Note 9 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Year Ended December 31,
	2019		2018
Research and development	$	233	$	1,142
General and administrative		710		2,287
Total	$	943	$	3,429

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
	2019			2018
Weighted average expected volatility		89.6	%		93.5	%
Expected term (in years)		6.10			6.07
Risk free interest rate		2.60	%		2.55	%
Expected dividend yield		0	%		0	%

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		114,931		$	204.76		7.4	$	404
Granted		29,562		$	106.32
Exercised		-		$	-
Forfeited		(80,431	)	$	124.40
Expired		(63,951	)	$	260.40
Outstanding at December 31, 2019		111		$	218.40		0.1	$	-
Exercisable at December 31, 2019		111		$	218.40		0.1	$	-
Vested or expected to vest at December 31, 2019 (1)		111		$	218.40		0.1	$	-