SHARE-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

A summary of Common Stock option activity is as follows:


	Number of Options (in thousands)	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)












Outstanding at December 31, 2019	3,497	$	5.19	5.91	$	—
Granted	2,505	$	0.89
Exercised	(17)	$	0.76
Forfeited or expired	(826)	$	4.84
Outstanding at June 30, 2020	5,159	$	3.17	6.86	$	633,352
Vested or expected to vest at June 30, 2020	5,159	$	3.17	6.86	$	633,352
Exercisable as of June 30, 2020	2,328	$	4.70	5.28	$	34,819
Vested as of June 30, 2020	2,328	$	4.70	5.28	$	34,819

Fair Value Assumptions for Stock Options

The fair value was determined by the Black-Scholes option pricing model using the following weighted-average assumptions:


	Six Months Ended June 30,
	2020			2019
Expected term, in years	4.82			6.36
Expected volatility	99.3		%	98.8		%
Risk-free interest rate	0.8		%	2.5		%
Expected dividend yield	—		%	—		%
Weighted-average exercise price	$	0.89		$	2.99

Allocation of Share-based Compensation Expense

Share-based compensation related to all equity awards issued pursuant to the 2008 Plan and 2016 Plan and for estimated shares to be issued under the ESPP for the purchase periods active during each respective period is included in the condensed consolidated statements of operations and comprehensive loss as follows:


	Six Months Ended June 30,
	2020		2019
	(in thousands)
Research and development	$	357	$	809
General and administrative	930		1,284
Total share-based compensation expense	$	1,287	$	2,093