The Company’s Amended and Restated 2015 Stock Incentive Plan (the “2015 Plan”), is administered by the Company’s board of directors and provides for the grant of incentive stock options, nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s officers, employees, consultants, advisors and directors are eligible to receive awards under the 2015 Plan; however, incentive stock options may only be granted to employees. Stock option awards are exercisable for a period determined by the Company, but in no event longer than ten years from the date of the grant. Stock option awards generally vest as to 25% of the shares underlying the option on the first anniversary of the date of grant and as to 6.25% of the shares underlying the option quarterly thereafter for the following three years, subject to continued service. In May 2018, the Company’s stockholders approved an amendment and restatement of the 2015 Plan which included an 8,200 increase to the number of shares of common stock that may be issued pursuant to the 2015 Plan. There were 8,535 shares available to be granted under the 2015 Plan as of September 30, 2019.

A summary of the status of the Company’s stock option activity for the nine months ended September 30, 2019 is presented in the table and narrative below:

	Options			Weighted Average Exercise Price
Outstanding at January 1, 2019		14,950		$	5.14
Granted		5,398			2.28
Exercised		(1,142	)		3.34
Cancelled/Forfeited		(4,227	)		6.61
Outstanding at September 30, 2019		14,979		$	3.83
Options exercisable at September 30, 2019		6,139		$	5.46
Weighted-average fair value of options granted during the period				$	1.59

The Company utilizes the Black-Scholes option pricing model for determining the estimated fair value for stock-based awards. The Black-Scholes model requires the use of assumptions which determine the fair value of the stock-based awards. The assumptions used to value options granted are as follows:

	Nine Months Ended
	September 30, 2019			September 30, 2018
Expected term of option	5.6 - 6.0 years			6.0 years
Expected volatility	73% - 82%			79% - 80%
Risk free interest rate	1.41% - 2.60%			2.62% - 2.98%
Expected dividend yield		0	%		0	%

Total compensation expense recorded in the accompanying statements of operations associated with stock option grants made to employees was $1,688 and $1,506 for the three months ended September 30, 2019 and 2018, respectively, and $4,655 and $7,281 for the nine months ended September 30, 2019 and 2018, respectively. Total compensation expense recorded in the accompanying statements of operations associated with stock option grants made to consultants was $0 and $89 for the three months ended September 30, 2019 and 2018, respectively, and $154 and $161 for the nine months ended September 30, 2019 and 2018, respectively. The Company recorded no tax benefit related to these stock options since the Company currently maintains a full valuation allowance on its deferred tax assets.

As of September 30, 2019, the intrinsic value of the stock options outstanding was $10,501, of which $1,764 related to vested stock options and $8,737 related to unvested stock options. The intrinsic value of stock options is calculated based on the difference between the exercise prices of the underlying common stock and the quoted stock price of the Company’s common stock as of the reporting date.

As of September 30, 2019, the total compensation cost related to unvested stock options not yet recognized in the financial statements was approximately $12,719, net of estimated forfeitures, and the weighted average period over which this amount is expected to be recognized is 2.8 years.