Quarterly report pursuant to Section 13 or 15(d)

Stock Plans

Stock Plans

9 Months Ended

Sep. 30, 2017

2. Stock Plans

The following table summarizes the stock-based compensation expense recorded for awards under the stock option plans for the three and nine-month periods ended September 30, 2017 and 2016:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in thousands, except per share amounts)	2017		2016		2017		2016
Research and development	$	134	$	85	$	379	$	302
General and administrative		270		117		828		481
Total stock-based compensation expenses	$	404	$	202	$	1,207	$	783

No tax benefit was recognized related to stock-based compensation expense since we have accumulated operating losses and we have established a full valuation allowance to offset all the potential tax benefits associated with our deferred tax assets.

We use the Black-Scholes-Merton option-pricing model with the following assumptions to estimate the stock-based compensation expense for the three and nine-month periods ended September 30, 2017 and 2016:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2017			2016			2017			2016
Weighted-average risk-free interest rate		2.0	%		1.5	%		2.1	%		1.5	%
Expected dividend payments		—			—			—			—
Expected holding period (years) ¹		6.6			6.5			6.6			6.5
Weighted-average volatility factor ²		0.88			0.92			0.88			0.92
Estimated forfeiture rates ³		26	%		29	%		27	%		29	%

(1)

Expected holding period is based on historical experience of similar awards, giving consideration to the contractual terms of the stock-based awards, vesting schedules and the expectations of future employee behavior.

(2)

Weighted average volatility is based on the historical volatility of our common stock.

(3)

Estimated forfeiture rates are based on historical data.

Options to purchase approximately 50,000 shares of common stock were granted during the three-month period ended September 30, 2017. No options were granted during the three-month period ended September 30, 2016. Options to purchase approximately 546,000 and 168,000 shares of common stock were granted during the nine-month periods ended September 30, 2017 and 2016, respectively.

The following table summarizes option activity for the nine-month period ended September 30, 2017:

					Weighted
			Weighted		Average
			Average		Remaining		Aggregate
			Exercise		Option		Intrinsic
(in thousands, except per share amounts)	Options		Price		Term		Value
Outstanding at January 1, 2017		2,002	$	5.67		5.68	$	203
Granted		546		3.50
Exercised		—		—
Expired		(27)		12.83
Cancelled or forfeited		(113)		5.27

Outstanding at September 30, 2017		2,408	$	5.12		5.93	$	12

Exercisable at September 30, 2017		1,962	$	5.46		5.17	$	—

No shares of restricted stock were awarded to employees, directors and consultants during the three and nine-month periods ended September 30, 2017 and 2016.

As of September 30, 2017, there was approximately $0.8 million of total unrecognized compensation expense related to non-vested stock options. This expense is expected to be recognized over a weighted-average period of 1.2 years.