26)
Comprehensive loss	$ (6,680)	$ (6,413)	$ (13,990)	$ (13,614)

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (14,120)	$ (13,588)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	31	38
Loss on retirement of property and equipment		5
Accretion and amortization on investments, net	(111)	144
Change in fair value of equity investment, including foreign currency translation	513
Stock-based compensation for services by non-employees	120	115
Stock-based compensation for employees and directors	3,159	4,058
Amortization related to 401(k) contributions	10	32
Changes in assets and liabilities:
Current assets	146	(5,954)
Current liabilities	(1,611)	3,405
Net cash used in operating activities	(11,863)	(11,745)
Cash flows from investing activities:
Purchases of marketable securities	(107,067)	(60,436)
Proceeds from maturities of marketable securities	37,850	65,940
Net cash (used in) provided by investing activities	(69,217)	5,504
Cash flows from financing activities:
Proceeds from issuances of common stock, net of issuance costs	83,873	37
Net cash provided by financing activities	83,873	37
Net increase (decrease) in cash, cash equivalents and restricted cash	2,793	(6,204)
Cash, cash equivalents and restricted cash at the beginning of the period	16,603	13,078
Cash, cash equivalents and restricted cash at the end of the period	$ 19,396	$ 6,874

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The terms “Geron”, the “Company”, “we” and “us” as used in this report refer to Geron Corporation. The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting only of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or any other period. These financial statements and notes should be read in conjunction with the financial statements for each of the three years ended December 31, 2017, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2017 has been derived from audited financial statements at that date. Prior Period Reclassification With the adoption of Accounting Standards Update, or ASU, No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash 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 would be 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 consist of outstanding stock options and warrants to purchase our common stock. Diluted net loss per share excludes potential common shares outstanding for all periods presented as their effect would be anti-dilutive. Accordingly, basic and diluted net loss per share is the same for all periods presented in the accompanying condensed statements of operations. Since we incurred a net loss for the three and six months ended June 30, 2018 and 2017, the diluted net loss per share calculation excludes potential common shares of 26,306,263 and 23,044,422, respectively, related to outstanding stock options and warrants as their effect would have been anti-dilutive. 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 and equity investments, 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 and cash operating accounts. We classify our marketable debt 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 condensed statements of operations. We recognize a charge when the declines in the fair values below the amortized cost bases 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 three and six months ended June 30, 2018 and 2017. See Note 2 on Fair Value Measurements. Equity Investments With the adoption of ASU No. 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities Revenue Recognition Beginning January 1, 2018, we recognize revenue in accordance with the provisions of Accounting Standards Codification Topic 606, Revenue from Contracts with Customers A performance obligation is a promise in an agreement to transfer a distinct good or service to the customer and is the unit of account in Topic 606. Significant management judgment is required to determine the level of effort required and the period over which completion of the performance obligations is expected under an agreement. If reasonable estimates regarding when performance obligations are either complete or substantially complete cannot be made, then revenue recognition is deferred until a reasonable estimate can be made. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. We allocate the total transaction price to each performance obligation based on the estimated relative stand-alone selling prices of the promised goods or services underlying each performance obligation. Estimated selling prices for license rights are calculated using an income approach model and include the following key assumptions, judgments and estimates: the development timeline, revenue forecast, commercialization expenses, discount rate and probabilities of technical and regulatory success. Following is a description of the principal activities from which we generate revenue. Collaboration revenue primarily represents amounts earned under the collaboration and license agreement, or Collaboration Agreement, with Janssen Biotech, Inc., or Janssen, for the imetelstat program. License fees and royalty revenue primarily represents amounts earned under agreements that out-license our technology to various companies. License and/or Collaboration Agreements In addition to the Collaboration Agreement (which is more fully described in Note 3 on Collaboration Agreement), we have entered into several license 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, annual license maintenance fees, cost sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. Non-refundable upfront fees, annual license maintenance fees and funding of research and development activities are considered fixed, while milestone payments and royalties are identified as variable consideration. Licenses of Intellectual Property. If we determine the license to intellectual property is distinct from the other performance obligations identified in the agreement and the licensee can use and benefit from the license, we recognize revenue from non-refundable upfront fees allocated to the license upon the completion of the transfer of the license to the licensee. For such licenses, we recognize revenue from annual license maintenance fees upon the start of the new license period. For licenses that are bundled with other performance obligations, we assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable upfront fees or annual license maintenance fees. At each reporting period, we reassess the progress and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments . At the inception of each agreement that includes milestone payments, we evaluate whether the milestones are considered probable of being achieved and estimate the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone is included in the transaction price. For milestones that we do not deem to be probable of being achieved, the associated milestone payments are fully constrained and the value of the milestone is excluded from the transaction price with no revenue being recognized. Milestone payments that are not within our control, such as regulatory-related accomplishments, are not considered probable of being achieved until those accomplishments have been communicated by the relevant regulatory authority. Once the assessment of probability of achievement becomes probable, we recognize revenue for the milestone payment under collaboration revenue. At each reporting period, we assess the probability of achievement of each milestone under our current agreements. Royalties . For agreements with sales-based royalties, including milestone payments based on the level of sales, where the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (a) when the related sales occur, or (b) when the performance obligation, to which some or all of the royalty has been allocated, has been satisfied (or partially satisfied). At each reporting period, we estimate the sales incurred by each licensee based on historical experience and accrue the associated royalty amount. Cost Sharing Arrangements . Research and development and other expenses being shared by both parties under an agreement are recorded as earned or owed based on the performance obligations by both parties under the respective agreement. 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 over time in a manner proportionate to the costs we incurred to perform the services using the input method. 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. 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 of clinical trial costs 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 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 included in operating expenses on our condensed statements of operations related to stock options and employee stock purchases for the three and six months ended June 30, 2018 and 2017 which was allocated as follows: Three Months Ended June 30, Six Months Ended June 30, (In thousands) 2018 2017 2018 2017 Research and development $ 266 $ 250 $ 421 $ 541 General and administrative 1,279 1,825 2,738 3,517 Stock-based compensation expense included in operating expenses $ 1,545 $ 2,075 $ 3,159 $ 4,058 As stock-based compensation expense recognized in our condensed statements of operations for the three and six months ended June 30, 2018 and 2017 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. Stock Options We grant options with service-based vesting under our equity plans to employees, non-employee directors and consultants. The vesting period for employee options is generally four years. The fair value of options granted during the six months ended June 30, 2018 and 2017 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.821 to 0.832 0.884 to 0.892 Risk-free interest rate range 2.55% to 2.94% 1.98% to 1.99% Expected term 5.25 yrs 5.5 yrs Employee Stock Purchase Plan The fair value of employees’ purchase rights during the six months ended June 30, 2018 and 2017 has been estimated using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.437 to 0.475 0.577 to 0.641 Risk-free interest rate range 1.53% to 1.76% 0.45% to 0.89% Expected term range 6 - 12 mos 6 - 12 mos Dividend yield is based on historical cash dividend payments. The expected volatility is based on historical volatilities of our stock since traded options on Geron stock do not correspond to option terms and the trading volume of options is limited. The risk-free interest rate 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. Non-Employee Stock-Based Awards 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 condensed statements of operations. 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 New Accounting Pronouncements – Recently Adopted In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09, which amends the guidance for accounting for revenue from contracts with customers. This ASU superseded the revenue recognition requirements in Accounting Standards Codification Topic 605, Revenue Recognition We adopted Topic 606 on January 1, 2018 using the modified retrospective transition method for those agreements which were not completed as of January 1, 2018. Financial results for the reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts have not been adjusted and continue to be reported in accordance with our historical accounting under Topic 605. In connection with the adoption of Topic 606, we recognized a cumulative-effect adjustment to our opening balance of accumulated deficit and an increase to interest and other receivables of $204,000 as of January 1, 2018 for projected sales-based royalties on product sales occurring in 2017 for which payments had not yet been received as of December 31, 2017. Such royalties were recognized as revenue in prior periods when payments were received from our licensees. In accordance with Topic 606-10-50-14a, we have elected to exclude providing further information about our sales-based royalties. The adoption of Topic 606 did not result in any changes to the estimated transaction price or the performance obligations for current agreements or the amounts allocated to satisfied performance obligations. We do not have any deferred revenue associated with unsatisfied performance obligations. Since we view our operations as a single segment and all of our revenues are recognized at a point in time from similar license agreements, disaggregated revenue disclosures would not materially provide additional information. We do not expect the application of Topic 606 to have a material impact on our financial results on an ongoing basis in comparison to results that would have been realized if we had continued to apply Topic 605. In January 2016, the FASB issued ASU 2016-01 which requires equity investments to be measured at fair value with changes in fair value recognized in the statements of operations. To further clarify ASU 2016-01, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities in Sienna Cancer Diagnostics Limited, or Sienna we remeasured the fair value of our equity investment in Sienna at each reporting date in 2018 The cumulative-effect adjustments to our January 1, 2018 condensed balance sheet for the adoption of Topic 606 and ASU 2016-01 and ASU 2018-03 were as follows (in thousands): Condensed Balance Sheet Balance at December 31, 2017 Adjustments Due to Topic 606 Adjustments Due to ASU 2016-01 and ASU 2018-03 Balance at January 1, 2018 Assets: Interest and other receivables $ 436 $ 204 $ - $ 640 Other assets $ - $ - $ 1,189 $ 1,189 Stockholders’ Equity: Accumulated deficit $ (985,840 ) $ 204 $ 1,189 $ (984,447 ) As of January 1, 2018, we also adopted ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments Statement of Cash Flows (Topic 230) Restricted Cash Compensation — Stock Compensation: Scope of Modification Accounting New Accounting Pronouncements – Issued But Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2018
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 June 30, 2018 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 $ 11,450 $ - $ - $ 11,450 Commercial paper 5,689 1 (1 ) 5,689 $ 17,139 $ 1 $ (1 ) $ 17,139 Restricted cash: Certificate of deposit $ 269 $ - $ - $ 269 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 10,000 $ - $ (10 ) $ 9,990 Commercial paper (due in less than one year) 56,917 181 (4 ) 57,094 Corporate notes (due in less than one year) 74,930 - (214 ) 74,716 Corporate notes (due in one to two years) 20,280 - (30 ) 20,250 $ 162,127 $ 181 $ (258 ) $ 162,050 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 and marketable securities with unrealized losses that have been in a continuous unrealized loss position for less than 12 months and 12 months or longer at June 30, 2018 and December 31, 2017 were as follows: Less Than 12 Months 12 Months or Longer Total Gross Gross Gross Estimated Unrealized Estimated Unrealized Estimated Unrealized (In thousands) Fair Value Losses Fair Value Losses Fair Value Losses As of June 30, 2018: Government-sponsored enterprise securities (due in less than one year) $ - $ - $ 9,990 $ (10 ) $ 9,990 $ (10 ) Commercial paper (due in less than one year) 10,639 (5 ) - - 10,639 (5 ) Corporate notes (due in less than one year) 62,975 (184 ) 10,241 (30 ) 73,216 (214 ) Corporate notes (due in one to two years) 20,250 (30 ) - - 20,250 (30 ) $ 93,864 $ (219 ) $ 20,231 $ (40 ) $ 114,095 $ (259 ) 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 ) The gross unrealized losses related to government-sponsored enterprise securities, commercial paper and corporate notes as of June 30, 2018 and December 31, 2017 were due to changes in interest rates and not credit risk. We determined that the gross unrealized losses on our marketable securities as of June 30, 2018 and December 31, 2017 were temporary in nature. We review our investments quarterly to identify and evaluate whether any investments have indications of possible other-than-temporary 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 amortized 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 condensed 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 an 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. 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 condensed 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, corporate notes and equity investments 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 June 30, 2018 and December 31, 2017 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 June 30, 2018: Money market funds (1) $ 11,450 $ - $ - $ 11,450 Government-sponsored enterprise securities (2) - 9,990 - 9,990 Commercial paper (1)(2) - 62,783 - 62,783 Corporate notes (2)(3) - 94,966 - 94,966 Equity investment (4) - 676 - 676 Total $ 11,450 $ 168,415 $ - $ 179,865 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 (1) Included in cash and cash equivalents on our condensed balance sheets. (2) Included in current portion of marketable securities on our condensed balance sheets. (3) Included in noncurrent portion of marketable securities on our condensed balance sheets. (4) Included in other assets on our condensed balance sheets. See “Equity Investment” in this Note 2 on Fair Value Measurements for further discussion of this equity investment. Equity Investment In December 2007, we received 13,842,625 ordinary shares in Sienna in connection with a license we granted to them for our human telomerase reverse transcriptase, or hTERT, technology for use in human diagnostics. The shares were recorded at a zero cost basis upon receipt 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. In connection with Sienna’s initial public offering under Australian securities regulations, we signed a restriction agreement with Sienna which subjects our shares in Sienna to a 24-month trading restriction from the effective date of Sienna’s listing on the ASX. Due to this trading restriction, under the cost method of accounting, we maintained a zero cost basis for our shares in Sienna as of December 31, 2017. With the adoption of ASU 2016-01 and ASU 2018-03, as described in Note 1 on Summary of Significant Accounting Policies, our equity investment in Sienna must be reported at fair value and therefore, we recorded a cumulative-effect adjustment of $1,189,000 on our condensed balance sheet for the fair value of our shares in Sienna, as measured using the closing stock price reported on the ASX and converted to U.S. dollars as of January 1, 2018. As of June 30, 2018, the fair value of our shares in Sienna was $676,000. In accordance with ASU 2016-01, we remeasured the fair value of our shares in Sienna at each reporting date in 2018 and recognized the resulting change in fair value of $388,000 and $513,000, respectively, for the three and six months ended June 30, 2018, both of which include a loss of $38,000 related to foreign currency translation.

COLLABORATION AGREEMENT

COLLABORATION AGREEMENT	6 Months Ended
	Jun. 30, 2018
Collaborative Arrangement Disclosure [Abstract]
COLLABORATION AGREEMENT	3. COLLABORATION 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 in December 2014, we received $35,000,000 from Janssen as an upfront payment. 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 June 30, 2018, accrued collaboration charges of $2,192,000 on our condensed 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 June 30, 2018. 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. The protocol-specified primary analysis of IMbark, which includes an assessment of overall survival, was initiated by Janssen in the second quarter of 2018 with a clinical cut-off date of April 26, 2018. We expect Janssen to inform us of its decision by the end of the third quarter of 2018. 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 and 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. After an affirmative Continuation Decision by Janssen, if any, 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. 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, if any, (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 or regulatory milestones, represent fully constrained variable consideration under Topic 606 as achievement of these milestones has not been deemed probable as of June 30, 2018. Royalties on future product sales of imetelstat, if successfully commercialized under the Collaboration Agreement, and any sales-based milestone payments will be recognized as revenue at the later of (a) when the related sales occur, or (b) when the performance obligation, to which some or all of the royalty has been allocated, has been satisfied (or partially satisfied) in accordance with Topic 606.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	6 Months Ended
	Jun. 30, 2018
Stockholders Equity Note [Abstract]
STOCKHOLDERS' EQUITY	4. STOCKHOLDERS’ EQUITY At Market Issuance Sales Agreements On August 28, 2015, we entered into an At Market Issuance Sales Agreement, or the 2015 Sales Agreement, with MLV & Co. LLC, or MLV, under which we could elect to issue and sell shares of our common stock having an aggregate offering price of up to $50,000,000. Pursuant to the 2015 Sales Agreement, common stock was sold at market prices prevailing at the time of sale through MLV as our sales agent. We paid 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. During the six months ended June 30, 2018, we completed the sale of the remaining common stock subject to the 2015 Sales Agreement and issued an aggregate of 13,195,106 shares of our common stock, resulting in net cash proceeds to us of approximately $47,651,000 after deducting sales commissions and offering expenses payable by us. No further shares of common stock may be sold under the 2015 Sales Agreement. On May 18, 2018, we entered into an At Market Issuance Sales Agreement, or the 2018 Sales Agreement, with B. Riley FBR, Inc., or B. Riley FBR, pursuant to which we may elect to issue and sell shares of our common stock having an aggregate offering price of up to $100,000,000 in such quantities and on such minimum price terms as we set from time to time through B. Riley FBR as our sales agent. We pay B. Riley FBR 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 B. Riley FBR under the 2018 Sales Agreement. During the three months ended June 30, 2018, we sold an aggregate of 9,447,026 shares of our common stock pursuant to the 2018 Sales Agreement, resulting in net cash proceeds to us of approximately $36,208,000 after deducting sales commissions and offering expenses payable by us. The 2018 Sales Agreement will expire upon the earlier of: (a) the sale of all common stock subject to the 2018 Sales Agreement and (b) May 18, 2021. 2018 Equity Incentive Plan On May 15, 2018, our stockholders approved the adoption of the 2018 Equity Incentive Plan, or 2018 Plan, as the successor to our 2011 Incentive Award Plan, or 2011 Plan. The 2018 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, other stock awards, and performance awards that may be settled in cash, stock, or other property. Eligible participants under the 2018 Plan include our employees, consultants and directors. The number of shares reserved for issuance under the 2018 Plan (subject to adjustment for certain changes in capitalization) is equal to the sum of (i) the unallocated shares of common stock remaining available for grant under the 2011 Plan as of May 15, 2018, (ii) 10,000,000 newly reserved shares of common stock and (iii) the number of shares subject to awards granted under the Amended and Restated 2002 Equity Incentive Plan, or 2002 Plan, and the 2011 Plan as such shares become available from time to time, referred to as the Prior Plans’ Returning Shares. Such Prior Plans’ Returning Shares become available for issuance under the 2018 Plan if outstanding stock awards granted under the 2002 Plan and the 2011 Plan, after May 15, 2018, expire or terminate for any reason prior to exercise or settlement or are forfeited, cancelled or otherwise returned to us because of the failure to meet a contingency or condition required for the vesting of such shares, or, subject to certain exceptions, are reacquired or withheld (or not issued) by us to satisfy a tax withholding obligation in connection with a stock award. As a result of the approval of the 2018 Plan, no additional awards may be granted from the 2011 Plan.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
	Jun. 30, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	5. SUBSEQUENT EVENTS 2018 Sales Agreement In July 2018, we sold an aggregate of 636,053 shares of our common stock pursuant to the 2018 Sales Agreement, resulting in net cash proceeds to us of approximately $2,167,000 after deducting sales commissions and estimated offering expenses payable by us. For further discussion of the 2018 Sales Agreement, see Note 4 on Stockholders’ Equity. 2011 Incentive Award Plan In July 2018, outstanding stock options to purchase 438,902 shares of our common stock with a weighted average exercise price of $1.71 per share under the 2011 Plan were exercised resulting in cash proceeds to us of approximately $749,000.

SUMMARY OF SIGNIFICANT ACCOUN11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The terms “Geron”, the “Company”, “we” and “us” as used in this report refer to Geron Corporation. The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting only of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or any other period. These financial statements and notes should be read in conjunction with the financial statements for each of the three years ended December 31, 2017, included in the Company’s Annual Report on Form 10-K. The accompanying condensed balance sheet as of December 31, 2017 has been derived from audited financial statements at that date.
Prior Period Reclassification	Prior Period Reclassification With the adoption of Accounting Standards Update, or ASU, No. 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash
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 would be 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 consist of outstanding stock options and warrants to purchase our common stock. Diluted net loss per share excludes potential common shares outstanding for all periods presented as their effect would be anti-dilutive. Accordingly, basic and diluted net loss per share is the same for all periods presented in the accompanying condensed statements of operations. Since we incurred a net loss for the three and six months ended June 30, 2018 and 2017, the diluted net loss per share calculation excludes potential common shares of 26,306,263 and 23,044,422, respectively, related to outstanding stock options and warrants as their effect would have been anti-dilutive.
Use of Estimates	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 and equity investments, 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 and cash operating accounts. We classify our marketable debt 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 condensed statements of operations. We recognize a charge when the declines in the fair values below the amortized cost bases 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 three and six months ended June 30, 2018 and 2017. See Note 2 on Fair Value Measurements. Equity Investments With the adoption of ASU No. 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities
Revenue Recognition	Revenue Recognition Beginning January 1, 2018, we recognize revenue in accordance with the provisions of Accounting Standards Codification Topic 606, Revenue from Contracts with Customers A performance obligation is a promise in an agreement to transfer a distinct good or service to the customer and is the unit of account in Topic 606. Significant management judgment is required to determine the level of effort required and the period over which completion of the performance obligations is expected under an agreement. If reasonable estimates regarding when performance obligations are either complete or substantially complete cannot be made, then revenue recognition is deferred until a reasonable estimate can be made. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. We allocate the total transaction price to each performance obligation based on the estimated relative stand-alone selling prices of the promised goods or services underlying each performance obligation. Estimated selling prices for license rights are calculated using an income approach model and include the following key assumptions, judgments and estimates: the development timeline, revenue forecast, commercialization expenses, discount rate and probabilities of technical and regulatory success. Following is a description of the principal activities from which we generate revenue. Collaboration revenue primarily represents amounts earned under the collaboration and license agreement, or Collaboration Agreement, with Janssen Biotech, Inc., or Janssen, for the imetelstat program. License fees and royalty revenue primarily represents amounts earned under agreements that out-license our technology to various companies. License and/or Collaboration Agreements In addition to the Collaboration Agreement (which is more fully described in Note 3 on Collaboration Agreement), we have entered into several license 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, annual license maintenance fees, cost sharing arrangements, milestone payments, royalties on future sales of products, or any combination of these items. Non-refundable upfront fees, annual license maintenance fees and funding of research and development activities are considered fixed, while milestone payments and royalties are identified as variable consideration. Licenses of Intellectual Property. If we determine the license to intellectual property is distinct from the other performance obligations identified in the agreement and the licensee can use and benefit from the license, we recognize revenue from non-refundable upfront fees allocated to the license upon the completion of the transfer of the license to the licensee. For such licenses, we recognize revenue from annual license maintenance fees upon the start of the new license period. For licenses that are bundled with other performance obligations, we assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable upfront fees or annual license maintenance fees. At each reporting period, we reassess the progress and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments . At the inception of each agreement that includes milestone payments, we evaluate whether the milestones are considered probable of being achieved and estimate the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone is included in the transaction price. For milestones that we do not deem to be probable of being achieved, the associated milestone payments are fully constrained and the value of the milestone is excluded from the transaction price with no revenue being recognized. Milestone payments that are not within our control, such as regulatory-related accomplishments, are not considered probable of being achieved until those accomplishments have been communicated by the relevant regulatory authority. Once the assessment of probability of achievement becomes probable, we recognize revenue for the milestone payment under collaboration revenue. At each reporting period, we assess the probability of achievement of each milestone under our current agreements. Royalties . For agreements with sales-based royalties, including milestone payments based on the level of sales, where the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (a) when the related sales occur, or (b) when the performance obligation, to which some or all of the royalty has been allocated, has been satisfied (or partially satisfied). At each reporting period, we estimate the sales incurred by each licensee based on historical experience and accrue the associated royalty amount. Cost Sharing Arrangements . Research and development and other expenses being shared by both parties under an agreement are recorded as earned or owed based on the performance obligations by both parties under the respective agreement. 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 over time in a manner proportionate to the costs we incurred to perform the services using the input method.
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. 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 of clinical trial costs 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 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 included in operating expenses on our condensed statements of operations related to stock options and employee stock purchases for the three and six months ended June 30, 2018 and 2017 which was allocated as follows: Three Months Ended June 30, Six Months Ended June 30, (In thousands) 2018 2017 2018 2017 Research and development $ 266 $ 250 $ 421 $ 541 General and administrative 1,279 1,825 2,738 3,517 Stock-based compensation expense included in operating expenses $ 1,545 $ 2,075 $ 3,159 $ 4,058 As stock-based compensation expense recognized in our condensed statements of operations for the three and six months ended June 30, 2018 and 2017 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. Stock Options We grant options with service-based vesting under our equity plans to employees, non-employee directors and consultants. The vesting period for employee options is generally four years. The fair value of options granted during the six months ended June 30, 2018 and 2017 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.821 to 0.832 0.884 to 0.892 Risk-free interest rate range 2.55% to 2.94% 1.98% to 1.99% Expected term 5.25 yrs 5.5 yrs Employee Stock Purchase Plan The fair value of employees’ purchase rights during the six months ended June 30, 2018 and 2017 has been estimated using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.437 to 0.475 0.577 to 0.641 Risk-free interest rate range 1.53% to 1.76% 0.45% to 0.89% Expected term range 6 - 12 mos 6 - 12 mos Dividend yield is based on historical cash dividend payments. The expected volatility is based on historical volatilities of our stock since traded options on Geron stock do not correspond to option terms and the trading volume of options is limited. The risk-free interest rate 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. Non-Employee Stock-Based Awards 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 condensed statements of operations.
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	Recent Accounting Pronouncements New Accounting Pronouncements – Recently Adopted In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09, which amends the guidance for accounting for revenue from contracts with customers. This ASU superseded the revenue recognition requirements in Accounting Standards Codification Topic 605, Revenue Recognition We adopted Topic 606 on January 1, 2018 using the modified retrospective transition method for those agreements which were not completed as of January 1, 2018. Financial results for the reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts have not been adjusted and continue to be reported in accordance with our historical accounting under Topic 605. In connection with the adoption of Topic 606, we recognized a cumulative-effect adjustment to our opening balance of accumulated deficit and an increase to interest and other receivables of $204,000 as of January 1, 2018 for projected sales-based royalties on product sales occurring in 2017 for which payments had not yet been received as of December 31, 2017. Such royalties were recognized as revenue in prior periods when payments were received from our licensees. In accordance with Topic 606-10-50-14a, we have elected to exclude providing further information about our sales-based royalties. The adoption of Topic 606 did not result in any changes to the estimated transaction price or the performance obligations for current agreements or the amounts allocated to satisfied performance obligations. We do not have any deferred revenue associated with unsatisfied performance obligations. Since we view our operations as a single segment and all of our revenues are recognized at a point in time from similar license agreements, disaggregated revenue disclosures would not materially provide additional information. We do not expect the application of Topic 606 to have a material impact on our financial results on an ongoing basis in comparison to results that would have been realized if we had continued to apply Topic 605. In January 2016, the FASB issued ASU 2016-01 which requires equity investments to be measured at fair value with changes in fair value recognized in the statements of operations. To further clarify ASU 2016-01, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities in Sienna Cancer Diagnostics Limited, or Sienna we remeasured the fair value of our equity investment in Sienna at each reporting date in 2018 The cumulative-effect adjustments to our January 1, 2018 condensed balance sheet for the adoption of Topic 606 and ASU 2016-01 and ASU 2018-03 were as follows (in thousands): Condensed Balance Sheet Balance at December 31, 2017 Adjustments Due to Topic 606 Adjustments Due to ASU 2016-01 and ASU 2018-03 Balance at January 1, 2018 Assets: Interest and other receivables $ 436 $ 204 $ - $ 640 Other assets $ - $ - $ 1,189 $ 1,189 Stockholders’ Equity: Accumulated deficit $ (985,840 ) $ 204 $ 1,189 $ (984,447 ) As of January 1, 2018, we also adopted ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments Statement of Cash Flows (Topic 230) Restricted Cash Compensation — Stock Compensation: Scope of Modification Accounting New Accounting Pronouncements – Issued But Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting

SUMMARY OF SIGNIFICANT ACCOUN12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	6 Months Ended
	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards	The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options and employee stock purchases for the three and six months ended June 30, 2018 and 2017 which was allocated as follows: Three Months Ended June 30, Six Months Ended June 30, (In thousands) 2018 2017 2018 2017 Research and development $ 266 $ 250 $ 421 $ 541 General and administrative 1,279 1,825 2,738 3,517 Stock-based compensation expense included in operating expenses $ 1,545 $ 2,075 $ 3,159 $ 4,058
Schedule of assumptions used to estimate the fair value of stock options granted	The fair value of options granted during the six months ended June 30, 2018 and 2017 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.821 to 0.832 0.884 to 0.892 Risk-free interest rate range 2.55% to 2.94% 1.98% to 1.99% Expected term 5.25 yrs 5.5 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan	The fair value of employees’ purchase rights during the six months ended June 30, 2018 and 2017 has been estimated using the Black Scholes option-pricing model with the following assumptions: Six Months Ended June 30, 2018 2017 Dividend yield 0% 0% Expected volatility range 0.437 to 0.475 0.577 to 0.641 Risk-free interest rate range 1.53% to 1.76% 0.45% to 0.89% Expected term range 6 - 12 mos 6 - 12 mos
Schedule of cumulative effect adjustments for the adoption of Topic 606 and ASU 2016-01 and ASU 2018-03	The cumulative-effect adjustments to our January 1, 2018 condensed balance sheet for the adoption of Topic 606 and ASU 2016-01 and ASU 2018-03 were as follows (in thousands): Condensed Balance Sheet Balance at December 31, 2017 Adjustments Due to Topic 606 Adjustments Due to ASU 2016-01 and ASU 2018-03 Balance at January 1, 2018 Assets: Interest and other receivables $ 436 $ 204 $ - $ 640 Other assets $ - $ - $ 1,189 $ 1,189 Stockholders’ Equity: Accumulated deficit $ (985,840 ) $ 204 $ 1,189 $ (984,447 )

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	6 Months Ended
	Jun. 30, 2018
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 June 30, 2018 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 $ 11,450 $ - $ - $ 11,450 Commercial paper 5,689 1 (1 ) 5,689 $ 17,139 $ 1 $ (1 ) $ 17,139 Restricted cash: Certificate of deposit $ 269 $ - $ - $ 269 Marketable securities: Government-sponsored enterprise securities (due in less than one year) $ 10,000 $ - $ (10 ) $ 9,990 Commercial paper (due in less than one year) 56,917 181 (4 ) 57,094 Corporate notes (due in less than one year) 74,930 - (214 ) 74,716 Corporate notes (due in one to two years) 20,280 - (30 ) 20,250 $ 162,127 $ 181 $ (258 ) $ 162,050 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
Schedule of cash equivalents and marketable securities with unrealized losses	Cash equivalents and marketable securities with unrealized losses that have been in a continuous unrealized loss position for less than 12 months and 12 months or longer at June 30, 2018 and December 31, 2017 were as follows: Less Than 12 Months 12 Months or Longer Total Gross Gross Gross Estimated Unrealized Estimated Unrealized Estimated Unrealized (In thousands) Fair Value Losses Fair Value Losses Fair Value Losses As of June 30, 2018: Government-sponsored enterprise securities (due in less than one year) $ - $ - $ 9,990 $ (10 ) $ 9,990 $ (10 ) Commercial paper (due in less than one year) 10,639 (5 ) - - 10,639 (5 ) Corporate notes (due in less than one year) 62,975 (184 ) 10,241 (30 ) 73,216 (214 ) Corporate notes (due in one to two years) 20,250 (30 ) - - 20,250 (30 ) $ 93,864 $ (219 ) $ 20,231 $ (40 ) $ 114,095 $ (259 ) 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 )
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 June 30, 2018 and December 31, 2017 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 June 30, 2018: Money market funds (1) $ 11,450 $ - $ - $ 11,450 Government-sponsored enterprise securities (2) - 9,990 - 9,990 Commercial paper (1)(2) - 62,783 - 62,783 Corporate notes (2)(3) - 94,966 - 94,966 Equity investment (4) - 676 - 676 Total $ 11,450 $ 168,415 $ - $ 179,865 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 (1) Included in cash and cash equivalents on our condensed balance sheets. (2) Included in current portion of marketable securities on our condensed balance sheets. (3) Included in noncurrent portion of marketable securities on our condensed balance sheets. (4) Included in other assets on our condensed balance sheets. See “Equity Investment” in this Note 2 on Fair Value Measurements for further discussion of this equity investment.

SUMMARY OF SIGNIFICANT ACCOUN14

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ANTI-DILUTIVE SHARES (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock options and warrants 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)	26,306,263	23,044,422	26,306,263	23,044,422

SUMMARY OF SIGNIFICANT ACCOUN15

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - USEFUL LIVES OF ASSETS (Details)	6 Months Ended
	Jun. 30, 2018
Depreciation [Abstract]
Estimated useful lives of assets	4 years

SUMMARY OF SIGNIFICANT ACCOUN16

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - STOCK BASED COMPENSATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 1,545	$ 2,075	$ 3,159	$ 4,058
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	266	250	421	541
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$ 1,279	$ 1,825	$ 2,738	$ 3,517

SUMMARY OF SIGNIFICANT ACCOUN17

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - STOCK OPTIONS AND EMPLOYEE STOCK PURCHASE PLAN (Details)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stock Options
Stock-Based Compensation
Vesting period of awards	4 years
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%
Expected volatility range, minimum (as a percent)	82.10%	88.40%
Expected volatility range, maximum (as a percent)	83.20%	89.20%
Risk-free interest rate range, minimum (as a percent)	2.55%	1.98%
Risk-free interest rate range, maximum (as a percent)	2.94%	1.99%
Expected term	5 years 3 months	5 years 6 months
Employee Stock Purchase Plan
Assumptions used to estimate fair value of awards
Dividend yield (as a percent)	0.00%	0.00%
Expected volatility range, minimum (as a percent)	43.70%	57.70%
Expected volatility range, maximum (as a percent)	47.50%	64.10%
Risk-free interest rate range, minimum (as a percent)	1.53%	0.45%
Risk-free interest rate range, maximum (as a percent)	1.76%	0.89%
Employee Stock Purchase Plan | Minimum
Assumptions used to estimate fair value of awards
Expected term	6 months	6 months
Employee Stock Purchase Plan | Maximum
Assumptions used to estimate fair value of awards
Expected term	12 months	12 months

SUMMARY OF SIGNIFICANT ACCOUN18

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CUMULATIVE EFFECT ADJUSTMENT (Details) $ in Thousands	Jan. 01, 2018USD ($)
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Adjustment to accumulated deficit	$ 204

SUMMARY OF SIGNIFICANT ACCOUN19

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CUMULATIVE EFFECT ADJUSTMENTS FOR THE ADOPTION OF TOPIC 606 AND ASU 2016-01 AND ASU 2018-03 (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Interest and other receivables	$ 773	$ 640	$ 436
Other assets	676	1,189
Stockholders' equity:
Accumulated deficit	$ (998,567)	(984,447)	$ (985,840)
ASU 2014-09 | Adjustments Due to Topic 606
ASSETS
Interest and other receivables		204
Stockholders' equity:
Accumulated deficit		204
Adjustments Due to ASU 2016-01 and ASU 2018-03
ASSETS
Other assets		1,189
Stockholders' equity:
Accumulated deficit		$ 1,189

FAIR VALUE MEASUREMENTS - SECUR

FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Included in cash and cash equivalents:
Amortized Cost	$ 17,139	$ 15,022
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	17,139	15,021
Restricted cash:
Amortized Cost	269	268
Marketable securities:
Amortized Cost	162,127	92,798
Gross Unrealized Gains	181	4
Gross Unrealized Losses	(258)	(210)
Estimated Fair Value	162,050	92,592
Money market funds
Included in cash and cash equivalents:
Amortized Cost	11,450	11,030
Estimated Fair Value	11,450	11,030
Commercial paper
Included in cash and cash equivalents:
Amortized Cost	5,689	2,242
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)
Estimated Fair Value	5,689	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	269	268
Estimated Fair Value	269	268
Government-sponsored enterprise securities (due in less than one year)
Marketable securities:
Amortized Cost	10,000	12,500
Gross Unrealized Losses	(10)	(40)
Estimated Fair Value	9,990	12,460
Commercial paper (due in less than one year)
Marketable securities:
Amortized Cost	56,917	10,928
Gross Unrealized Gains	181	4
Gross Unrealized Losses	(4)	(1)
Estimated Fair Value	57,094	10,931
Corporate notes (due in less than one year)
Marketable securities:
Amortized Cost	74,930	55,067
Gross Unrealized Losses	(214)	(107)
Estimated Fair Value	74,716	54,960
Corporate notes (due in one to two years)
Marketable securities:
Amortized Cost	20,280	14,303
Gross Unrealized Losses	(30)	(62)
Estimated Fair Value	$ 20,250	$ 14,241

FAIR VALUE MEASUREMENTS - SEC21

FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 93,864	$ 77,168
Less Than 12 Months - Gross Unrealized Losses	(219)	(169)
12 Months or Longer - Estimated Fair Value	20,231	13,959
12 Months or Longer - Gross Unrealized Losses	(40)	(42)
Total - Estimated Fair Value	114,095	91,127
Total - Gross Unrealized Losses	(259)	(211)
Government-sponsored enterprise securities (due in less than one year)
Available for sale securities with unrealized losses
12 Months or Longer - Estimated Fair Value	9,990	12,460
12 Months or Longer - Gross Unrealized Losses	(10)	(40)
Total - Estimated Fair Value	9,990	12,460
Total - Gross Unrealized Losses	(10)	(40)
Commercial paper (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	10,639	7,717
Less Than 12 Months - Gross Unrealized Losses	(5)	(1)
Total - Estimated Fair Value	10,639	7,717
Total - Gross Unrealized Losses	(5)	(1)
Corporate notes (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	62,975	55,210
Less Than 12 Months - Gross Unrealized Losses	(184)	(106)
12 Months or Longer - Estimated Fair Value	10,241	1,499
12 Months or Longer - Gross Unrealized Losses	(30)	(2)
Total - Estimated Fair Value	73,216	56,709
Total - Gross Unrealized Losses	(214)	(108)
Corporate notes (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	20,250	14,241
Less Than 12 Months - Gross Unrealized Losses	(30)	(62)
Total - Estimated Fair Value	20,250	14,241
Total - Gross Unrealized Losses	$ (30)	$ (62)

FAIR VALUE MEASUREMENTS - RECUR

FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value on a Recurring Basis
Total	$ 179,865	$ 107,613
Money market funds
Fair Value on a Recurring Basis
Total	11,450	11,030
Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	9,990	12,460
Commercial paper
Fair Value on a Recurring Basis
Total	62,783	13,173
Corporate notes
Fair Value on a Recurring Basis
Total	94,966	70,950
Equity Investment
Fair Value on a Recurring Basis
Total	676
Level 1
Fair Value on a Recurring Basis
Total	11,450	11,030
Level 1 | Money market funds
Fair Value on a Recurring Basis
Total	11,450	11,030
Level 2
Fair Value on a Recurring Basis
Total	168,415	96,583
Level 2 | Government-sponsored enterprise securities
Fair Value on a Recurring Basis
Total	9,990	12,460
Level 2 | Commercial paper
Fair Value on a Recurring Basis
Total	62,783	13,173
Level 2 | Corporate notes
Fair Value on a Recurring Basis
Total	94,966	$ 70,950
Level 2 | Equity Investment
Fair Value on a Recurring Basis
Total	$ 676

FAIR VALUE MEASUREMENTS - EQUIT

FAIR VALUE MEASUREMENTS - EQUITY INVESTMENT (Details) - Sienna - Equity Investment - USD ($)	Aug. 03, 2017	Jun. 30, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2007
Equity Investments [Line Item]
Number of shares owned						13,842,625
Cost method investment, original cost					$ 0	$ 0
Trading restriction period	24 months
Fair value of equity investment		$ 676,000	$ 676,000
Change in fair value of equity investment		388,000	513,000
Loss related to foreign currency translation		$ 38,000	$ 38,000
Accounting Standards Update 2016-01 and 2018-03
Equity Investments [Line Item]
Cumulative effect adjustment				$ 1,189,000

COLLABORATION AGREEMENT (Detail

COLLABORATION AGREEMENT (Details)	Dec. 15, 2014USD ($)item	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements [Line Items]
Accrued collaboration charges		$ 2,192,000	$ 1,702,000
Janssen Biotech | Collaboration Agreement
Collaborative Arrangements [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		$ 2,192,000
Janssen Biotech | Collaborative Arrangement IP Exclusively Licensed
Collaborative Arrangements [Line Items]
Percentage of costs to be paid by Geron	50.00%
Percentage of costs to be paid by Janssen	50.00%
Janssen Biotech | U.S. Opt-In Rights Exercised Collaboration Agreement
Collaborative Arrangements [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	mid-teens
Tiered royalties percentage, high end of the range	low twenties
U.S. selling effort percentage	20.00%
Janssen Biotech | U.S. Opt-In Rights Not Exercised Collaboration Agreement
Collaborative Arrangements [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
Tiered royalties percentage, low end of the range	double-digit
Tiered royalties percentage, high end of the range	mid-teens
Full U.S. Rights fee	$ 70,000,000

STOCKHOLDERS' EQUITY - AT MARKE

STOCKHOLDERS' EQUITY - AT MARKET ISSUANCE SALES AGREEMENTS (Details) - USD ($)	May 18, 2018	Aug. 28, 2015	Jun. 30, 2018	Jun. 30, 2018
2015 Sales Agreement
At Market Issuance Sales Agreements [Line Items]
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 (in shares)				13,195,106
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs				$ 47,651,000
2018 Sales Agreement
At Market Issuance Sales Agreements [Line Items]
Aggregate offering price of common stock	$ 100,000,000
Maximum commission rate (as a percent)	3.00%
Issuance of common stock in connection with at market offering (in shares)			9,447,026
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs			$ 36,208,000

STOCKHOLDERS' EQUITY - 2018 EQU

STOCKHOLDERS' EQUITY - 2018 EQUITY INCENTIVE PLAN (Details)	May 15, 2018shares
2018 Plan
Stockholder's Equity [Line Items]
Common stock, shares newly reserved for future issuance	10,000,000

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($)	1 Months Ended	3 Months Ended
	Jul. 31, 2018	Jun. 30, 2018
2018 Sales Agreement
Subsequent Event [Line Items]
Issuance of common stock in connection with at market offering (in shares)		9,447,026
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs		$ 36,208,000
Subsequent Event | 2011 Plan
Subsequent Event [Line Items]
Options exercised (in shares)	438,902
Options exercised, weighted average exercise price per share (in dollars per share)	$ 1.71
Cash proceeds from stock options exercised	$ 749,000
Subsequent Event | 2018 Sales Agreement
Subsequent Event [Line Items]
Issuance of common stock in connection with at market offering (in shares)	636,053
Net cash proceeds from issuance of common stock after deducting sales commissions and offering costs	$ 2,167,000