STOCKHOLDERS' EQUITY (Tables)

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

				Outstanding Options
									Weighted Average	Aggregate
	Shares						Weighted Average		Remaining	Intrinsic
	Available			Number of			Exercise Price		Contractual Life	Value
	For Grant			Shares			Per Share		(In years)	(In thousands)
Balance at December 31, 2016		9,570,535			19,125,287		$	3.15
Options granted		(3,484,000	)		3,484,000		$	2.19
Awards granted		(72,066	)		—		$	—
Options exercised		—			(12,500	)	$	1.41
Options cancelled/forfeited		188,258			(188,258	)	$	7.99
Balance at December 31, 2017		6,202,727			22,408,529		$	2.96	6.24	$	2,034
Options exercisable at December 31, 2017					17,249,032		$	3.03	5.57	$	2,034
Options fully vested and expected to vest at December 31, 2017					22,171,142		$	2.96	6.21	$	2,034

8. STOCKHOLDERS’ EQUITY (Continued)

Information about stock options outstanding as of December 31, 2017 is as follows:

	Options Outstanding
					Weighted Average
			Weighted Average		Remaining
	Number of		Exercise Price		Contractual Life
Exercise Price Range	Shares		Per Share		(In years)
$1.10 - $1.51		5,655,662	$	1.45		4.89
$1.55 - $2.16		5,631,031	$	2.08		7.04
$2.22 - $4.34		6,000,783	$	3.37		7.60
$4.42 - $7.31		5,121,053	$	5.10		5.27
$1.10 - $7.31		22,408,529	$	2.96		6.24

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

				Weighted Average		Weighted Average
				Grant Date		Remaining
	Number of			Fair Value		Contractual Term
	Shares			Per Share		(In years)
Non-vested restricted stock at December 31, 2016		—		$	—		—
Granted		72,066		$	2.20
Vested		(72,066	)	$	2.20
Non-vested restricted stock at December 31, 2017		—		$	—		—

	Year Ended December 31,
(In thousands)	2017		2016		2015
Research and development	$	988	$	1,275	$	2,139
Restructuring charges		—		—		307
General and administrative		7,156		6,970		5,951
Stock-based compensation expense included in operating expenses	$	8,144	$	8,245	$	8,397

The fair value of stock options granted in 2017, 2016 and 2015 has been estimated at the date of grant using the Black Scholes option‑pricing model with the following assumptions:

	Year Ended December 31,
	2017	2016	2015
Dividend yield	0%	0%	0%
Expected volatility range	0.884 to 0.892	0.888 to 0.890	0.874 to 0.884
Risk-free interest rate range	1.98% to 1.99%	1.21% to 1.38%	1.68% to 1.71%
Expected term	5.5 yrs	5.5 yrs	5.5 yrs

8. STOCKHOLDERS’ EQUITY (Continued)

The fair value of employee stock purchases in 2017, 2016 and 2015 has been estimated using the Black Scholes option‑pricing model with the following assumptions:

	Year Ended December 31,
	2017	2016	2015
Dividend yield	0%	0%	0%
Expected volatility range	0.577 to 0.641	0.641 to 0.684	0.654 to 1.392
Risk-free interest rate range	0.45% to 0.89%	0.28% to 0.45%	0.11% to 0.28%
Expected term range	6 - 12 mos	6 - 12 mos	6 - 12 mos

Common stock reserved for future issuance as of December 31, 2017 is as follows:

Outstanding stock options			22,408,529
Options and awards available for grant			6,202,727
Employee stock purchase plan			895,308
Warrant outstanding			537,893
Total			30,044,457