Note 6 - Stock-based Compensation

3 Months Ended

Mar. 31, 2017

Notes to Financial Statements

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

6. Stock-based Compensation

Stock Options

The following table summarizes stock option activity for employees and non-employees:

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2016		2,166,254		$	8.55		7.1	$	124
Granted		659,342		$	2.05
Exercised		(74,001	)	$	1.45
Outstanding at March 31, 2017		2,751,595		$	7.18		7.6	$	64
Exercisable at March 31, 2017		1,242,299		$	7.35		6.0	$	64
Vested or expected to vest at March 31, 2017 (1)		2,751,595		$	7.18		7.6	$	64

___________________

(1)

Represents the number of vested options at

March

31,

2017

plus the number of unvested options expected to vest based on the unvested options outstanding at

March

31,

2017.

Employee Stock Purchase Plan

The

2014

Employee Stock Purchase Plan (ESPP) initially authorized the issuance of up to

140,500

shares of Common Stock. The number of shares increases each

January

1,

commencing on

January

1,

2015

and ending on (and including)

January

1,

2024,

by an amount equal to the lesser of

one

percent of the outstanding shares as of the end of the immediately preceding fiscal year,

281,000

shares, or any lower amount determined by the Company’s Board of Directors prior to each such

January

1st.

The Company’s Board of Directors has determined there was to be no increase on

January

1,

2017.

As of

March

31,

2017,

the

2014

ESPP authorized the issuance of up to

304,991

shares of Common Stock. The

fifth

offering under the

2014

ESPP began on

January

1,

2017

and ends on

June

30,

2017.

No

shares were issued during the

three

months ended

March

31,

2017

under the

2014

ESPP.

Common Stock

The Company has the following shares reserved for future issuance:

	March 31, 2017		December, 31 2016
Stock-based compensation awards		3,572,611		2,982,470
Employee Stock Purchase Plan		292,821		292,821
Total		3,865,432		3,275,291