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STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2018

Schedule of aggregate option and award activity

Aggregate option and award activity for the 2002 Plan, 2011 Plan, 2018 Plan, 2006 Directors Plan, Inducement Plan and Directors Market Plan is as follows:

				Outstanding Options
										Weighted Average		Aggregate
	Shares							Weighted Average		Remaining		Intrinsic
	Available			Number of				Exercise Price		Contractual Life		Value
	For Grant			Shares				Per Share		(In years)		(In thousands)
Balance at December 31, 2017		6,202,727			22,408,529			$	2.96
Additional shares authorized		14,000,000			—			$	—
Options granted		(9,265,000	)		9,265,000		⁽¹⁾	$	2.07
Awards granted		(139,652	)		—			$	—
Options exercised		—			(3,144,878	)		$	2.20
Options cancelled/forfeited/expired		1,166,324			(1,242,699	)		$	3.48
Balance at December 31, 2018		11,964,399			27,285,952		⁽¹⁾	$	2.72		6.71	$	—
Options exercisable at December 31, 2018					16,464,746			$	3.13		5.10	$	—
Options fully vested and expected to vest at December 31, 2018					26,293,625			$	2.75		6.61	$	—

(1)	Includes 4,500,000 performance-based stock options that have not achieved certain strategic milestones.

Schedule of information about stock options outstanding by exercise price range

Information about stock options outstanding as of December 31, 2018 is as follows:

	Options Outstanding
						Weighted Average
				Weighted Average		Remaining
	Number of			Exercise Price		Contractual Life
Exercise Price Range	Shares			Per Share		(In years)
$1.10 - $1.72		10,290,050		$	1.61		7.04
$1.73 - $2.45		7,144,384		$	2.27		7.65
$2.54 - $5.01		8,055,105		$	3.95		6.06
$5.09 - $7.31		1,796,413		$	5.33		4.03
$1.10 - $7.31		27,285,952	⁽¹⁾	$	2.72		6.71

(1)	Includes 4,500,000 performance-based stock options that have not achieved certain strategic milestones.

Schedule of aggregate restricted stock activity

Aggregate restricted stock activity for the 2011 Plan and the 2018 Plan is as follows:

				Weighted Average		Weighted Average
				Grant Date		Remaining
	Number of			Fair Value		Contractual Term
	Shares			Per Share		(In years)
Non-vested restricted stock at December 31, 2017		—		$	—		—
Granted		73,980		$	1.91
Vested		(73,980	)	$	1.91
Non-vested restricted stock at December 31, 2018		—		$	—		—

Summary of allocation of stock-based compensation expense related to share-based payment awards

	Year Ended December 31,
(In thousands)	2018		2017		2016
Research and development	$	949	$	988	$	1,275
General and administrative		5,419		7,156		6,970
Stock-based compensation expense included in operating expenses	$	6,368	$	8,144	$	8,245

Schedule of assumptions used to estimate the fair value of stock options granted

The fair value of stock options granted in 2018, 2017 and 2016 has been estimated at the date of grant using the Black Scholes option‑pricing model with the following assumptions:

	Year Ended December 31,
	2018	2017	2016
Dividend yield	0%	0%	0%
Expected volatility range	0.821 to 0.990	0.884 to 0.892	0.888 to 0.890
Risk-free interest rate range	2.55% to 3.11%	1.98% to 1.99%	1.21% to 1.38%
Expected term range	5.25 - 6.62 yrs	5.5 yrs	5.5 yrs

Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan

The fair value of employee stock purchases in 2018, 2017 and 2016 has been estimated using the Black Scholes option‑pricing model with the following assumptions:

	Year Ended December 31,
	2018	2017	2016
Dividend yield	0%	0%	0%
Expected volatility range	0.437 to 0.475	0.577 to 0.641	0.641 to 0.684
Risk-free interest rate range	1.53% to 1.76%	0.45% to 0.89%	0.28% to 0.45%
Expected term range	6 - 12 mos	6 - 12 mos	6 - 12 mos

Schedule of common stock reserved for future issuance

Common stock reserved for future issuance as of December 31, 2018 is as follows:

Outstanding stock options			27,285,952
Options and awards available for grant			11,964,399
Employee stock purchase plan			876,908
Warrant outstanding			537,893
Total			40,665,152