Geron (GERN) 10-K 11 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Mar. 06, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	GERON CORP
Entity Central Index Key	886744
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$501,005,000
Entity Common Stock, Shares Outstanding		157,700,375
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$42,796	$12,990
Restricted cash	266	795
Marketable securities	108,645	52,234
Interest and other receivables	963	564
Prepaid assets	736	474
Total current assets	153,406	67,057
Noncurrent marketable securities	18,932
Property and equipment, net	173	92
Deposits and other assets		195
Total assets	172,511	67,344
Current liabilities:
Accounts payable	1,033	1,397
Accrued compensation and benefits	4,213	3,946
Accrued restructuring charges		94
Accrued liabilities	1,537	1,783
Deferred revenue	35,000
Fair value of derivatives	16	367
Total current liabilities	41,799	7,587
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 3,000,000 shares authorized; no shares issued and outstanding at December 31, 2014 and 2013
Common Stock, $0.001 par value; 300,000,000 shares authorized; 157,429,871 and 130,677,949 shares issued and outstanding at December 31, 2014 and 2013, respectively	157	131
Additional paid-in capital	1,059,072	952,403
Accumulated deficit	-928,433	-892,763
Accumulated other comprehensive loss	-84	-14
Total stockholders' equity	130,712	59,757
Total liabilities and stockholders' equity	$172,511	$67,344

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$0.00	$0.00
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)	$0.00	$0.00
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	157,429,871	130,677,949
Common stock, shares outstanding	157,429,871	130,677,949

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENTS OF OPERATIONS
License fees and royalties	$1,153,000	$1,283,000	$2,709,000
Operating expenses:
Research and development	20,707,000	23,155,000	51,368,000
Restructuring charges		1,462,000	2,702,000
General and administrative	16,758,000	15,624,000	20,397,000
Total operating expenses	37,465,000	40,241,000	74,467,000
Loss from operations	-36,312,000	-38,958,000	-71,758,000
Unrealized gain (loss) on derivatives	351,000	-316,000	13,000
Interest and other income	373,000	951,000	3,097,000
Interest and other expense	-82,000	-56,000	-233,000
Net loss	($35,670,000)	($38,379,000)	($68,881,000)
Basic and diluted net loss per share (in dollars per share)	($0.23)	($0.30)	($0.54)
Shares used in computing basic and diluted net loss per share (in shares)	153,540,341	128,380,800	126,941,024

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS
Net loss	($35,670)	($38,379)	($68,881)
Other comprehensive income (loss):
Net unrealized loss on marketable securities	-70	-54	-38
Foreign currency translation adjustments			16
Reclassification of accumulated foreign currency translation adjustments			153
Other comprehensive (loss) income	-70	-54	131
Comprehensive loss	($35,740)	($38,433)	($68,750)

CONSOLIDATED_STATEMENTS_OF_STO

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balances at Dec. 31, 2011	$131,000	$932,066,000	($785,503,000)	($91,000)	$146,603,000
Balances (in shares) at Dec. 31, 2011	131,443,148
Increase (Decrease) in Stockholders' Equity
Net loss			-68,881,000		-68,881,000
Other comprehensive income (loss)				131,000	131,000
Stock-based compensation related to issuance of common stock and options in exchange for services		135,000			135,000
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)	170,298
Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock	-2,000	269,000			267,000
Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock (in shares)	-2,592,375
Stock-based compensation for equity-based awards to employees and directors		5,311,000			5,311,000
401(k) contribution	1,000	2,086,000			2,087,000
401(k) contribution (in shares)	1,221,624
Balances at Dec. 31, 2012	130,000	939,867,000	-854,384,000	40,000	85,653,000
Balances (in shares) at Dec. 31, 2012	130,242,695
Increase (Decrease) in Stockholders' Equity
Net loss			-38,379,000		-38,379,000
Other comprehensive income (loss)				-54,000	-54,000
Stock-based compensation related to issuance of common stock and options in exchange for services		252,000			252,000
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)	66,853
Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock		6,553,000			6,553,000
Cancellations of non-vested restricted stock under equity plans, net of issuances of common stock (in shares)	-388,056
Stock-based compensation for equity-based awards to employees and directors		4,435,000			4,435,000
401(k) contribution	1,000	1,296,000			1,297,000
401(k) contribution (in shares)	756,457
Balances at Dec. 31, 2013	131,000	952,403,000	-892,763,000	-14,000	59,757,000
Balances (in shares) at Dec. 31, 2013	130,677,949				130,677,949
Increase (Decrease) in Stockholders' Equity
Net loss			-35,670,000		-35,670,000
Other comprehensive income (loss)				-70,000	-70,000
Issuance of common stock in connection with public offering, net of issuance costs of $6,695,000	26,000	96,779,000			96,805,000
Issuance of common stock in connection with public offering, net of issuance costs (in shares)	25,875,000
Stock-based compensation related to issuance of common stock and options in exchange for services		253,000			253,000
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)	71,239
Issuance of common stock upon net exercise of warrants (in shares)	168,039
Issuance of common stock under equity plans, net of cancellations of non-vested restricted stock		1,555,000			1,555,000
Issuance of common stock under equity plans, net of cancellations of non-vested restricted stock (in shares)	564,950
Stock-based compensation for equity-based awards to employees and directors		7,658,000			7,658,000
401(k) contribution		424,000			424,000
401(k) contribution (in shares)	72,694
Balances at Dec. 31, 2014	$157,000	$1,059,072,000	($928,433,000)	($84,000)	$130,712,000
Balances (in shares) at Dec. 31, 2014	157,429,871				157,429,871

CONSOLIDATED_STATEMENTS_OF_STO1

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Issuance costs	$6,695

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	($35,670)	($38,379)	($68,881)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	47	320	830
Accretion and amortization on investments, net	2,889	1,322	2,184
Loss (gain) on retirement/sales of property and equipment, net	3	-831	-142
Loss on write-downs of property and equipment		200	271
Stock-based compensation for services by non-employees	253	252	183
Stock-based compensation for employees and directors	7,658	4,435	5,311
Amortization related to 401(k) contributions	111	458	726
Unrealized (gain) loss on derivatives	-351	316	-13
Changes in assets and liabilities:
Interest and other receivables	-399	188	646
Prepaid assets	-72	1,081	1,311
Deposits and other assets	5	-4	112
Accounts payable	-364	-2,032	449
Accrued compensation and benefits	580	-431	3,548
Accrued restructuring charges	-94	-1,878	-1,758
Accrued liabilities	-246	-1,697	-92
Deferred revenue	35,000
Translation adjustment			169
Net cash provided by (used in) operating activities	9,350	-36,680	-55,146
Cash flows from investing activities:
Restricted cash transfer	529	-1	-1
Purchases of property and equipment	-131	-3	-862
Proceeds from sales of property and equipment		1,196	170
Purchases of marketable securities	-190,263	-88,977	-79,369
Proceeds from sales/calls of marketable securities	10,549
Proceeds from maturities of marketable securities	101,412	108,839	141,016
Net cash (used in) provided by investing activities	-77,904	21,054	60,954
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	98,360	6,553	150
Net cash provided by financing activities	98,360	6,553	150
Net increase (decrease) in cash and cash equivalents	29,806	-9,073	5,958
Cash and cash equivalents, at beginning of year	12,990	22,063	16,105
Cash and cash equivalents, at end of year	$42,796	$12,990	$22,063

ORGANIZATION_AND_SUMMARY_OF_SI

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2014
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
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 clinical stage biopharmaceutical company focused on the development of a telomerase inhibitor, imetelstat, in hematologic myeloid malignancies. 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 Biotech, Inc., or Janssen, to develop and commercialize imetelstat worldwide for oncology, including hematologic myeloid malignancies, and all other human therapeutic uses. The significance of future losses will depend on whether Janssen continues to develop and advance imetelstat and the clinical and commercial success of imetelstat, which would result in future revenues to us in the form of milestone payments and royalties under the Collaboration Agreement, as described below, and whether we acquire other oncology products, programs or companies to diversify our business. There can be no assurance that we will receive any milestone payments or royalties from Janssen in the future. Imetelstat, which is our sole product candidate, will require significant additional clinical testing prior to possible regulatory approval in the United States and other countries, and we do not expect imetelstat to be commercially available for many years, if at all.
	Principles of Consolidation
	The consolidated financial statements include the accounts of Geron and our former wholly-owned subsidiary, Geron Bio-Med Ltd. (Geron Bio-Med), a United Kingdom company. In March 2012, the board of directors and shareholders of Geron Bio-Med approved actions to commence a voluntary winding up of the company. The full wind up of Geron Bio-Med was completed in August 2012. Prior to 2013, we eliminated intercompany accounts and transactions and prepared the financial statements of Geron Bio-Med using the local currency as the functional currency. We translated the assets and liabilities of Geron Bio-Med at rates of exchange at the balance sheet date and translated income and expense items at average monthly rates of exchange. The resultant translation adjustments were included in accumulated other comprehensive income (loss), a separate component of stockholders' equity.
	Net Loss Per Share
	Basic earnings (loss) per share is calculated based on the weighted average number of shares of common stock outstanding during the period. Diluted earnings (loss) per share is calculated based on the weighted average number of shares of common stock and potential dilutive securities outstanding during the period. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase common stock and are determined using the treasury stock method at an average market price during the period.
	Because we are in a net loss position, diluted loss per share excludes the effects of potential dilutive securities. Had we been in a net income position, diluted earnings per share would have included the shares used in the computation of basic net loss per share as well as an additional 3,072,340, 532,120 and 11,497 shares for 2014, 2013 and 2012, respectively, related to outstanding stock options, restricted stock awards and warrants (as determined using the treasury stock method at the estimated average market value).
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On a regular basis, management evaluates these estimates and assumptions. 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. Our marketable securities include U.S. government-sponsored enterprise securities, commercial paper and corporate notes with original maturities ranging from four to 19 months.
	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 consolidated 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 associated with credit losses judged as other-than-temporary result in a charge to interest and other income. Other-than-temporary charges not related to credit losses are included in accumulated other comprehensive income (loss) in stockholders' equity. We have not recorded any other-than-temporary impairment charges for our available-for-sale securities for the years ended December 31, 2014, 2013 and 2012. See Note 2 on Fair Value Measurements.
	Non-Marketable Equity Investments
	Non-marketable equity investments in companies in which we own less than 20% of the outstanding voting stock and do not otherwise have the ability to exert significant influence over the investees are carried at cost, as adjusted for other-than-temporary impairments. We apply the equity method of accounting for investments in non-marketable nonpublic companies in which we own more than 20% of the outstanding voting stock or otherwise have the ability to exert significant influence over the investees. Under this method, we increase (decrease) the carrying value of our investment by a proportionate share of the investee's earnings (losses). If losses exceed the carrying value of the investment, losses are then applied against any advances to the investee, including any commitment to provide financial support, until those amounts are reduced to zero. Commitments to provide financial support include formal guarantees, implicit arrangements, reputational expectations, intercompany relationships or a consistent past history of providing financial support. The equity method is then suspended until the investee has earnings. Any proportionate share of investee earnings is first applied to the share of accumulated losses not recognized during the period the equity method was suspended. We recognize previously suspended losses to the extent additional investment is determined to represent the funding of prior losses. See Note 7 on Divestiture of Stem Cell Assets.
	Fair Value of Derivatives
	For non-employee options classified as liabilities, the fair value of these instruments is recorded on the consolidated balance sheet at inception and adjusted to fair value at each financial reporting date. The change in fair value of the non-employee options is recorded in the consolidated statements of operations as unrealized gain (loss) on derivatives. Fair value of non-employee options is estimated using the Black Scholes option-pricing model. The non-employee options continue to be reported as a liability until such time as the instruments are exercised or expire or are otherwise modified to remove the provisions which require this treatment, at which time these instruments are marked to fair value and reclassified from liabilities to stockholders' equity. For non-employee options classified as permanent equity, the fair value of the non-employee options is recorded in stockholders' equity as of their respective vesting dates and no further adjustments are made. See Note 2 on Fair Value Measurements.
	Nonmonetary Transactions
	We account for nonmonetary transactions based on the fair values of the assets (or services) involved. The cost of a nonmonetary asset acquired in exchange for another nonmonetary asset is the fair value of the asset surrendered to obtain it with a gain or loss recognized on the exchange. We use the fair value of the asset received to measure the cost if it is more clearly evident than the fair value of the asset surrendered. If the fair value of neither the assets received nor the assets relinquished is determinable within reasonable limits, we use the recorded amount (or carrying value) of the nonmonetary assets relinquished to account for the exchange. Similarly, we use carrying value for an exchange of controlled assets that do not meet the definition of a business for a non-controlling non-marketable equity interest in a company with no gain or loss recognized on the exchange. See Note 7 on Divestiture of Stem Cell Assets.
	Revenue Recognition
	In general, 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 with Janssen, 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 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: (1) the deliverables included in the arrangement and (2) 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 if (ii) 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 and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner 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, related to a license that has standalone value from the other deliverables to be provided under the agreement, have been delivered 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.
	At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the 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 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.
	Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured. If royalties cannot be reasonably estimated or collectability of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments will be accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.
	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 depending 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 depending 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 separate certificate of deposit accounts for specified purposes. The components of restricted cash were as follows:
		December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases		266			265
		$	266		$	795
	In 2014, we closed the certificate of deposit for our unused equipment line of credit upon maturity and transferred the cash proceeds to our cash operating accounts. This action also cancelled the availability of the equipment line of credit.
	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 and research-related overhead. Research and development costs are expensed as incurred, including payments made under our license agreements.
	Clinical Trial Costs
	A significant component of our research and development expenses has historically been clinical trial costs. Substantial portions of our preclinical studies and all of our clinical trials have been performed by third-party contract research organizations, or CROs, and other vendors. We accrue expenses for preclinical studies performed by our vendors based on certain estimates over the term of the service period and adjust our estimates as required. We accrue expenses for clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, the number of active clinical sites and the duration for which the patients will be enrolled in the study. Pass through costs from CROs include, but are not limited to, regulatory expenses, investigator fees, lab fees, travel costs and other miscellaneous costs, including shipping and printing fees. We accrue pass through costs based on estimates of the amount of work completed for the clinical trial. We monitor patient enrollment levels and related activities to the extent possible through internal reviews, review of contractual terms and correspondence with CROs. We 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 on a straight-line basis over the requisite service period, which is generally the vesting period. For additional information, see Note 9 on Stockholders' Equity.
	Stock Options and Employee Stock Purchase Plan
	We grant service-based stock options under our equity plans to employees, directors and consultants. The vesting period for employee options is generally four years. We use the Black Scholes option-pricing model to estimate the grant-date fair value of our stock options and employee stock plan purchases. The determination of fair value for these stock-based awards on the date of grant 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. For additional information, see Note 9 on Stockholders' Equity.
	Restricted Stock Awards
	We have granted restricted stock awards to employees and directors with three types of vesting schedules: (i) service-based, (ii) performance-based or (iii) market-based. Service-based restricted stock awards generally vest annually over four years. Performance-based restricted stock awards vest upon achievement of discrete strategic corporate goals within a specified performance period, generally three years. Market-based restricted stock awards vest only upon achievement of certain market price thresholds of our common stock within a specified performance period, generally three years.
	The fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. The fair value is amortized as stock-based compensation expense over the requisite service period of the award, which is generally the vesting period, on a straight-line basis and is reduced for estimated forfeitures, as applicable.
	The fair value for performance-based restricted stock awards is determined using the fair value of our common stock on the date of grant. Stock-based compensation expense for awards with vesting based on performance conditions is recognized over the period from the date the performance condition is determined to be probable of occurring through the date the applicable condition is expected to be met and is reduced for estimated forfeitures, as applicable. If the performance condition is not considered probable of being achieved, no stock-based compensation expense is recognized until such time as the performance condition is considered probable of being met, if at all. If that assessment of the probability of the performance condition being met changes, the impact of the change in estimate would be recognized in the period of the change. If the requisite service period has been met prior to the change in estimate, the effect of the change in estimate would be recognized immediately. All previously granted performance-based restricted stock awards have been cancelled unvested as the performance conditions were not achieved within the respective performance periods.
	The fair value for market-based restricted stock awards is determined using a lattice valuation model with a Monte Carlo simulation. The model takes into consideration the historical volatility of our stock and the risk-free interest rate at the date of grant. In addition, the model is used to estimate the derived service period for the awards. The derived service period is the estimated period of time that would be required to satisfy the market condition, assuming the market condition will be satisfied. Stock-based compensation expense is recognized over the derived service period for the awards using the straight-line method and is reduced for estimated forfeitures, as applicable, but is accelerated if the market condition is achieved earlier than estimated. If a market-based restricted stock award is forfeited or expires after completion of the derived service period, any previously recognized stock-based compensation expense is not reversed. All previously granted market-based restricted stock awards have been cancelled unvested as the market conditions were not achieved within the specified performance 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 awards in our consolidated statements of operations.
	Accumulated Other Comprehensive Loss
	Accumulated other comprehensive loss includes certain changes in stockholders' equity which are excluded from net loss. The components of accumulated other comprehensive loss were as follows:
		December 31,
	(In thousands)	2014			2013
	Unrealized loss on marketable securities	$	(84	)	$	(14	)
	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 within operations would be recorded as income tax expense.
	Concentrations of Customers and Suppliers
	The majority of our revenues was earned in the United States. Two customers accounted for approximately 31%, 42% and 59% of our 2014, 2013 and 2012 revenues, respectively.
We contract third-party manufacturers to produce GMP-grade drugs for preclinical and clinical studies. We also contract for starting materials to supply those manufacturers and us. Certain development and clinical activities may be delayed if we or Janssen are unable to obtain sufficient quantities of starting materials or GMP-grade drugs from current third-party suppliers or other third-party sources.
Recent Accounting Pronouncements
In April 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2014-08, Presentation of Financial Statements and Property, Plant, and Equipment: Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 raised the threshold for a disposal of assets to qualify as a discontinued operation and requires new disclosures for both discontinued operations and disposals of individually significant components of a business that do not qualify as discontinued operations. Under the new guidance, only disposals of assets representing a strategic shift in operations that has a major effect on the entity's operations and financial results should be presented as discontinued operations. If the disposal does qualify as a discontinued operation, the entity will be required to provide expanded disclosures, as well as disclosure of the pretax income attributable to the disposal of a significant part of an entity that does not qualify as a discontinued operation. ASU 2014-08 is effective for us beginning January 1, 2015 and subsequent interim periods. We do not expect the adoption of ASU 2014-08 to have a material effect on our consolidated financial statements.
In May 2014, the FASB issued Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers, or ASU 2014-09. ASU 2014-09 provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 will require an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This update creates a five-step model that requires entities to exercise judgment when considering the terms of the contract(s). The five-step model includes: (i) identifying the contract(s) with the customer, (ii) identifying the separate performance obligations in the contract, (iii) determining the transaction price, (iv) allocating the transaction price to the separate performance obligations, and (v) recognizing revenue when each performance obligation is satisfied. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 will be effective for us beginning January 1, 2017 and subsequent interim periods. We have the option to apply the provisions of ASU 2014-09 either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of applying this accounting standard recognized at the date of initial application. Early adoption is not permitted. We are currently evaluating the transition method and the impact that the adoption of ASU 2014-09 will have on our consolidated financial statements and related disclosures.
In August 2014, the FASB issued Accounting Standard Update No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern, or ASU 2014-15. ASU 2014-15 is intended to define management's responsibility to evaluate whether there is substantial doubt about an organization's ability to continue as a going concern and to provide related footnote disclosures. Substantial doubt about an entity's ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 provides guidance to an organization's management, with principles and definitions that are intended to reduce diversity in the timing and content of disclosures that are commonly provided by organizations in financial statement footnotes. ASU 2014-15 will be effective for us beginning December 31, 2016 and subsequent interim periods. Early adoption is permitted. We are currently in the process of evaluating the impact of adoption of ASU 2014-15 on our consolidated financial statements and related disclosures.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS
	2. FAIR VALUE MEASUREMENTS
	We categorize financial instruments recorded at fair value on our consolidated 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.
	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 consolidated balance sheets, including the category for such financial instruments.
	Cash Equivalents and Marketable Securities Available-for-Sale
	Certificates of deposit and 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.
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2014 were as follows:
	(In thousands)		Amortized Cost			Gross Unrealized Gains			Gross Unrealized Losses			Estimated Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	40,342		$	—		$	—		$	40,342
	Restricted cash:
	Certificate of deposit		$	266		$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401		$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)			6,556			—			(7	)		6,549
	Commercial paper (due in less than 1 year)			10,985			14			—			10,999
	Corporate notes (due in less than 1 year)			97,307			2			(63	)		97,246
	Corporate notes (due in 1 to 2 years)			12,412			—			(29	)		12,383
			$	127,661		$	16		$	(100	)	$	127,577
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2013 were as follows:
	(In thousands)		Amortized Cost			Gross Unrealized Gains			Gross Unrealized Losses			Estimated Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	8,079		$	—		$	—		$	8,079
	Corporate notes			2,206			—			—			2,206
			$	10,285		$	—		$	—		$	10,285
	Restricted cash:
	Certificates of deposit		$	795		$	—		$	—		$	795
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	7,369		$	1		$	(1	)	$	7,369
	Commercial paper (due in less than 1 year)			5,496			3			—			5,499
	Corporate notes (due in less than 1 year)			39,383			1			(18	)		39,366
			$	52,248		$	5		$	(19	)	$	52,234
	Marketable securities with unrealized losses at December 31, 2014 and 2013 were as follows:
			Less Than 12 Months						12 Months or Greater						Total
	(In thousands)		Estimated Fair Value			Gross Unrealized Losses			Estimated Fair Value			Gross Unrealized Losses			Estimated Fair Value			Gross Unrealized Losses
	As of December 31, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400		$	(1	)	$	—		$	—		$	400		$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)			5,549			(7	)		—			—			5,549			(7	)
	Corporate notes (due in less than 1 year)			92,989			(63	)		—			—			92,989			(63	)
	Corporate notes (due in 1 to 2 years)			12,383			(29	)		—			—			12,383			(29	)
			$	111,321		$	(100	)	$	—		$	—		$	111,321		$	(100	)
	As of December 31, 2013:
	Government-sponsored enterprise securities (due in less than 1 year)		$	3,947		$	(1	)	$	—		$	—		$	3,947		$	(1	)
	Corporate notes (due in less than 1 year)			37,060			(18	)		—			—			37,060			(18	)
			$	41,007		$	(19	)	$	—		$	—		$	41,007		$	(19	)
	The gross unrealized losses related to government-sponsored enterprise securities and corporate notes as of December 31, 2014 and 2013 were due to changes in interest rates. We determined that the gross unrealized losses on our marketable securities as of December 31, 2014 and 2013 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 basis.
	Derivatives
	Non-employee options are normally traded less actively, have trade activity that is one way, and/or are traded in less-developed markets and are therefore valued based upon models with significant unobservable market parameters, resulting in Level 3 categorization.
	Options held by non-employees whose performance obligations are complete are classified as derivative liabilities on our consolidated balance sheets. These options are marked to fair value at each reporting period, and upon the exercise of these options, the instruments are marked to fair value and reclassified from derivative liabilities to stockholders' equity. We have not recorded any reclassifications from current liabilities to stockholders' equity for non-employee option exercises in 2014 and 2013.
	As of December 31, 2014 and 2013, the following non-employee options to purchase common stock were considered derivatives and classified as current liabilities:
						Number of Shares at December 31,										Fair Value at December 31,
			Exercise									Exercisable		Expiration
	Issuance Date		Price			2014			2013			Date		Date		2014			2013
																(In thousands)
	Mar-05		$	6.39			284,600			284,600		Jan-07		Mar-15		$	16		$	367
	The fair value of derivatives has been calculated at each reporting date using the Black Scholes option-pricing model with the following assumptions:
			December 31,
			2014		2013
	Dividend yield		0%		0%
	Expected volatility		0.895		0.844
	Risk-free interest rate		0.04%		0.13%
Expected term		0.25 yr		1 yr
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 common stock do not correspond to derivatives' terms and trading volume of Geron 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 reporting date. The expected term of derivatives is equal to the remaining contractual term of the instruments.
Fair Value on a 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, 2014 and indicates the fair value category assigned.
		Fair Value Measurements at Reporting Date Using
		Quoted Prices in			Significant			Significant
		Active Markets for			Other			Unobservable
		Identical Assets /			Observable			Inputs
		Liabilities			Inputs
(In thousands)		Level 1			Level 2			Level 3			Total
Assets
Money market funds(1)		$	40,342		$	—		$	—		$	40,342
Government-sponsored enterprise securities(2)(3)			—			6,949			—			6,949
Commercial paper(2)			—			10,999			—			10,999
Corporate notes(2)(3)			—			109,629			—			109,629
Total		$	40,342		$	127,577		$	—		$	167,919
Liabilities
Derivatives(4)		$	—		$	—		$	16		$	16
The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2013 and indicates the fair value category assigned.
		Fair Value Measurements at Reporting Date Using
		Quoted Prices in			Significant			Significant
		Active Markets for			Other			Unobservable
		Identical Assets /			Observable			Inputs
		Liabilities			Inputs
(In thousands)		Level 1			Level 2			Level 3			Total
Assets
Money market funds(1)		$	8,079		$	—		$	—		$	8,079
Government-sponsored enterprise securities(2)			—			7,369			—			7,369
Commercial paper(2)			—			5,499			—			5,499
Corporate notes(1)(2)			—			41,572			—			41,572
Total		$	8,079		$	54,440		$	—		$	62,519
Liabilities
Derivatives(4)		$	—		$	—		$	367		$	367
-1	Included in cash and cash equivalents on our consolidated balance sheets.
-2	Included in current portion of marketable securities on our consolidated balance sheets.
-3	Included in noncurrent portion of marketable securities on our consolidated balance sheets.
-4	Included in fair value of derivatives on our consolidated balance sheets.
Changes in Level 3 Recurring Fair Value Measurements
The table below includes a rollforward of the balance sheet amounts for the year ended December 31, 2014, including the change in fair value, for financial instruments in the Level 3 category. When a determination is made to classify a financial instrument within Level 3, the determination is based upon the significance of the unobservable parameters to the overall fair value measurement. However, Level 3 financial instruments typically include, in addition to the unobservable components, observable components (that is, components that are actively quoted and can be validated to external sources). Accordingly, the gain in the table below includes changes in fair value due in part to observable factors that are part of the methodology.
		Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Year Ended December 31, 2014
(In thousands)		Fair Value at			Total			Purchases,			Transfers			Fair Value at			Change in
		December 31,			Unrealized			Sales,			In and/or			December 31,			Unrealized Gain
		2013			Gain			Issuances,			Out of			2014			Related to
					Included in			Settlements			Level 3						Financial
					Earnings(1)												Instruments
																	Held at
																	December 31,
																	2014(1)
Derivative liabilities		$	367		$	(351	)	$	—		$	—		$	16		$	(351	)
-1	Reported as unrealized gain on derivatives in our consolidated statements of operations.
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, 2014
PROPERTY AND EQUIPMENT
PROPERTY AND EQUIPMENT
	3. PROPERTY AND EQUIPMENT
	Property and equipment, stated at cost, is comprised of the following:
		December 31,
	(In thousands)	2014			2013
	Furniture and computer equipment	$	1,158		$	1,092
	Lab equipment		130			118
	Leasehold improvements		74			74
			1,362			1,284
	Less accumulated depreciation and amortization		(1,189	)		(1,192	)
		$	173		$	92

EQUIPMENT_LINE

EQUIPMENT LINE	12 Months Ended
	Dec. 31, 2014
EQUIPMENT LINE
EQUIPMENT LINE
	4. EQUIPMENT LINE
	In 2009, we renewed our equipment financing facility and had approximately $500,000 available for borrowing. This facility was secured by a certificate of deposit. In 2014, we closed the certificate of deposit for our unused equipment line of credit upon maturity and transferred the cash proceeds to our cash operating accounts. This action also cancelled the availability of the equipment line of credit. We had no amounts due under this facility as of December 31, 2013.

ACCRUED_LIABILITIES

ACCRUED LIABILITIES	12 Months Ended
	Dec. 31, 2014
ACCRUED LIABILITIES
ACCRUED LIABILITIES
	5. ACCRUED LIABILITIES
	Accrued liabilities consisted of the following:
		December 31,
	(In thousands)	2014		2013
	Service provider obligations	$	408	$	840
	Clinical trial costs		513		326
	Other		616		617
		$	1,537	$	1,783

RESTRUCTURING

RESTRUCTURING	12 Months Ended
	Dec. 31, 2014
RESTRUCTURINGS
RESTRUCTURINGS
	6. RESTRUCTURINGS
	April 2013 Restructuring
	On April 25, 2013, we announced the decision to discontinue our discovery research programs and companion diagnostics program based on telomere length and close our research laboratory facility located at 200 Constitution Drive, Menlo Park, California. With this decision, a total of 20 positions were eliminated. In connection with this restructuring, we incurred aggregate restructuring charges of $1,370,000 for the year ended December 31, 2013, of which $624,000 related to one-time termination benefits, including $28,000 of non-cash stock-based compensation expense relating to the extension of the post-termination exercise period through the end of December 2013 for certain stock options previously granted to terminated employees, $200,000 related to non-cash charges for write-downs of excess equipment and leasehold improvements and $546,000 related to costs associated with the closure of our research laboratory facility. In connection with the decision to close our research laboratory facility, we entered into an amendment to the lease agreement for the 200 Constitution Drive facility under which the lease terminated effective December 31, 2013. As consideration for the early termination of the lease, we paid the landlord the remaining rents due under the original term of the lease as well as certain facility maintenance costs, all of which have been included in restructuring charges. The restructuring resulted in aggregate cash expenditures of $1,085,000 after adjustments and non-cash credits. In 2013, we received proceeds of $1,080,000 from the sale of excess laboratory equipment in connection with the closure of our research laboratory facility. All actions associated with this restructuring were completed in 2013, and we do not anticipate incurring any further charges in connection with this restructuring.
	The components of the accrued restructuring charges included on our consolidated balance sheet relating to the April 2013 restructuring are summarized in the following table. As of December 31, 2014, we had no remaining obligations related to the April 2013 restructuring:
	(In thousands)	Employee			Facility			Total
		Severance and			Related
		Other Benefits			Charges
	Beginning accrual balance as of December 31, 2013	$	21		$	73		$	94
	Cash payments		(19	)		(73	)		(92	)
	Adjustments or non-cash credits		(2	)		—			(2	)
	Ending accrual balance as of December 31, 2014	$	—		$	—		$	—
	December 2012 Restructuring
	On December 3, 2012, we announced the decision to discontinue development of GRN1005. With this decision, a total of 43 positions were eliminated. In connection with this restructuring, we incurred aggregate restructuring charges of $2,794,000, of which $2,702,000 was recognized for the year ended December 31, 2012 and $92,000 was recognized for the year ended December 31, 2013. The aggregate restructuring charges consisted of $2,523,000 related to one-time termination benefits, including $107,000 of non-cash stock-based compensation expense relating to the extension of the post-termination exercise period through the end of December 2013 for certain stock options previously granted to terminated employees, and $271,000 related to non-cash charges for write-downs of GRN1005 manufacturing equipment. The restructuring resulted in aggregate cash expenditures of $2,271,000 after adjustments and non-cash credits. All actions associated with this restructuring were completed in 2013, and we do not anticipate incurring any further charges in connection with this restructuring.
	See Note 15 on Subsequent Event for discussion of an organizational resizing announced in March 2015.

DIVESTITURE_OF_STEM_CELL_ASSET

DIVESTITURE OF STEM CELL ASSETS	12 Months Ended
	Dec. 31, 2014
DIVESTITURE OF STEM CELL ASSETS
DIVESTITURE OF STEM CELL ASSETS
	7. DIVESTITURE OF STEM CELL ASSETS
	On October 1, 2013, we closed the transaction to divest our human embryonic stem cell assets and our autologous cellular immunotherapy program pursuant to the terms of the previously disclosed asset contribution agreement, or the Contribution Agreement, that we entered into in January 2013 with BioTime, Inc., or BioTime, and BioTime's subsidiary, Asterias Biotherapeutics, Inc., or Asterias (formerly known as BioTime Acquisition Corporation).
	In accordance with the terms of the Contribution Agreement, on October 1, 2013 we received 6,537,779 shares of Asterias Series A common stock representing 21.4% of Asterias' outstanding common stock as a class as of that date. We are also entitled to receive royalties from Asterias on the sale of products that are commercialized, if any, in reliance upon the patents we contributed to Asterias. In accordance with our contractual obligations under the Contribution Agreement, we distributed all of the shares of Asterias Series A common stock we received from Asterias to our stockholders on a pro rata basis, other than with respect to fractional shares and shares that would otherwise have been distributed to Geron stockholders residing in certain excluded jurisdictions, which shares, as required by the Contribution Agreement, were sold with the net cash proceeds therefrom distributed ratably to the stockholders who would otherwise have been entitled to receive such shares. We refer to the distribution by us of the Asterias Series A common stock, or cash in lieu thereof, as the Series A Distribution. We completed the Series A Distribution to eligible stockholders on August 15, 2014. As of December 31, 2014, we had no remaining obligations with respect to the Series A Distribution.
	We accounted for the divestiture of the stem cell assets as a nonmonetary transaction since we transferred intangible assets in exchange for a non-controlling interest in Asterias. The stem cell assets we contributed consisted primarily of intellectual property and know-how and did not meet the definition of a business for accounting purposes. A business consists of three elements: (i) inputs, (ii) processes and (iii) outputs. To be considered a business, only inputs and processes are required, which together form an integrated set of activities used to create outputs. Since we did not contribute any processes, such as operational processes or an organized workforce with the skills and experience to provide the necessary processes capable of being applied to inputs to create outputs, we determined the stem cell assets only represented inputs and therefore were not considered an integrated set of activities. Due to the significant research and development necessary to realize the commercial potential of the stem cell assets, we expensed all research and development costs associated with the stem cell assets as incurred and therefore, there was no recorded amount, or carrying value, for the stem cell assets on our consolidated balance sheets. Since the divestiture of the stem cell assets represented the transfer of nonfinancial assets that do not meet the definition of a business in exchange for a non-controlling equity interest in Asterias, we accounted for the transaction using the carrying amount, or book value, of the assets surrendered with no gain or loss recognized on the exchange, consistent with our accounting policy for such transactions. Because the stem cell assets had a carrying amount of zero, we applied a carrying amount of zero to the Asterias Series A common stock received in the divestiture.
	We applied the equity method of accounting to our investment in Asterias Series A common stock during the period of ownership from October 1, 2013 through August 15, 2014. Since our investment in Asterias had an initial carrying amount of zero upon the closing of the transactions contemplated by the Contribution Agreement on October 1, 2013 and we had no commitments to provide financial support or obligations to perform services or other activities for Asterias, we suspended the equity method of accounting on October 1, 2013. In addition, since Asterias incurred net losses during our period of ownership, no additional value has been recognized for Asterias Series A common stock. Accordingly, the completion of the Series A Distribution had no impact on our consolidated financial statements.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2014
COMMITMENTS AND CONTINGENCIES.
COMMITMENTS AND CONTINGENCIES
	8. COMMITMENTS AND CONTINGENCIES
	Purported Securities and Derivative Lawsuits
	On March 14, 2014, a purported securities class action lawsuit was commenced in the United States District Court for the Northern District of California, or the California District Court, naming as defendants us and certain of our officers. The lawsuit alleges violations of the Securities Exchange Act of 1934 in connection with allegedly false and misleading statements made by us related to our Phase 2 trial of imetelstat in patients with ET or PV. The plaintiff alleges, among other things, that we failed to disclose facts related to the occurrence of persistent low-grade LFT abnormalities observed in our Phase 2 trial of imetelstat in ET or PV patients and the potential risk of chronic liver injury following long-term exposure to imetelstat. The plaintiff seeks damages and an award of reasonable costs and expenses, including attorneys' fees. On March 28, 2014, a second purported securities class action lawsuit was commenced in the California District Court, and on June 6, 2014, a third purported securities lawsuit, not styled as a class action, was commenced in the United States District Court for the Southern District of Mississippi, or the Mississippi District Court, naming as defendants us and certain of our officers. These lawsuits, which are based on the same factual background as the purported securities class action lawsuit that commenced on March 14, 2014, also allege violations of the Securities Exchange Act of 1934 and seek damages and an award of reasonable costs and expenses, including attorneys' fees. On June 30, 2014, the California District Court consolidated both of the purported class actions filed in the California District Court and appointed a lead plaintiff and lead counsel to represent the purported class. On July 21, 2014, the California District Court ordered the lead plaintiff to file its consolidated amended complaint, which was filed on September 19, 2014. On August 11, 2014, we filed a motion to transfer the purported securities lawsuit filed in the Mississippi District Court to the California District Court. On November 4, 2014, the Mississippi District Court granted our motion and transferred the case to the California District Court, which was thereafter consolidated with the class actions. On November 18, 2014, we filed a motion with the California District Court to dismiss the consolidated amended complaint. The plaintiff's opposition to our motion to dismiss was filed on January 20, 2015, and we filed our reply on February 25, 2015. The court hearing for the motion to dismiss has been scheduled for April 10, 2015. We believe that we have meritorious defenses and intend to defend against these lawsuits vigorously.
	On April 21, 2014, a stockholder purporting to act on our behalf filed a derivative lawsuit in the Superior Court of California for the County of San Mateo against certain of our officers and directors. The lawsuit alleges breaches of fiduciary duties by the defendants and other violations of law. In general, the lawsuit alleges that the defendants caused or allowed the dissemination of allegedly false and misleading statements related to our Phase 2 trial of imetelstat in patients with ET or PV. The plaintiff is seeking unspecified monetary damages and other relief, including reforms and improvements to our corporate governance and internal procedures. It is possible that additional derivative lawsuits will be filed with respect to these same or other matters and also naming our officers and directors as defendants. We have not yet responded to the derivative lawsuit, but intend to vigorously defend against the claims alleged and to seek dismissal of the lawsuit.
	For a further discussion of these ongoing lawsuits, refer to the section entitled "Legal Proceedings" in Part I, Item 3 of this annual report Form 10-K. These lawsuits and any other related lawsuits are subject to inherent uncertainties, and the actual defense and disposition costs will depend upon many unknown factors. The outcome of these lawsuits is necessarily uncertain. We could be forced to expend significant resources in the defense against these and any other related lawsuits and we may not prevail. We currently are not able to estimate the possible cost to us from these lawsuits, as they are currently at an early stage, and we cannot be certain how long it may take to resolve these lawsuits or the possible amount of any damages that we may be required to pay. Such amounts could be material to our consolidated financial statements even if we prevail in the defense against these lawsuits. We have not established any reserves for any potential liability relating to these lawsuits. It is possible that we could, in the future, incur judgments or enter into settlements of claims for monetary damages.
	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. We have no such obligations on our consolidated balance sheets as of December 31, 2014 and 2013.
	Operating Lease Commitment
	In February 2014, we amended the lease agreement for our premises at 149 Commonwealth Drive to extend the lease term through January 2016. As of December 31, 2014, future minimum payments under our operating lease for our premises at 149 Commonwealth Drive were approximately $959,000. Rent expense under our operating leases was approximately $936,000, $1,422,000 and $1,474,000 for the years ended December 31, 2014, 2013 and 2012, respectively.
	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 most significantly provides for, among other benefits: (i) a severance payment upon a Change of Control Triggering Event and Separation from Service (as defined in the Severance Plan) 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 is defined as an event 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. A Non-Change of Control Triggering Event 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, 2014, 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, 2014
STOCKHOLDERS' EQUITY
STOCKHOLDERS' EQUITY
	9. STOCKHOLDERS' EQUITY
	Public Offering
	On February 4, 2014, we completed an underwritten public offering of 25,875,000 shares of our common stock at a public offering price of $4.00 per share, resulting in net cash proceeds of approximately $96,805,000 after deducting the underwriting discount and offering expenses payable by us.
	Warrants
	As of December 31, 2014, the following warrants to purchase our common stock were outstanding and classified as equity:
	Issuance Date		Exercise			Number of			Exercisable		Expiration
			Price			Shares			Date		Date
	August 2011(1)		$	3.98			537,893		Aug-11		Aug-21
	Apr-05		$	3.75			470,000		Apr-05		Apr-15
							1,007,893
	-1	In connection with each disbursement under the loan agreement with 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. In December 2014, CIRM exercised a warrant to purchase 461,382 shares of our common stock utilizing the net exercise provision in the warrant resulting in the issuance of 168,039 shares of our common stock.
	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.
	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 to employees (including officers and employee directors) of either incentive stock 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, 2014, an aggregate of 13,384,883 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 originally granted under the 2002 Plan or 1996 Directors' Stock Option Plan, 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 100% of 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 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 2014, we have not repurchased any shares under the 2011 Plan. As of December 31, 2014, we have no shares outstanding subject to repurchase.
	Our Non-Employee Director Compensation Policy adopted by our board of directors in March 2014 provides for the automatic grant 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 70,000 shares of common stock on the date such person first becomes a non-employee director, or First Director Option. The First Director Option shall vest 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 35,000 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 one year from the date of grant.
	1996 Directors' Stock Option Plan
	The 1996 Directors' Stock Option Plan, or 1996 Directors Plan, expired in July 2006 upon which no further option grants were made from the 1996 Directors Plan. The options granted under the 1996 Directors Plan were nonstatutory stock options and 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. Options to purchase shares of common stock generally were 100% vested upon grant, except for options granted upon first appointment to the board of directors. These initial options vested annually over three years upon each anniversary date of appointment to the board of directors.
	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 grants made thereunder.
	The options granted 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 members of the board of 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 members of the board of 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, 1996 Directors Plan and 2006 Directors Plan is as follows:
						Outstanding Options
			Shares			Number of			Weighted Average			Weighted Average		Aggregate
			Available			Shares			Exercise Price			Remaining		Intrinsic
			For Grant						Per Share			Contractual Life		Value
												(In years)		(In thousands)
	Balance at December 31, 2013			16,207,250			15,576,216		$	3.04				$	33,798
	Options granted			(5,658,931	)		5,658,931		$	4.85
	Awards granted			(59,330	)		—		$	—
	Options exercised			—			(662,626	)	$	1.94
	Options cancelled/forfeited			3,613,577			(3,613,577	)	$	5.48
	Awards cancelled/forfeited			142,375			—		$	—
	2006 Directors Plan termination			(860,058	)		—		$	—
	Balance at December 31, 2014			13,384,883			16,958,944		$	3.16			7.38	$	16,038
	Options exercisable at December 31, 2014						9,129,576		$	3.12			6.47	$	9,231
	Options fully vested and expected to vest at December 31, 2014						16,225,022		$	3.14			7.32	$	15,546
	The aggregate intrinsic value in the preceding table represents the total intrinsic value, based on Geron's closing stock price of $3.25 per share as of December 31, 2014, which would have been received by the option holders had all the option holders exercised their options as of that date.
	There were no options granted with an exercise price below or greater than fair market value of our common stock on the date of grant in 2014, 2013 or 2012. As of December 31, 2014, 2013 and 2012, there were 9,129,576, 8,144,040 and 10,410,194 exercisable options outstanding at weighted average exercise prices per share of $3.12, $4.26 and $5.49, respectively.
	The total pretax intrinsic value of stock options exercised during 2014, 2013 and 2012 was $989,000, $2,787,000 and $100, respectively. Cash received from the exercise of options in 2014, 2013 and 2012 totaled approximately $1,286,000, $6,567,000 and $1,000, respectively. No income tax benefit was realized from stock options exercised in 2014 since we reported an operating loss.
	Information about stock options outstanding as of December 31, 2014 is as follows:
			Options Outstanding
	Exercise Price Range		Number of			Weighted Average			Weighted Average
			Shares			Exercise Price			Remaining
						Per Share			Contractual Life
									(In years)
	$1.10 - $1.50			4,284,937		$	1.42			7.41
	$1.51 - $2.14			4,278,382		$	1.64			7.84
	$2.16 - $5.01			5,376,639		$	4.29			7.91
	$5.05 - $9.32			3,018,986		$	5.80			5.72
	$1.10 - $9.32			16,958,944		$	3.16			7.38
	Aggregate restricted stock activity for the 2002 Plan, 2011 Plan and 2006 Directors Plan is as follows:
			Number of			Weighted			Weighted Average
			Shares			Average			Remaining
						Grant Date			Contractual Term
						Fair Value			(In years)
						Per Share
	Non-vested restricted stock at December 31, 2013			409,437		$	4.84			0.82
Granted			59,330		$	2.67
Vested			(265,422	)	$	4.47
Cancelled/forfeited			(142,375	)	$	4.66
Non-vested restricted stock at December 31, 2014			60,970		$	4.73			0.37
The total fair value of restricted stock that vested during 2014, 2013 and 2012 was $782,000, $252,000 and $936,000, 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. However, outstanding purchase rights granted under the 1996 Purchase Plan prior to its termination remained subject to the terms of the 1996 Purchase Plan. A total of 968,829 shares of our common stock were issued under the 1996 Purchase Plan since its adoption in July 1996 and reserves of 231,171 shares of our common stock for future issuance under the 1996 Purchase Plan were cancelled as of the date of termination and became available for future issuance for other corporate purposes. 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, 2014, 24,375 shares of our common stock have been issued under the 2014 Purchase Plan since its adoption.
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 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 only participate 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.
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's common stock on the employee's entry date into that offering period or (ii) the fair market value per share of Geron's common stock on the purchase date. If the fair market value of Geron's 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.
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 grant service-based stock options and restricted stock awards under our equity plans to employees, directors and consultants. The vesting period for employee options is generally four years. 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.
In the past, our board of directors has awarded to our employees and directors performance-based restricted stock awards and market-based restricted stock awards. We have not recognized any stock-based compensation expense for performance-based restricted stock awards in our consolidated statements of operations for the years ended December 31, 2014, 2013 and 2012 as the achievement of the specified performance criteria was not considered probable during that time. All of these awards have been cancelled unvested as the performance conditions were not achieved within the respective performance periods. The fair value for market-based restricted stock awards was determined using a lattice valuation model with a Monte Carlo simulation. All previously granted market-based restricted stock awards have been cancelled unvested as the market conditions were not achieved within the specified performance period.
As stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2014, 2013 and 2012 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.
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, 2014, 2013 and 2012 which was allocated as follows:
		Year Ended December 31,
(In thousands)		2014			2013			2012
Research and development		$	2,545		$	1,741		$	2,336
Restructuring charges			—			28			107
General and administrative			5,113			2,666			2,868
Stock-based compensation expense included in operating expenses		$	7,658		$	4,435		$	5,311
Modifications to the post-termination exercise period of outstanding options held by certain members of our executive management team resulted in additional stock-based compensation expense of $205,000 for the year ended December 31, 2013 and have been reflected in the above table. In addition, stock-based compensation expense has been recognized for the modification of the post-termination exercise period for certain stock options previously granted to employees affected by the April 2013 and December 2012 restructurings, which has been included in restructuring charges in our consolidated statements of operations. See Note 6 on Restructurings for further discussion of the restructurings.
The fair value of stock options granted in 2014, 2013 and 2012 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:
		2014		2013		2012
Dividend yield		0%		0%		0%
Expected volatility range		0.898 to 0.922		0.742 to 0.792		0.631 to 0.740
Risk-free interest rate range		1.64% to 1.92%		0.80% to 1.97%		0.81% to 1.25%
Expected term		5.5 yrs		6 yrs		6 yrs
The fair value of employee stock purchases in 2014, 2013 and 2012 under the 2014 Purchase Plan and 1996 Purchase Plan has been estimated using the Black Scholes option-pricing model with the following assumptions:
		2014		2013		2012
Dividend yield		0%		0%		0%
Expected volatility range		0.835 to 1.666		0.506 to 1.391		0.458 to 0.774
Risk-free interest rate range		0.06% to 0.15%		0.09% to 0.21%		0.06% to 0.21%
Expected term range		6 mos to 12 mos		6 mos to 12 mos		6 mos to 12 mos
Dividend yield is based on historical cash dividend payments and Geron has paid no dividends to date. The expected volatility range 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 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 employee stock options granted during the years ended December 31, 2014, 2013 and 2012 was $3.57, $1.03 and $0.89 per share, respectively. The weighted average estimated fair value of employees' purchase rights for the years ended December 31, 2014, 2013 and 2012 was $2.10, $0.75 and $0.59 per share, respectively. As of December 31, 2014, total compensation cost related to unvested share-based payment awards not yet recognized, net of estimated forfeitures, was $15,032,000, which is expected to be recognized over the next 27 months on a weighted-average basis.
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. We granted stock options to purchase 75,000, 80,000 and 50,000 shares of our common stock to consultants in 2014, 2013 and 2012, respectively. 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 $94,000, $92,000 and $135,000 for the vested portion of the fair value of stock options and restricted stock awards held by consultants in 2014, 2013 and 2012, respectively.
We have also issued common stock to consultants and vendors in exchange for services either performed or to be performed for us. For these stock issuances, 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 or goods are received. In 2014, 2013 and 2012, we issued 71,239, 66,853 and 170,298 shares of common stock, respectively, in exchange for goods or services. In 2014, 2013 and 2012, we recognized approximately $158,000, $202,000 and $1,010,000, respectively, of expense in connection with stock grants to consultants and vendors. As of December 31, 2014, $7,000 related to consultant and vendor stock issuances remained as a prepaid asset which is being amortized to our operating expenses on a pro-rata basis as services are incurred or goods are received.
Common Stock Reserved for Future Issuance
Common stock reserved for future issuance as of December 31, 2014 is as follows:
Outstanding stock options			16,958,944
Options and awards available for grant			13,384,883
Employee stock purchase plan			975,625
Warrants outstanding			1,007,893
Total			32,327,345
401(k) Plan
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. The Geron 401K Plan is intended to qualify under Section 401 of the Internal Revenue Code so that contributions by employees or by us, and income earned on the contributions, are not taxable to employees until withdrawn from the Geron 401K Plan. Our contributions, if any, will be deductible by us when made.
In 2014, our board of directors approved a cash matching contribution equal to 50% of each employee's contributions, which was fully vested when paid. We provided the 2014 matching contribution in February 2015. In 2013 and 2012, our board of directors approved a matching contribution equal to 75% and 100% of each employee's contributions, respectively. Those matching contributions were made in our common stock and vest ratably over four years for each year of service completed by the employee, commencing from the date of hire, until they are fully vested when the employee has completed four years of service.
For the vested portion of the 2014 match, we recorded $175,000 as research and development expense and $143,000 as general and administrative expense. For the vested portion of the 2013 match, we recorded $156,000 as research and development expense and $157,000 as general and administrative expense. For the vested portion of the 2012 match, we recorded $616,000 as research and development expense and $259,000 as general and administrative expense. Due to the number of positions eliminated in the previous restructurings, a partial plan termination was triggered in both 2013 and 2012. We accelerated the vesting of unvested prior employer matches for employees affected by the respective restructurings, which resulted in $266,000 and $370,000 of operating expenses in 2013 and 2012, respectively. As of December 31, 2014, approximately $273,000 remained unvested for the 2013, 2012 and 2011 matches which will be amortized to operating expenses as the corresponding years of service are completed by the employees.
Sales Agreement
On October 8, 2012, we entered into an At-the-Market Issuance Sales Agreement, or 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 sales agreement. Pursuant to the 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 sales agreement. As of December 31, 2014, we had not sold any common stock pursuant to the sales agreement. The sales agreement will expire in October 2015 unless extended by the parties.

LICENSE_AGREEMENTS

LICENSE AGREEMENTS	12 Months Ended
	Dec. 31, 2014
LICENSE AGREEMENTS
LICENSE AGREEMENTS
	10. LICENSE AGREEMENTS
	Janssen Biotech, Inc.
	In November 2014, we and Janssen Biotech, Inc., or Janssen, entered into an exclusive collaboration and license agreement, or Collaboration Agreement, to develop and commercialize imetelstat worldwide for oncology, including hematologic myeloid malignancies, and all other human therapeutic uses. Upon the early termination of the waiting periods under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, the Collaboration Agreement became effective on December 15, 2014. Upon the effectiveness of the Collaboration Agreement, we received $35,000,000 from Janssen as an upfront payment.
	Under the Collaboration Agreement, we granted to Janssen exclusive worldwide rights to develop and commercialize imetelstat for all indications, and Janssen is responsible for the development, manufacturing and commercialization of, and seeking regulatory approval for, imetelstat worldwide. Under the Collaboration Agreement, development of imetelstat will initially proceed under a mutually agreed joint clinical development plan, or CDP, which includes two agreed upon Phase 2 studies to be pursued initially, one in myelofibrosis, or the Initial Phase 2 MF Study, and one in myelodysplastic syndrome, or the Initial Phase 2 MDS Study, as well as additional, possible registration studies in myelofibrosis, or MF, and myelodysplastic syndrome, or MDS, and possible exploratory Phase 2 and potential follow-on Phase 3 studies in acute myelogenous leukemia, or AML. Development costs for the Initial Phase 2 MF Study and the Initial Phase 2 MDS Study will be shared between the parties on a 50/50 basis. We expect Janssen to initiate the Initial Phase 2 MF Study in mid-2015, followed later by the Initial Phase 2 MDS Study to be initiated at the end of 2015.
	Following the protocol-specified primary analysis of the Initial Phase 2 MF Study or after a certain time period after the initiation of the first Phase 3 MF study, Janssen must notify us whether it elects to maintain its license rights and continue to advance the development of imetelstat in any indication. In the event that the Initial Phase 2 MF Study has been terminated early or suspended, Janssen must instead notify us of its election by the date that is the later of 24 months from the initiation of the planned Initial Phase 2 MDS Study or 24 months from the termination of the planned Initial Phase 2 MF Study or commencement of the suspension period, as applicable.
	In the event that Janssen elects to continue to maintain its license rights and advance the development of imetelstat in any indication within the applicable timeframe set forth in the Collaboration Agreement (such election, the Continuation Election), we then would have an option, or the U.S. Opt-In Rights, to share further U.S. development and promotion costs in exchange for higher tiered royalty rates and higher future milestone payments if imetelstat is successfully developed and approved. If we exercise our U.S. Opt-In Rights, then the parties would share U.S. development and promotion costs on a 20/80 basis (Geron 20%, Janssen 80%), we would receive a $65,000,000 milestone payment, or Continuation Fee, at the time of the Continuation Election, and would be eligible to receive additional potential payments of up to $470,000,000 in development and regulatory milestones, up to $350,000,000 in 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 our U.S. Opt-In Rights, we then would also have a separate option, or the Co-Promotion Option, to provide 20% of the U.S. selling effort with 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 our Co-Promotion Option. We would be responsible for all costs associated with establishing and maintaining a sales force in any conduct of such co-promotion. All product sales would be booked by Janssen. If we do not exercise our U.S. Opt-In Rights, then all further development and promotion costs beyond the Initial Phase 2 MF Study or Initial Phase 2 MDS Study would be borne by Janssen, we would receive the $65,000,000 Continuation Fee at the time of the Continuation Election plus a $70,000,000 payment, or 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 in development and regulatory milestones, up to $350,000,000 in 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 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. For intellectual property developed under the Collaboration Agreement, or Development IP, the party having sole ownership interest in such Development IP would be responsible for prosecuting the patents, with Janssen bearing all of the costs for Development IP solely owned by Janssen and costs shared between the parties on a 50/50 basis for Development IP either jointly owned or solely owned by us.
	Under the terms of the Collaboration Agreement, we and Janssen 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 CDP and promotional activities (assuming we exercises our U.S. Opt-In Rights) for imetelstat, with Janssen responsible for the operational implementation of those activities. In addition, either of the parties may propose to the joint development committee imetelstat development for any new indications not then provided for in the joint CDP and if the parties agree such development should be conducted outside of the joint CDP, each of Geron and Janssen would be entitled to independently undertake such development at its own cost, subject to the other party's obligation to provide reimbursement for its specified portion of the costs plus a premium for such independent development 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 our U.S. Opt-In Rights following Janssen's Continuation Election, 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 a Continuation Election 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 a Continuation Election, then the Collaboration Agreement would terminate and all rights would revert to us. Janssen may terminate the Collaboration Agreement at any time for convenience and 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 would revert to us.
	The terms of the Janssen Collaboration Agreement contain multiple deliverables, which include 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 steering committees and working groups and (iv) potential participation in selling 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 steering committees, we determined our participation on the joint steering committees does not represent a non-contingent deliverable under the Collaboration Agreement. In addition, we determined our potential participation in selling imetelstat in the United States does not represent a non-contingent deliverable because such participation is uncertain and dependent on the drug being approved for commercial sale, which is not within our control. Accordingly, we have determined delivery of the license rights granted by us to Janssen, together with our performance of the technology transfer-related activities, represents the sole non-contingent deliverable under the Collaboration Agreement. Therefore, we will account for our delivery of the license rights and our performance of the technology transfer-related activities as a single unit of accounting. We currently expect completion of the technology transfer-related activities to occur by September 30, 2015 at which point we expect to fully recognize the $35,000,000 upfront payment from Janssen as license fee revenue. As a result, we have not recognized any revenue related to the Collaboration Agreement in 2014. 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 the Continuation Election, (ii) the Full U.S. Rights Fee if we do not exercise our U.S. Opt-In Rights and (iii) payments based on the achievement of certain development, regulatory or commercial milestones, represent substantive milestones. 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.
	The cost-sharing arrangement with Janssen for the Initial Phase 2 MF Study and the Initial Phase 2 MDS Study began in 2015. Therefore, we have not recorded any payables to Janssen or receivables from Janssen in 2014.
	GE Healthcare UK Limited
	In June 2009, we entered into a worldwide exclusive license and alliance agreement with GE Healthcare UK, Limited, or GEHC, to develop and commercialize cellular assay products derived from human embryonic stem cells, or hESCs, for use in drug discovery, development and toxicity screening. In connection with the GEHC agreement, we recognized $825,000 as license fee revenue in our consolidated statements of operations for the year ended December 31, 2012 which reflects the full recognition of a license payment from GEHC related to the exercise of an option to expand the scope of their original 2009 license agreement to include exclusive global rights to our intellectual property and know-how for the development and sale of cellular assays derived from induced pluripotent stem cells. Upon the closing of the divestiture of our stem cell assets on October 1, 2013, the GEHC agreement, including any future revenue payments thereunder, was transferred to Asterias. No license fee revenue was recognized under the GEHC agreement in 2013. For a further discussion of the divestiture of our stem cell assets, see Note 7 on Divestiture of Stem Cell Assets.
	Telomerase Activation Sciences, Inc.
	In December 2012, we entered into a Termination and Assignment Agreement, or the Assignment Agreement, with Asia Biotech Corporation, or Asia Biotech, and Telomerase Activation Sciences, Inc., or TA Sciences, pursuant to which we agreed to assign to TA Sciences the intellectual property, including patents previously licensed to Asia Biotech, related to our telomerase activation technology. As consideration for the assignment and fulfillment of the obligations set forth in the Assignment Agreement, we received a non-refundable, upfront payment of $2,500,000 from TA Sciences, which we recognized in full as other income in our consolidated statements of operations for the year ended December 31, 2012, and TA Sciences does not have further payment obligations to us. In addition, Asia Biotech's future royalty obligations under the original license agreement have been terminated.

INCOME_TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2014
INCOME TAXES
INCOME TAXES
	11. 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,
		2014			2013
		(In thousands)
	Net operating loss carryforwards	$	281,300		$	271,800
	Purchased technology		—			6,300
	Research credits		23,400			22,700
	Capitalized research and development		2,100			6,600
	License fees		500			700
	Other—net		7,600			10,100
	Total deferred tax assets		314,900			318,200
	Valuation allowance for deferred tax assets		(314,900	)		(318,200	)
	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 $3,300,000 and $5,500,000 during the years ended December 31, 2014 and 2013, respectively, and increased by $14,200,000 during the year ended December 31, 2012. Approximately $4,900,000 of the valuation allowance for deferred tax assets relates to benefits of stock option deductions which, when recognized, will be allocated directly to contributed capital.
	As of December 31, 2014, we had domestic federal net operating loss carryforwards of approximately $774,000,000 expiring at various dates beginning in 2018 through 2034, and state net operating loss carryforwards of approximately $395,000,000 expiring at various dates beginning in 2015 through 2034, if not utilized. We also had federal research and development tax credit carryforwards of approximately $14,900,000 expiring at various dates beginning in 2018 through 2034, if not utilized. Our state research and development tax credit carryforwards of approximately $13,000,000 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.
	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, 2014, we had approximately $17,100,000 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, 2013	$	11,600
	Increase related to prior year tax positions		5,100
	Increase related to current year tax positions		400
	Settlements		—
	Reductions due to lapse of applicable statute of limitations		—
	Balance as of December 31, 2014	$	17,100
	If applicable, we would classify interest and penalties related to uncertain tax positions in income tax expense. Through December 31, 2014, 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, 2015. 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.

SEGMENT_INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2014
SEGMENT INFORMATION
SEGMENT INFORMATION
	12. SEGMENT INFORMATION
	Our executive management team represents our chief decision maker. We view our operations as one segment, the discovery and 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.

CONSOLIDATED_STATEMENTS_OF_CAS1

CONSOLIDATED STATEMENTS OF CASH FLOW DATA	12 Months Ended
	Dec. 31, 2014
CONSOLIDATED STATEMENTS OF CASH FLOW DATA
CONSOLIDATED STATEMENTS OF CASH FLOW DATA
	13. CONSOLIDATED STATEMENTS OF CASH FLOWS DATA
		Year Ended December 31,
		2014			2013			2012
		(In thousands)
	Supplemental operating activities:
	Issuance of common stock for services rendered to date or to be received in future periods	$	—		$	—		$	69
	Issuance of common stock for 401(k) matching contributions	$	313		$	839		$	1,361
	Reclassification between deposits and other current assets	$	190		$	219		$	526
	Supplemental investing activities:
	Net unrealized loss on marketable securities	$	(70	)	$	(54	)	$	(38	)
	We have not made any cash payments for taxes or interest for the years ended December 31, 2014, 2013 and 2012.

SELECTED_QUARTERLY_FINANCIAL_I

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)	12 Months Ended
	Dec. 31, 2014
SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
	14. SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
			First			Second			Third			Fourth
			Quarter			Quarter			Quarter			Quarter
			(In thousands, except per share amounts)
	Year Ended December 31, 2014
	Revenues		$	474		$	341		$	160		$	178
	Operating expenses			9,205			9,004			10,067			9,189
	Net loss			(8,440	)		(8,734	)		(9,549	)		(8,947	)
	Basic and diluted net loss per share		$	(0.06	)	$	(0.06	)	$	(0.06	)	$	(0.06	)
	Year Ended December 31, 2013
	Revenues		$	765		$	112		$	181		$	225
	Operating expenses(1)			12,750			9,077			8,914			9,500
	Net loss			(11,897	)		(8,947	)		(8,254	)		(9,281	)
	Basic and diluted net loss per share		$	(0.09	)	$	(0.07	)	$	(0.06	)	$	(0.07	)
	-1	The fourth quarter of 2013 includes approximately $430,000 in restructuring charges in connection with the closure our research laboratory facility located at 200 Constitution Drive, Menlo Park, California. See Note 6 on Restructurings.
	Basic and diluted net losses 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_EVENT

SUBSEQUENT EVENT	12 Months Ended
	Dec. 31, 2014
SUBSEQUENT EVENT
SUBSEQUENT EVENT
	15. SUBSEQUENT EVENT
	In light of 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 from 39 to 21 positions, representing a reduction of approximately 46% of our workforce. We expect the majority of the reduction in our workforce to be completed by the end of the third quarter of 2015. In connection with the resizing, we anticipate incurring aggregate restructuring charges of approximately $1,900,000, of which approximately $1,500,000 is expected be paid in cash during 2015. The aggregate projected restructuring charges represent one-time termination benefits, comprised principally of severance, benefit continuation costs, outplacement services and non-cash stock-based compensation expense associated with the elimination of 18 positions. The majority of these charges are expected to be recognized in the first half of 2015. We may incur other charges and will record these expenses in the appropriate period as they are determined.

ORGANIZATION_AND_SUMMARY_OF_SI1

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2014
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Principles of Consolidation
	Principles of Consolidation
	The consolidated financial statements include the accounts of Geron and our former wholly-owned subsidiary, Geron Bio-Med Ltd. (Geron Bio-Med), a United Kingdom company. In March 2012, the board of directors and shareholders of Geron Bio-Med approved actions to commence a voluntary winding up of the company. The full wind up of Geron Bio-Med was completed in August 2012. Prior to 2013, we eliminated intercompany accounts and transactions and prepared the financial statements of Geron Bio-Med using the local currency as the functional currency. We translated the assets and liabilities of Geron Bio-Med at rates of exchange at the balance sheet date and translated income and expense items at average monthly rates of exchange. The resultant translation adjustments were included in accumulated other comprehensive income (loss), a separate component of stockholders' equity.
Net Loss Per Share
	Net Loss Per Share
	Basic earnings (loss) per share is calculated based on the weighted average number of shares of common stock outstanding during the period. Diluted earnings (loss) per share is calculated based on the weighted average number of shares of common stock and potential dilutive securities outstanding during the period. Potential dilutive securities primarily consist of outstanding stock options, restricted stock awards and warrants to purchase common stock and are determined using the treasury stock method at an average market price during the period.
	Because we are in a net loss position, diluted loss per share excludes the effects of potential dilutive securities. Had we been in a net income position, diluted earnings per share would have included the shares used in the computation of basic net loss per share as well as an additional 3,072,340, 532,120 and 11,497 shares for 2014, 2013 and 2012, respectively, related to outstanding stock options, restricted stock awards and warrants (as determined using the treasury stock method at the estimated average market value).
Use of Estimates
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On a regular basis, management evaluates these estimates and assumptions. 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. Our marketable securities include U.S. government-sponsored enterprise securities, commercial paper and corporate notes with original maturities ranging from four to 19 months.
	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 consolidated 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 associated with credit losses judged as other-than-temporary result in a charge to interest and other income. Other-than-temporary charges not related to credit losses are included in accumulated other comprehensive income (loss) in stockholders' equity. We have not recorded any other-than-temporary impairment charges for our available-for-sale securities for the years ended December 31, 2014, 2013 and 2012. See Note 2 on Fair Value Measurements.
	Non-Marketable Equity Investments
	Non-marketable equity investments in companies in which we own less than 20% of the outstanding voting stock and do not otherwise have the ability to exert significant influence over the investees are carried at cost, as adjusted for other-than-temporary impairments. We apply the equity method of accounting for investments in non-marketable nonpublic companies in which we own more than 20% of the outstanding voting stock or otherwise have the ability to exert significant influence over the investees. Under this method, we increase (decrease) the carrying value of our investment by a proportionate share of the investee's earnings (losses). If losses exceed the carrying value of the investment, losses are then applied against any advances to the investee, including any commitment to provide financial support, until those amounts are reduced to zero. Commitments to provide financial support include formal guarantees, implicit arrangements, reputational expectations, intercompany relationships or a consistent past history of providing financial support. The equity method is then suspended until the investee has earnings. Any proportionate share of investee earnings is first applied to the share of accumulated losses not recognized during the period the equity method was suspended. We recognize previously suspended losses to the extent additional investment is determined to represent the funding of prior losses. See Note 7 on Divestiture of Stem Cell Assets.
	Fair Value of Derivatives
	For non-employee options classified as liabilities, the fair value of these instruments is recorded on the consolidated balance sheet at inception and adjusted to fair value at each financial reporting date. The change in fair value of the non-employee options is recorded in the consolidated statements of operations as unrealized gain (loss) on derivatives. Fair value of non-employee options is estimated using the Black Scholes option-pricing model. The non-employee options continue to be reported as a liability until such time as the instruments are exercised or expire or are otherwise modified to remove the provisions which require this treatment, at which time these instruments are marked to fair value and reclassified from liabilities to stockholders' equity. For non-employee options classified as permanent equity, the fair value of the non-employee options is recorded in stockholders' equity as of their respective vesting dates and no further adjustments are made. See Note 2 on Fair Value Measurements.
Nonmonetary Transactions
	Nonmonetary Transactions
	We account for nonmonetary transactions based on the fair values of the assets (or services) involved. The cost of a nonmonetary asset acquired in exchange for another nonmonetary asset is the fair value of the asset surrendered to obtain it with a gain or loss recognized on the exchange. We use the fair value of the asset received to measure the cost if it is more clearly evident than the fair value of the asset surrendered. If the fair value of neither the assets received nor the assets relinquished is determinable within reasonable limits, we use the recorded amount (or carrying value) of the nonmonetary assets relinquished to account for the exchange. Similarly, we use carrying value for an exchange of controlled assets that do not meet the definition of a business for a non-controlling non-marketable equity interest in a company with no gain or loss recognized on the exchange. See Note 7 on Divestiture of Stem Cell Assets.
Revenue Recognition
	Revenue Recognition
	In general, 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 with Janssen, 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 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: (1) the deliverables included in the arrangement and (2) 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 if (ii) 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 and the availability of the associated expertise in the general marketplace. In addition, we consider whether the collaboration partner 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, related to a license that has standalone value from the other deliverables to be provided under the agreement, have been delivered 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.
	At the inception of an arrangement that includes milestone payments, we assess whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the 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 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.
	Royalties are recognized as earned in accordance with contract terms when royalties from licensees can be reasonably estimated and collectability is reasonably assured. If royalties cannot be reasonably estimated or collectability of a royalty amount is not reasonably assured, royalties are recognized as revenue when the cash is received. Revenue from commercial milestone payments will be accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.
	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 depending 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 depending 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 separate certificate of deposit accounts for specified purposes. The components of restricted cash were as follows:
		December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases		266			265
		$	266		$	795
	In 2014, we closed the certificate of deposit for our unused equipment line of credit upon maturity and transferred the cash proceeds to our cash operating accounts. This action also cancelled the availability of the equipment line of credit.
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 and research-related overhead. Research and development costs are expensed as incurred, including payments made under our license agreements.
	Clinical Trial Costs
	A significant component of our research and development expenses has historically been clinical trial costs. Substantial portions of our preclinical studies and all of our clinical trials have been performed by third-party contract research organizations, or CROs, and other vendors. We accrue expenses for preclinical studies performed by our vendors based on certain estimates over the term of the service period and adjust our estimates as required. We accrue expenses for clinical trial activities performed by CROs based upon the estimated amount of work completed on each study. For clinical trial expenses, the significant factors used in estimating accruals include the number of patients enrolled, the number of active clinical sites and the duration for which the patients will be enrolled in the study. Pass through costs from CROs include, but are not limited to, regulatory expenses, investigator fees, lab fees, travel costs and other miscellaneous costs, including shipping and printing fees. We accrue pass through costs based on estimates of the amount of work completed for the clinical trial. We monitor patient enrollment levels and related activities to the extent possible through internal reviews, review of contractual terms and correspondence with CROs. We 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 on a straight-line basis over the requisite service period, which is generally the vesting period. For additional information, see Note 9 on Stockholders' Equity.
	Stock Options and Employee Stock Purchase Plan
	We grant service-based stock options under our equity plans to employees, directors and consultants. The vesting period for employee options is generally four years. We use the Black Scholes option-pricing model to estimate the grant-date fair value of our stock options and employee stock plan purchases. The determination of fair value for these stock-based awards on the date of grant 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. For additional information, see Note 9 on Stockholders' Equity.
	Restricted Stock Awards
	We have granted restricted stock awards to employees and directors with three types of vesting schedules: (i) service-based, (ii) performance-based or (iii) market-based. Service-based restricted stock awards generally vest annually over four years. Performance-based restricted stock awards vest upon achievement of discrete strategic corporate goals within a specified performance period, generally three years. Market-based restricted stock awards vest only upon achievement of certain market price thresholds of our common stock within a specified performance period, generally three years.
	The fair value for service-based restricted stock awards is determined using the fair value of our common stock on the date of grant. The fair value is amortized as stock-based compensation expense over the requisite service period of the award, which is generally the vesting period, on a straight-line basis and is reduced for estimated forfeitures, as applicable.
	The fair value for performance-based restricted stock awards is determined using the fair value of our common stock on the date of grant. Stock-based compensation expense for awards with vesting based on performance conditions is recognized over the period from the date the performance condition is determined to be probable of occurring through the date the applicable condition is expected to be met and is reduced for estimated forfeitures, as applicable. If the performance condition is not considered probable of being achieved, no stock-based compensation expense is recognized until such time as the performance condition is considered probable of being met, if at all. If that assessment of the probability of the performance condition being met changes, the impact of the change in estimate would be recognized in the period of the change. If the requisite service period has been met prior to the change in estimate, the effect of the change in estimate would be recognized immediately. All previously granted performance-based restricted stock awards have been cancelled unvested as the performance conditions were not achieved within the respective performance periods.
	The fair value for market-based restricted stock awards is determined using a lattice valuation model with a Monte Carlo simulation. The model takes into consideration the historical volatility of our stock and the risk-free interest rate at the date of grant. In addition, the model is used to estimate the derived service period for the awards. The derived service period is the estimated period of time that would be required to satisfy the market condition, assuming the market condition will be satisfied. Stock-based compensation expense is recognized over the derived service period for the awards using the straight-line method and is reduced for estimated forfeitures, as applicable, but is accelerated if the market condition is achieved earlier than estimated. If a market-based restricted stock award is forfeited or expires after completion of the derived service period, any previously recognized stock-based compensation expense is not reversed. All previously granted market-based restricted stock awards have been cancelled unvested as the market conditions were not achieved within the specified performance 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 awards in our consolidated statements of operations.
Accumulated Other Comprehensive Loss
	Accumulated Other Comprehensive Loss
	Accumulated other comprehensive loss includes certain changes in stockholders' equity which are excluded from net loss. The components of accumulated other comprehensive loss were as follows:
		December 31,
	(In thousands)	2014			2013
	Unrealized loss on marketable securities	$	(84	)	$	(14	)
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 within operations would be recorded as income tax expense.
Concentrations of Customers and Suppliers
	Concentrations of Customers and Suppliers
	The majority of our revenues was earned in the United States. Two customers accounted for approximately 31%, 42% and 59% of our 2014, 2013 and 2012 revenues, respectively.
	We contract third-party manufacturers to produce GMP-grade drugs for preclinical and clinical studies. We also contract for starting materials to supply those manufacturers and us. Certain development and clinical activities may be delayed if we or Janssen are unable to obtain sufficient quantities of starting materials or GMP-grade drugs from current third-party suppliers or other third-party sources.
Recent Accounting Pronouncements
	Recent Accounting Pronouncements
	In April 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update No. 2014-08, Presentation of Financial Statements and Property, Plant, and Equipment: Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 raised the threshold for a disposal of assets to qualify as a discontinued operation and requires new disclosures for both discontinued operations and disposals of individually significant components of a business that do not qualify as discontinued operations. Under the new guidance, only disposals of assets representing a strategic shift in operations that has a major effect on the entity's operations and financial results should be presented as discontinued operations. If the disposal does qualify as a discontinued operation, the entity will be required to provide expanded disclosures, as well as disclosure of the pretax income attributable to the disposal of a significant part of an entity that does not qualify as a discontinued operation. ASU 2014-08 is effective for us beginning January 1, 2015 and subsequent interim periods. We do not expect the adoption of ASU 2014-08 to have a material effect on our consolidated financial statements.
	In May 2014, the FASB issued Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers, or ASU 2014-09. ASU 2014-09 provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 will require an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This update creates a five-step model that requires entities to exercise judgment when considering the terms of the contract(s). The five-step model includes: (i) identifying the contract(s) with the customer, (ii) identifying the separate performance obligations in the contract, (iii) determining the transaction price, (iv) allocating the transaction price to the separate performance obligations, and (v) recognizing revenue when each performance obligation is satisfied. ASU 2014-09 also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 will be effective for us beginning January 1, 2017 and subsequent interim periods. We have the option to apply the provisions of ASU 2014-09 either retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of applying this accounting standard recognized at the date of initial application. Early adoption is not permitted. We are currently evaluating the transition method and the impact that the adoption of ASU 2014-09 will have on our consolidated financial statements and related disclosures.
	In August 2014, the FASB issued Accounting Standard Update No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern, or ASU 2014-15. ASU 2014-15 is intended to define management's responsibility to evaluate whether there is substantial doubt about an organization's ability to continue as a going concern and to provide related footnote disclosures. Substantial doubt about an entity's ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 provides guidance to an organization's management, with principles and definitions that are intended to reduce diversity in the timing and content of disclosures that are commonly provided by organizations in financial statement footnotes. ASU 2014-15 will be effective for us beginning December 31, 2016 and subsequent interim periods. Early adoption is permitted. We are currently in the process of evaluating the impact of adoption of ASU 2014-15 on our consolidated financial statements and related disclosures.

ORGANIZATION_AND_SUMMARY_OF_SI2

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2014
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Schedule of components of restricted cash
		December 31,
	(In thousands)	2014			2013
	Certificate of deposit for unused equipment line of credit	$	—		$	530
	Certificate of deposit for credit card purchases		266			265
		$	266		$	795
Schedule of components of accumulated other comprehensive loss
		December 31,
	(In thousands)	2014			2013
	Unrealized loss on marketable securities	$	(84	)	$	(14	)

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS
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, 2014 were as follows:
	(In thousands)		Amortized Cost			Gross Unrealized Gains			Gross Unrealized Losses			Estimated Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	40,342		$	—		$	—		$	40,342
	Restricted cash:
	Certificate of deposit		$	266		$	—		$	—		$	266
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	401		$	—		$	(1	)	$	400
	Government-sponsored enterprise securities (due in 1 to 2 years)			6,556			—			(7	)		6,549
	Commercial paper (due in less than 1 year)			10,985			14			—			10,999
	Corporate notes (due in less than 1 year)			97,307			2			(63	)		97,246
	Corporate notes (due in 1 to 2 years)			12,412			—			(29	)		12,383
			$	127,661		$	16		$	(100	)	$	127,577
	Cash equivalents, restricted cash and marketable securities by security type at December 31, 2013 were as follows:
	(In thousands)		Amortized Cost			Gross Unrealized Gains			Gross Unrealized Losses			Estimated Fair Value
	Included in cash and cash equivalents:
	Money market funds		$	8,079		$	—		$	—		$	8,079
	Corporate notes			2,206			—			—			2,206
			$	10,285		$	—		$	—		$	10,285
	Restricted cash:
	Certificates of deposit		$	795		$	—		$	—		$	795
	Marketable securities:
	Government-sponsored enterprise securities (due in less than 1 year)		$	7,369		$	1		$	(1	)	$	7,369
	Commercial paper (due in less than 1 year)			5,496			3			—			5,499
	Corporate notes (due in less than 1 year)			39,383			1			(18	)		39,366
			$	52,248		$	5		$	(19	)	$	52,234
Schedule of marketable securities with unrealized losses
			Less Than 12 Months						12 Months or Greater						Total
	(In thousands)		Estimated Fair Value			Gross Unrealized Losses			Estimated Fair Value			Gross Unrealized Losses			Estimated Fair Value			Gross Unrealized Losses
	As of December 31, 2014:
	Government-sponsored enterprise securities (due in less than 1 year)		$	400		$	(1	)	$	—		$	—		$	400		$	(1	)
	Government-sponsored enterprise securities (due in 1 to 2 years)			5,549			(7	)		—			—			5,549			(7	)
	Corporate notes (due in less than 1 year)			92,989			(63	)		—			—			92,989			(63	)
	Corporate notes (due in 1 to 2 years)			12,383			(29	)		—			—			12,383			(29	)
			$	111,321		$	(100	)	$	—		$	—		$	111,321		$	(100	)
	As of December 31, 2013:
	Government-sponsored enterprise securities (due in less than 1 year)		$	3,947		$	(1	)	$	—		$	—		$	3,947		$	(1	)
	Corporate notes (due in less than 1 year)			37,060			(18	)		—			—			37,060			(18	)
			$	41,007		$	(19	)	$	—		$	—		$	41,007		$	(19	)
Schedule of non-employee options to purchase common stock considered as derivatives and classified as current liabilities
						Number of Shares at December 31,										Fair Value at December 31,
			Exercise									Exercisable		Expiration
	Issuance Date		Price			2014			2013			Date		Date		2014			2013
																(In thousands)
	Mar-05		$	6.39			284,600			284,600		Jan-07		Mar-15		$	16		$	367
Schedule of assumptions used to estimate the fair value of derivatives
			December 31,
			2014		2013
	Dividend yield		0%		0%
	Expected volatility		0.895		0.844
	Risk-free interest rate		0.04%		0.13%
	Expected term		0.25 yr		1 yr
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, 2014 and indicates the fair value category assigned.
			Fair Value Measurements at Reporting Date Using
			Quoted Prices in			Significant			Significant
			Active Markets for			Other			Unobservable
			Identical Assets /			Observable			Inputs
			Liabilities			Inputs
	(In thousands)		Level 1			Level 2			Level 3			Total
	Assets
	Money market funds(1)		$	40,342		$	—		$	—		$	40,342
	Government-sponsored enterprise securities(2)(3)			—			6,949			—			6,949
	Commercial paper(2)			—			10,999			—			10,999
	Corporate notes(2)(3)			—			109,629			—			109,629
	Total		$	40,342		$	127,577		$	—		$	167,919
	Liabilities
	Derivatives(4)		$	—		$	—		$	16		$	16
	The following table presents information about our financial instruments that are measured at fair value on a recurring basis as of December 31, 2013 and indicates the fair value category assigned.
			Fair Value Measurements at Reporting Date Using
			Quoted Prices in			Significant			Significant
			Active Markets for			Other			Unobservable
			Identical Assets /			Observable			Inputs
			Liabilities			Inputs
	(In thousands)		Level 1			Level 2			Level 3			Total
	Assets
	Money market funds(1)		$	8,079		$	—		$	—		$	8,079
	Government-sponsored enterprise securities(2)			—			7,369			—			7,369
	Commercial paper(2)			—			5,499			—			5,499
	Corporate notes(1)(2)			—			41,572			—			41,572
	Total		$	8,079		$	54,440		$	—		$	62,519
	Liabilities
	Derivatives(4)		$	—		$	—		$	367		$	367
	-1	Included in cash and cash equivalents on our consolidated balance sheets.
	-2	Included in current portion of marketable securities on our consolidated balance sheets.
	-3	Included in noncurrent portion of marketable securities on our consolidated balance sheets.
	-4	Included in fair value of derivatives on our consolidated balance sheets.
Schedule of rollforward of the balance sheet amounts for financial instruments in Level 3 category
			Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
			Year Ended December 31, 2014
	(In thousands)		Fair Value at			Total			Purchases,			Transfers			Fair Value at			Change in
			December 31,			Unrealized			Sales,			In and/or			December 31,			Unrealized Gain
			2013			Gain			Issuances,			Out of			2014			Related to
						Included in			Settlements			Level 3						Financial
						Earnings(1)												Instruments
																		Held at
																		December 31,
																		2014(1)
	Derivative liabilities		$	367		$	(351	)	$	—		$	—		$	16		$	(351	)
	-1	Reported as unrealized gain on derivatives in our consolidated statements of operations.

PROPERTY_AND_EQUIPMENT_Tables

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2014
PROPERTY AND EQUIPMENT
Schedule of property and equipment, stated at cost		December 31,
	(In thousands)	2014			2013
	Furniture and computer equipment	$	1,158		$	1,092
	Lab equipment		130			118
	Leasehold improvements		74			74
			1,362			1,284
	Less accumulated depreciation and amortization		(1,189	)		(1,192	)
		$	173		$	92

ACCRUED_LIABILITIES_Tables

ACCRUED LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2014
ACCRUED LIABILITIES
Schedule of accrued liabilities
		December 31,
	(In thousands)	2014		2013
	Service provider obligations	$	408	$	840
	Clinical trial costs		513		326
	Other		616		617
		$	1,537	$	1,783

RESTRUCTURINGS_Tables

RESTRUCTURINGS (Tables)	12 Months Ended
	Dec. 31, 2014
RESTRUCTURINGS
Summary of components of restructuring liability
	(In thousands)	Employee			Facility			Total
		Severance and			Related
		Other Benefits			Charges
	Beginning accrual balance as of December 31, 2013	$	21		$	73		$	94
	Cash payments		(19	)		(73	)		(92	)
	Adjustments or non-cash credits		(2	)		—			(2	)
	Ending accrual balance as of December 31, 2014	$	—		$	—		$	—

STOCKHOLDERS_EQUITY_Tables

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2014
STOCKHOLDERS' EQUITY
Schedule of warrants outstanding to purchase common stock and classified as equity
	As of December 31, 2014, the following warrants to purchase our common stock were outstanding and classified as equity:
	Issuance Date		Exercise			Number of			Exercisable		Expiration
			Price			Shares			Date		Date
	August 2011(1)		$	3.98			537,893		Aug-11		Aug-21
	Apr-05		$	3.75			470,000		Apr-05		Apr-15
							1,007,893
	-1	In connection with each disbursement under the loan agreement with 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. In December 2014, CIRM exercised a warrant to purchase 461,382 shares of our common stock utilizing the net exercise provision in the warrant resulting in the issuance of 168,039 shares of our common stock.
Schedule of aggregate option and award activity
						Outstanding Options
			Shares			Number of			Weighted Average			Weighted Average		Aggregate
			Available			Shares			Exercise Price			Remaining		Intrinsic
			For Grant						Per Share			Contractual Life		Value
												(In years)		(In thousands)
	Balance at December 31, 2013			16,207,250			15,576,216		$	3.04				$	33,798
	Options granted			(5,658,931	)		5,658,931		$	4.85
	Awards granted			(59,330	)		—		$	—
	Options exercised			—			(662,626	)	$	1.94
	Options cancelled/forfeited			3,613,577			(3,613,577	)	$	5.48
	Awards cancelled/forfeited			142,375			—		$	—
	2006 Directors Plan termination			(860,058	)		—		$	—
	Balance at December 31, 2014			13,384,883			16,958,944		$	3.16			7.38	$	16,038
	Options exercisable at December 31, 2014						9,129,576		$	3.12			6.47	$	9,231
	Options fully vested and expected to vest at December 31, 2014						16,225,022		$	3.14			7.32	$	15,546
Schedule of information about stock options outstanding by exercise price range
	Information about stock options outstanding as of December 31, 2014 is as follows:
			Options Outstanding
	Exercise Price Range		Number of			Weighted Average			Weighted Average
			Shares			Exercise Price			Remaining
						Per Share			Contractual Life
									(In years)
	$1.10 - $1.50			4,284,937		$	1.42			7.41
	$1.51 - $2.14			4,278,382		$	1.64			7.84
	$2.16 - $5.01			5,376,639		$	4.29			7.91
	$5.05 - $9.32			3,018,986		$	5.80			5.72
	$1.10 - $9.32			16,958,944		$	3.16			7.38
Schedule of aggregate restricted stock activity
			Number of			Weighted			Weighted Average
			Shares			Average			Remaining
						Grant Date			Contractual Term
						Fair Value			(In years)
						Per Share
	Non-vested restricted stock at December 31, 2013			409,437		$	4.84			0.82
	Granted			59,330		$	2.67
	Vested			(265,422	)	$	4.47
	Cancelled/forfeited			(142,375	)	$	4.66
	Non-vested restricted stock at December 31, 2014			60,970		$	4.73			0.37
Summary of allocation of stock-based compensation expense related to share-based payment awards
			Year Ended December 31,
	(In thousands)		2014			2013			2012
	Research and development		$	2,545		$	1,741		$	2,336
	Restructuring charges			—			28			107
	General and administrative			5,113			2,666			2,868
	Stock-based compensation expense included in operating expenses		$	7,658		$	4,435		$	5,311
Schedule of assumptions used to estimate the fair value of stock options granted
			2014		2013		2012
	Dividend yield		0%		0%		0%
	Expected volatility range		0.898 to 0.922		0.742 to 0.792		0.631 to 0.740
	Risk-free interest rate range		1.64% to 1.92%		0.80% to 1.97%		0.81% to 1.25%
	Expected term		5.5 yrs		6 yrs		6 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the Purchase Plans
			2014		2013		2012
	Dividend yield		0%		0%		0%
	Expected volatility range		0.835 to 1.666		0.506 to 1.391		0.458 to 0.774
	Risk-free interest rate range		0.06% to 0.15%		0.09% to 0.21%		0.06% to 0.21%
	Expected term range		6 mos to 12 mos		6 mos to 12 mos		6 mos to 12 mos
Schedule of common stock reserved for future issuance
	Common stock reserved for future issuance as of December 31, 2014 is as follows:
	Outstanding stock options			16,958,944
	Options and awards available for grant			13,384,883
	Employee stock purchase plan			975,625
	Warrants outstanding			1,007,893
	Total			32,327,345

INCOME_TAXES_Tables

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2014
INCOME TAXES
Schedule of significant components of the entity's deferred tax assets
		December 31,
		2014			2013
		(In thousands)
	Net operating loss carryforwards	$	281,300		$	271,800
	Purchased technology		—			6,300
	Research credits		23,400			22,700
	Capitalized research and development		2,100			6,600
	License fees		500			700
	Other—net		7,600			10,100
	Total deferred tax assets		314,900			318,200
	Valuation allowance for deferred tax assets		(314,900	)		(318,200	)
	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, 2013	$	11,600
	Increase related to prior year tax positions		5,100
	Increase related to current year tax positions		400
	Settlements		—
	Reductions due to lapse of applicable statute of limitations		—
	Balance as of December 31, 2014	$	17,100

CONSOLIDATED_STATEMENTS_OF_CAS2

CONSOLIDATED STATEMENTS OF CASH FLOWS DATA (Tables)	12 Months Ended
	Dec. 31, 2014
CONSOLIDATED STATEMENTS OF CASH FLOW DATA
Supplemental schedule of non-cash operating and investing activities
		Year Ended December 31,
		2014			2013			2012
		(In thousands)
	Supplemental operating activities:
	Issuance of common stock for services rendered to date or to be received in future periods	$	—		$	—		$	69
	Issuance of common stock for 401(k) matching contributions	$	313		$	839		$	1,361
	Reclassification between deposits and other current assets	$	190		$	219		$	526
	Supplemental investing activities:
	Net unrealized loss on marketable securities	$	(70	)	$	(54	)	$	(38	)

SELECTED_QUARTERLY_FINANCIAL_I1

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2014
SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
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, 2014
	Revenues		$	474		$	341		$	160		$	178
	Operating expenses			9,205			9,004			10,067			9,189
	Net loss			(8,440	)		(8,734	)		(9,549	)		(8,947	)
	Basic and diluted net loss per share		$	(0.06	)	$	(0.06	)	$	(0.06	)	$	(0.06	)
	Year Ended December 31, 2013
	Revenues		$	765		$	112		$	181		$	225
	Operating expenses(1)			12,750			9,077			8,914			9,500
	Net loss			(11,897	)		(8,947	)		(8,254	)		(9,281	)
	Basic and diluted net loss per share		$	(0.09	)	$	(0.07	)	$	(0.06	)	$	(0.07	)
	-1	The fourth quarter of 2013 includes approximately $430,000 in restructuring charges in connection with the closure our research laboratory facility located at 200 Constitution Drive, Menlo Park, California. See Note 6 on Restructurings.

ORGANIZATION_AND_SUMMARY_OF_SI3

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Loss Per Share
Potential dilutive securities excluded from diluted earnings (loss) per share calculation (in shares)	3,072,340	532,120	11,497
Minimum
Marketable securities
Original maturity period of marketable securities	4 months
Maximum
Marketable securities
Original maturity period of marketable securities	19 months

ORGANIZATION_AND_SUMMARY_OF_SI4

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Restricted Cash
Carrying value of restricted cash	$266	$795
Depreciation and Amortization
Estimated useful lives of assets	4 years
Certificate of deposit for unused equipment line of credit
Restricted Cash
Carrying value of restricted cash		530
Certificate of deposit for credit card purchases
Restricted Cash
Carrying value of restricted cash	$266	$265

ORGANIZATION_AND_SUMMARY_OF_SI5

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3)	12 Months Ended
	Dec. 31, 2014
	item
Restricted stock awards
Stock-Based Compensation
Types of vesting schedules (in count)	3
Service-based restricted stock awards
Stock-Based Compensation
Vesting period of awards	4 years
Performance-based restricted stock awards
Stock-Based Compensation
Vesting period of awards	3 years
Market-based restricted stock awards
Stock-Based Compensation
Vesting period of awards	3 years
Stock options
Stock-Based Compensation
Vesting period of awards	4 years

ORGANIZATION_AND_SUMMARY_OF_SI6

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Loss
Unrealized loss on marketable securities	($84)	($14)

ORGANIZATION_AND_SUMMARY_OF_SI7

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 5) (Concentrations of Customers and Suppliers)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	item	item	item
Concentrations of Customers and Suppliers
Concentration risk
Number of customers	2	2	2
Concentration risk percentage	31.00%	42.00%	59.00%

FAIR_VALUE_MEASUREMENTS_Detail

FAIR VALUE MEASUREMENTS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Included in cash and cash equivalents
Amortized Cost	$40,342	$10,285
Estimated Fair Value	40,342	10,285
Restricted cash
Amortized Cost	266	795
Estimated Fair Value	266	795
Marketable securities
Amortized Cost	127,661	52,248
Gross Unrealized Gains	16	5
Gross Unrealized Losses	-100	-19
Estimated Fair Value	127,577	52,234
Money market funds
Included in cash and cash equivalents
Amortized Cost	40,342	8,079
Estimated Fair Value	40,342	8,079
Corporate notes
Included in cash and cash equivalents
Amortized Cost		2,206
Estimated Fair Value		2,206
Certificates of deposit
Restricted cash
Amortized Cost	266	795
Estimated Fair Value	266	795
Government-sponsored enterprise securities (due in less than 1 year)
Marketable securities
Amortized Cost	401	7,369
Gross Unrealized Gains		1
Gross Unrealized Losses	-1	-1
Estimated Fair Value	400	7,369
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities
Amortized Cost	6,556
Gross Unrealized Losses	-7
Estimated Fair Value	6,549
Commercial paper (due in less than 1 year)
Marketable securities
Amortized Cost	10,985	5,496
Gross Unrealized Gains	14	3
Estimated Fair Value	10,999	5,499
Corporate notes (due in less than 1 year)
Marketable securities
Amortized Cost	97,307	39,383
Gross Unrealized Gains	2	1
Gross Unrealized Losses	-63	-18
Estimated Fair Value	97,246	39,366
Corporate notes (due in 1 to 2 years)
Marketable securities
Amortized Cost	12,412
Gross Unrealized Losses	-29
Estimated Fair Value	$12,383

FAIR_VALUE_MEASUREMENTS_Detail1

FAIR VALUE MEASUREMENTS (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$111,321	$41,007
Less Than 12 Months - Gross Unrealized Losses	-100	-19
Total - Estimated Fair Value	111,321	41,007
Total - Gross Unrealized Losses	-100	-19
Government-sponsored enterprise securities (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	400	3,947
Less Than 12 Months - Gross Unrealized Losses	-1	-1
Total - Estimated Fair Value	400	3,947
Total - Gross Unrealized Losses	-1	-1
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	5,549
Less Than 12 Months - Gross Unrealized Losses	-7
Total - Estimated Fair Value	5,549
Total - Gross Unrealized Losses	-7
Corporate notes (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	92,989	37,060
Less Than 12 Months - Gross Unrealized Losses	-63	-18
Total - Estimated Fair Value	92,989	37,060
Total - Gross Unrealized Losses	-63	-18
Corporate notes (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	12,383
Less Than 12 Months - Gross Unrealized Losses	-29
Total - Estimated Fair Value	12,383
Total - Gross Unrealized Losses	($29)

FAIR_VALUE_MEASUREMENTS_Detail2

FAIR VALUE MEASUREMENTS (Details 3) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives
Exercise Price (in dollars per share)	$3.16	$3.04
Number of Shares	16,958,944	15,576,216
Fair Value	$16	$367
Dividend yield (as a percent)	0.00%	0.00%
Expected volatility (as a percent)	89.50%	84.40%
Risk-free interest rate (as a percent)	0.04%	0.13%
Expected term	3 months	1 year
Non-employee options
Derivatives
Exercise Price (in dollars per share)	$6.39
Number of Shares	284,600	284,600
Fair Value	$16	$367

FAIR_VALUE_MEASUREMENTS_Detail3

FAIR VALUE MEASUREMENTS (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities
Derivatives	$16	$367
Recurring basis | Level 1
Assets
Total	40,342	8,079
Recurring basis | Level 1 | Money market funds
Assets
Total	40,342	8,079
Recurring basis | Level 2
Assets
Total	127,577	54,440
Recurring basis | Level 2 | Government-sponsored enterprise securities
Assets
Total	6,949	7,369
Recurring basis | Level 2 | Commercial paper
Assets
Total	10,999	5,499
Recurring basis | Level 2 | Corporate notes
Assets
Total	109,629	41,572
Recurring basis | Level 3
Liabilities
Derivatives	16	367
Recurring basis | Total
Assets
Total	167,919	62,519
Liabilities
Derivatives	16	367
Recurring basis | Total | Money market funds
Assets
Total	40,342	8,079
Recurring basis | Total | Government-sponsored enterprise securities
Assets
Total	6,949	7,369
Recurring basis | Total | Commercial paper
Assets
Total	10,999	5,499
Recurring basis | Total | Corporate notes
Assets
Total	$109,629	$41,572

FAIR_VALUE_MEASUREMENTS_Detail4

FAIR VALUE MEASUREMENTS (Details 5) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Changes in Level 3 Recurring Fair Value Measurements
Fair value of derivative liabilities at the beginning of the period		$367
Fair value of derivative liabilities at the end of the period	16	367
Derivative liabilities
Changes in Level 3 Recurring Fair Value Measurements
Fair value of derivative liabilities at the beginning of the period	367
Total Unrealized Gain Included in Earnings	-351
Fair value of derivative liabilities at the end of the period	16
Change in Unrealized Gain Related to Financial Instruments Held at the end of the period	($351)

FAIR_VALUE_MEASUREMENTS_Detail5

FAIR VALUE MEASUREMENTS (Details 6)	12 Months Ended
	Dec. 31, 2014
	item
Credit Risk
Number of financial institutions with which cash, restricted cash, cash equivalents and marketable securities are placed	4

PROPERTY_AND_EQUIPMENT_Details

PROPERTY AND EQUIPMENT (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
PROPERTY AND EQUIPMENT
Property and equipment, gross	$1,362	$1,284
Less accumulated depreciation and amortization	-1,189	-1,192
Property and equipment, net	173	92
Furniture and computer equipment
PROPERTY AND EQUIPMENT
Property and equipment, gross	1,158	1,092
Lab equipment
PROPERTY AND EQUIPMENT
Property and equipment, gross	130	118
Leasehold improvements
PROPERTY AND EQUIPMENT
Property and equipment, gross	$74	$74

EQUIPMENT_LINE_Details

EQUIPMENT LINE (Details) (Equipment financing facility, USD $)	Dec. 31, 2014
Equipment financing facility
EQUIPMENT LINE
Amount available for borrowing	$500,000

ACCRUED_LIABILITIES_Details

ACCRUED LIABILITIES (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
ACCRUED LIABILITIES
Service provider obligations	$408	$840
Clinical trial costs	513	326
Other	616	617
Accrued liabilities	$1,537	$1,783

RESTRUCTURINGS_Details

RESTRUCTURINGS (Details) (USD $)	3 Months Ended	12 Months Ended			0 Months Ended
	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 03, 2012	Apr. 25, 2013
					position	position
RESTRUCTURING
Proceeds from sales of property and equipment		$1,196,000	$170,000
Restructuring charges	430,000	1,462,000	2,702,000
Outstanding restructuring liability
Accrual balance at the end of the period	94,000	94,000
April 2013 Restructuring
RESTRUCTURING
Number of positions eliminated, inception to date						20
Restructuring charges		1,370,000
Outstanding restructuring liability
Accrual balance at the beginning of the period				94,000
Cash payments		-1,085,000		-92,000
Adjustments or non-cash credits				-2,000
Accrual balance at the end of the period	94,000	94,000
April 2013 Restructuring | One-time termination benefits
RESTRUCTURING
Restructuring charges		624,000
Outstanding restructuring liability
Stock-based compensation expense related to extension of the post-termination exercise period		28,000
April 2013 Restructuring | Employee Severance And Other Benefits
Outstanding restructuring liability
Accrual balance at the beginning of the period				21,000
Cash payments				-19,000
Adjustments or non-cash credits				-2,000
April 2013 Restructuring | Asset Write Downs
RESTRUCTURING
Restructuring charges		200,000
April 2013 Restructuring | Facility Related Charges
RESTRUCTURING
Proceeds from sales of property and equipment		1,080,000
Restructuring charges		546,000
Outstanding restructuring liability
Accrual balance at the beginning of the period				73,000
Cash payments				-73,000
Accrual balance at the end of the period	73,000	73,000
December 2012 Restructuring
RESTRUCTURING
Number of positions eliminated, inception to date					43
Restructuring charges		92,000	2,702,000		2,794,000
Outstanding restructuring liability
Cash payments		-2,271,000
December 2012 Restructuring | One-time termination benefits
RESTRUCTURING
Restructuring charges					2,523,000
Outstanding restructuring liability
Stock-based compensation expense related to extension of the post-termination exercise period					107,000
December 2012 Restructuring | Asset Write Downs
RESTRUCTURING
Restructuring charges					$271,000

DIVESTITURE_OF_STEM_CELL_ASSET1

DIVESTITURE OF STEM CELL ASSETS (Details) (USD $)	0 Months Ended
	Oct. 01, 2013	Oct. 01, 2013
DIVESTITURE OF STEM CELL ASSETS
Gain or loss recognized on assets surrendered	$0
Carrying value of stem cell assets	0	0
Series A common stock
DIVESTITURE OF STEM CELL ASSETS
Carrying value of common stock	$0	$0
Contribution Agreement | Asterias
DIVESTITURE OF STEM CELL ASSETS
Shares issued	6,537,779
Percentage ownership in Asterias	21.40%

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
COMMITMENTS AND CONTINGENCIES.
Future minimum payments under operating lease	$959,000
Rent expense under operating leases	$936,000	$1,422,000	$1,474,000
Severance Plan
COMMITMENTS AND CONTINGENCIES.
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
Severance Plan | Minimum
COMMITMENTS AND CONTINGENCIES.
Period of base salary to be considered for severance payments	2 months
Severance Plan | Maximum
COMMITMENTS AND CONTINGENCIES.
Period of base salary to be considered for severance payments	18 months

STOCKHOLDERS_EQUITY_Details

STOCKHOLDERS' EQUITY (Details) (USD $)	0 Months Ended	12 Months Ended	1 Months Ended
	Feb. 04, 2014	Dec. 31, 2014	Dec. 31, 2014
Warrants
Class of Warrant or Right, Outstanding		1,007,893	1,007,893
Underwritten Public Offering
Underwritten public offering (in shares)	25,875,000
Public offering price (in dollars per share)	$4
Net cash proceeds from public offering after deducting the underwriting discount and offering expenses	$96,805,000	$96,805,000
Warrants issued in August 2011
Warrants
Exercise Price (in dollars per share)		$3.98	3.98
Class of Warrant or Right, Outstanding		537,893	537,893
Warrants issued in April 2005
Warrants
Exercise Price (in dollars per share)		$3.75	3.75
Class of Warrant or Right, Outstanding		470,000	470,000
CIRM | Warrants issued in November 2011
Warrants
Number of warrants net exercised			461,382
Issuance of common stock upon net exercise of warrants (in shares)			168,039

STOCKHOLDERS_EQUITY_Details_2

STOCKHOLDERS' EQUITY (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
STOCKHOLDERS' EQUITY
Number of options granted with exercise price other than fair market value of Company's common stock	0	0	0
Shares Available For Grant
Balance at the beginning of the period (in shares)	16,207,250
Options granted (in shares)	-5,658,931
Awards granted (in shares)	-59,330
Options canceled/forfeited (in shares)	3,613,577
Awards canceled/forfeited (in shares)	142,375
Balance at the end of the period (in shares)	13,384,883	16,207,250
Number of Shares
Balance at the beginning of the period (in shares)	15,576,216
Options granted (in shares)	5,658,931
Options exercised (in shares)	-662,626
Options canceled/forfeited (in shares)	-3,613,577
Balance at the end of the period (in shares)	16,958,944	15,576,216
Options exercisable at the end of the period (in shares)	9,129,576	8,144,040	10,410,194
Options fully vested and expected to vest at the end of the period (in shares)	16,225,022
Weighted Average Exercise Price Per Share
Balance at the beginning of the period (in dollars per share)	$3.04
Options granted (in dollars per share)	$4.85
Options exercised (in dollars per share)	$1.94
Options canceled/forfeited (in dollars per share)	$5.48
Balance at the end of the period (in dollars per share)	$3.16	$3.04
Options exercisable at the end of the period (in dollars per share)	$3.12	$4.26	$5.49
Options fully vested and expected to vest at the end of the period (in dollars per share)	$3.14
Weighted Average Remaining Contractual Life (In years)
Balance at the end of the period	7 years 4 months 17 days
Options exercisable at the end of the period	6 years 5 months 19 days
Options fully vested and expected to vest at the end of the period	7 years 3 months 26 days
Aggregate Intrinsic Value
Balance at the end of the period (in dollars)	$16,038,000	$33,798,000
Options exercisable at the end of the period (in dollars)	9,231,000
Options fully vested and expected to vest at the end of the period (in dollars)	15,546,000
Closing stock price (in dollars per share)	$3.25
Total pretax intrinsic value of stock options exercised (in dollars)	989,000	2,787,000	100
Cash received from exercise of options (in dollars)	1,286,000	6,567,000	1,000
Income tax benefit realized from stock options exercised	$0
2002 Plan
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	4 years
Exercise price of options 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 for specific portion of options	4 years
Exercise price of options as a percentage of fair market value	100.00%
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)	13,384,883
2011 Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years
2011 Plan | First Director Option
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	3 years
Options to be granted to purchase shares upon appointment (in shares)	70,000
2011 Plan | Subsequent Director Option
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	1 year
Options to be granted to purchase shares (in shares)	35,000
1996 Directors Plan
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	3 years
Percentage of option vesting	100.00%
1996 Directors Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years
2006 Directors Plan
Shares Available For Grant
Awards canceled/forfeited (in shares)	-860,058
2006 Directors Plan | Maximum
STOCKHOLDERS' EQUITY
Expiration term of options from date of grant	10 years
2006 Directors Plan | First Director Option
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	3 years
2006 Directors Plan | Subsequent Director Option
STOCKHOLDERS' EQUITY
Vesting period for specific portion of options	1 year

STOCKHOLDERS_EQUITY_Details_3

STOCKHOLDERS' EQUITY (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014
$1.10 - $1.50
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)	$1.50
Options Outstanding
Number of Shares	4,284,937
Weighted Average Exercise Price Per Share (in dollars per share)	$1.42
Weighted Average Remaining Contractual Life (In years)	7 years 4 months 28 days
$1.51 - $2.14
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$1.51
Exercise price, high end of range (in dollars per share)	$2.14
Options Outstanding
Number of Shares	4,278,382
Weighted Average Exercise Price Per Share (in dollars per share)	$1.64
Weighted Average Remaining Contractual Life (In years)	7 years 10 months 2 days
$2.16 - $5.01
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$2.16
Exercise price, high end of range (in dollars per share)	$5.01
Options Outstanding
Number of Shares	5,376,639
Weighted Average Exercise Price Per Share (in dollars per share)	$4.29
Weighted Average Remaining Contractual Life (In years)	7 years 10 months 28 days
$5.05 To $9.32
Exercise Price Range
Exercise price, low end of range (in dollars per share)	$5.05
Exercise price, high end of range (in dollars per share)	$9.32
Options Outstanding
Number of Shares	3,018,986
Weighted Average Exercise Price Per Share (in dollars per share)	$5.80
Weighted Average Remaining Contractual Life (In years)	5 years 8 months 19 days
$1.10 - $9.32
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)	$9.32
Options Outstanding
Number of Shares	16,958,944
Weighted Average Exercise Price Per Share (in dollars per share)	$3.16
Weighted Average Remaining Contractual Life (In years)	7 years 4 months 17 days

STOCKHOLDERS_EQUITY_Details_4

STOCKHOLDERS' EQUITY (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Shares
Granted (in shares)	59,330
Canceled/forfeited (in shares)	-142,375
Restricted stock awards
Number of Shares
Non-vested restricted stock at the beginning of the period (in shares)	409,437
Granted (in shares)	59,330
Vested (in shares)	-265,422
Canceled/forfeited (in shares)	-142,375
Non-vested restricted stock at the end of the period (in shares)	60,970	409,437
Weighted Average Grant Date Fair Value Per Share
Non-vested restricted stock at the beginning of the period (in dollars per share)	$4.84
Granted (in dollars per share)	$2.67
Vested (in dollars per share)	$4.47
Canceled/forfeited (in dollars per share)	$4.66
Non-vested restricted stock at the end of the period (in dollars per share)	$4.73	$4.84
Weighted Average Remaining Contractual Term (In years)
Non-vested restricted stock at the end of the period	4 months 13 days	9 months 26 days
Other disclosures
Total fair value of restricted stock that vested	$782,000	$252,000	$936,000

STOCKHOLDERS_EQUITY_Details_5

STOCKHOLDERS' EQUITY (Details 5)	12 Months Ended
	Dec. 31, 2014
STOCKHOLDERS' EQUITY
Canceled/forfeited (in shares)	-142,375
2014 Employee Stock Purchase Plan
STOCKHOLDERS' EQUITY
Shares of common stock reserved for issuance	1,000,000
Shares issued under plan	24,375
Maximum percentage of annual salary that can be withheld	10.00%
Maximum duration of offering period	12 months
Number of offering periods in which an employee can participate at a time	1
Number of consecutive purchase periods in an offering period	2
Duration of the purchase period	6 months
Percentage applied to common stock market value in calculating purchase price under purchase plan	85.00%
Duration of the new offering period	12 months
1996 Employee Stock Purchase Plan
STOCKHOLDERS' EQUITY
Shares issued under plan	968,829
Canceled/forfeited (in shares)	231,171

STOCKHOLDERS_EQUITY_Details_6

STOCKHOLDERS' EQUITY (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$7,658,000	$4,435,000	$5,311,000
Stock options
Stock-Based Compensation Expense
Vesting period of awards	4 years
Stock-based compensation expense related to extension of the post-termination exercise period		205,000
Research and development
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	2,545,000	1,741,000	2,336,000
Restructuring charges
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses		28,000	107,000
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense included in operating expenses	$5,113,000	$2,666,000	$2,868,000

STOCKHOLDERS_EQUITY_Details_7

STOCKHOLDERS' EQUITY (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assumptions used to estimate fair value of awards
Dividends paid to date	$0
Compensation cost related to unvested stock awards not yet recognized
Compensation cost not yet recognized, net of estimated forfeitures (in dollars)	$15,032,000
Period for recognition of compensation cost on weighted average basis	27 months
Purchase Plans
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)	83.50%	50.60%	45.80%
Expected volatility range, maximum (as a percent)	166.60%	139.10%	77.40%
Risk-free interest rate range, minimum (as a percent)	0.06%	0.09%	0.06%
Risk-free interest rate range, maximum (as a percent)	0.15%	0.21%	0.21%
Additional disclosures
Weighted average estimated fair value of purchase rights (in dollars per share)	$2.10	$0.75	$0.59
Purchase Plans | Minimum
Assumptions used to estimate fair value of awards
Expected term	6 months	6 months	6 months
Purchase Plans | Maximum
Assumptions used to estimate fair value of awards
Expected term	12 months	12 months	12 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)	89.80%	74.20%	63.10%
Expected volatility range, maximum (as a percent)	92.20%	79.20%	74.00%
Risk-free interest rate range, minimum (as a percent)	1.64%	0.80%	0.81%
Risk-free interest rate range, maximum (as a percent)	1.92%	1.97%	1.25%
Expected term	5 years 6 months	6 years	6 years
Additional disclosures
Weighted average estimated fair value of employee stock options granted (in dollars per share)	$3.57	$1.03	$0.89

STOCKHOLDERS_EQUITY_Details_8

STOCKHOLDERS' EQUITY (Details 8) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-Based Compensation to Service Providers
Stock-based compensation for services by non-employees	$253,000	$252,000	$183,000
Consultants | Stock options
Stock-Based Compensation to Service Providers
Shares granted (in shares)	75,000	80,000	50,000
Stock-based compensation for services by non-employees	94,000	92,000	135,000
Consultants and Vendors | Common Stock
Stock-Based Compensation to Service Providers
Shares granted (in shares)	71,239	66,853	170,298
Stock-based compensation for services by non-employees	158,000	202,000	1,010,000
Prepaid asset relating to operating expense	$7,000

STOCKHOLDERS_EQUITY_Details_9

STOCKHOLDERS' EQUITY (Details 9)	Dec. 31, 2014	Dec. 31, 2013
STOCKHOLDERS' EQUITY
Outstanding stock options (in shares)	16,958,944	15,576,216
Options and awards available for grant (in shares)	13,384,883	16,207,250
Warrants outstanding (in shares)	1,007,893
Total (in shares)	32,327,345
2014 Employee Stock Purchase Plan
STOCKHOLDERS' EQUITY
Options and awards available for grant (in shares)	975,625

STOCKHOLDERS_EQUITY_Details_10

STOCKHOLDERS' EQUITY (Details 10) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
401(k) Plan
Matching contribution by employer (as a percent)	50.00%	75.00%	100.00%
Period of vesting of matching contributions		4 years	4 years
Service period of employees		4 years	4 years
Unvested amount under the defined-contribution savings plan to be amortized	$273,000
Geron 401K Plan
401(k) Plan
Operating expenses as a result of accelerated vesting of unvested prior employer matches for employees affected by recent restructurings		266,000	370,000
Research and development | Geron 401K Plan
401(k) Plan
Operating expense recorded for vested portion of employer matching contribution	175,000	156,000	616,000
General and administrative | Geron 401K Plan
401(k) Plan
Operating expense recorded for vested portion of employer matching contribution	$143,000	157,000	259,000

STOCKHOLDERS_EQUITY_Details_11

STOCKHOLDERS' EQUITY (Details 11) (Maximum, Sales Agreement, USD $)	0 Months Ended
	Oct. 08, 2012
Maximum | Sales Agreement
Common Stock
Aggregate offering price of common stock	$50,000,000
Maximum commission rate (as a percent)	3.00%

LICENSE_AGREEMENTS_Details

LICENSE AGREEMENTS (Details) (USD $)	0 Months Ended	12 Months Ended
	Dec. 15, 2014	Dec. 31, 2014
	item
LICENSE AGREEMENTS
Amount expected to be recognized as revenue		$35,000,000
Expected Revenue
LICENSE AGREEMENTS
Amount expected to be recognized as revenue		35,000,000
License agreements | Janssen Biotech | Initial Period
LICENSE AGREEMENTS
Upfront payment received		35,000,000
Number of agreed upon studies	2
Percentage of costs to be paid by Geron		50.00%
Percentage of costs to be paid by Janssen		50.00%
Notification period		24 months
License agreements | Janssen Biotech | U.S. Opt-In Rights exercised
LICENSE AGREEMENTS
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%
License agreements | Janssen Biotech | U.S. Opt-In Rights not exercised
LICENSE AGREEMENTS
Continuation Election milestone payment		65,000,000
Full U.S. Rights fee		70,000,000
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
License agreements | Janssen Biotech | Collaborative Arrangement Development IP Jointly Or Solely Owned
LICENSE AGREEMENTS
Percentage of costs to be paid by Geron		50.00%
Percentage of costs to be paid by Janssen		50.00%

LICENSE_AGREEMENTS_Details_2

LICENSE AGREEMENTS (Details 2) (License agreements, USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
GE Healthcare UK Limited
LICENSE AGREEMENTS
License fee revenue	$0	$825,000
TA Sciences
LICENSE AGREEMENTS
Non-refundable upfront payment recognized in other income		$2,500,000

INCOME_TAXES_Details

INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant components of deferred tax assets
Net operating loss carryforwards	$281,300,000	$271,800,000
Purchased technology		6,300,000
Research credits	23,400,000	22,700,000
Capitalized research and development	2,100,000	6,600,000
License fees	500,000	700,000
Other - net	7,600,000	10,100,000
Total deferred tax assets	314,900,000	318,200,000
Valuation allowance for deferred tax assets	-314,900,000	-318,200,000
Valuation allowance
Increase (decrease) in valuation allowance	-3,300,000	-5,500,000	14,200,000
Valuation allowance for deferred tax assets related to benefits of stock option deductions	$4,900,000

INCOME_TAXES_Details_2

INCOME TAXES (Details 2) (USD $)	Dec. 31, 2014
Domestic federal
Operating loss carryforwards
Net operating loss carryforwards	$774,000,000
State
Operating loss carryforwards
Net operating loss carryforwards	$395,000,000

INCOME_TAXES_Details_3

INCOME TAXES (Details 3) (Research and development, USD $)	Dec. 31, 2014
Domestic federal
Tax credit carryforwards
Tax credit carryforwards	$14,900,000
State
Tax credit carryforwards
Tax credit carryforwards	$13,000,000

INCOME_TAXES_Details_4

INCOME TAXES (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014
Unrecognized tax benefits
Unrecognized tax benefits, if recognized would impact effective tax rate	$17,100,000
Balance at the beginning of the period	11,600,000
Increase related to prior year tax positions	5,100,000
Increase related to current year tax positions	400,000
Balance at the end of the period	17,100,000
Interest and penalties expense related to unrecognized tax benefits	$0

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details)	12 Months Ended
	Dec. 31, 2014
	item
SEGMENT INFORMATION
Number of operating segments	1

CONSOLIDATED_STATEMENTS_OF_CAS3

CONSOLIDATED STATEMENTS OF CASH FLOWS DATA (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Operating Activities:
Issuance of common stock for services rendered to date or to be received in future periods			$69
Issuance of common stock for 401(k) matching contributions	313	839	1,361
Reclassification between deposits and other current assets	190	219	526
Supplemental Investing Activities:
Net unrealized loss on marketable securities	($70)	($54)	($38)

SELECTED_QUARTERLY_FINANCIAL_I2

SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
SELECTED QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
Revenues	$178,000	$160,000	$341,000	$474,000	$225,000	$181,000	$112,000	$765,000
Operating expenses	9,189,000	10,067,000	9,004,000	9,205,000	9,500,000	8,914,000	9,077,000	12,750,000	37,465,000	40,241,000	74,467,000
Net loss	-8,947,000	-9,549,000	-8,734,000	-8,440,000	-9,281,000	-8,254,000	-8,947,000	-11,897,000	-35,670,000	-38,379,000	-68,881,000
Basic and diluted net loss per share (in dollars per share)	($0.06)	($0.06)	($0.06)	($0.06)	($0.07)	($0.06)	($0.07)	($0.09)	($0.23)	($0.30)	($0.54)
Restructuring charges					$430,000					$1,462,000	$2,702,000

SUBSEQUENT_EVENT_Details

SUBSEQUENT EVENT (Details) (Subsequent event, USD $)	0 Months Ended	12 Months Ended
	Mar. 03, 2015	Dec. 31, 2015
	position	position
Subsequent event
SUBSEQUENT EVENT
Number of positions before organizational resizing	39
Number of positions after organizational resizing	21
Restructuring workforce reduction percentage	46.00%
Aggregate potential restructuring charges		$1,900,000
Expected cash payments		$1,500,000
Number of positions eliminated		18