Stockholders’ Equity

Preferred Stock

The Company has 10,000,000 shares of preferred stock authorized for issuance, par value of $0.001 per share. As of December 31, 2017 and 2016, no shares of preferred stock were issued and outstanding.

Common Stock

The Company has 50,000,000 shares of common stock authorized for issuance, par value of $0.001 per share. Holders of the Company’s common stock are entitled to one vote per share. As of December 31, 2017 and 2016, there were 34,807,509 and 24,813,169 shares of common stock issued and outstanding.

The following table presents common stock reserved for future issuance for the following equity instruments as of December 31, 2017 and 2016 (in thousands):



	December 31,
	2017	2016
Stock options and restricted stock units outstanding	3,651	3,388
Warrants to purchase common stock	38	1,975
Available for future issuance under equity and purchase plans	872	952
	4,561	6,315

Sale of Common Stock

In May 2016, the Company entered into an at-the-market sales agreement (the “ATM Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) and filed a registration statement (File No. 333-211265) and a prospectus for the offer and sale of up to $25.0 million of shares of its common stock from time to time. In August and September 2017, the Company sold a total of 1,550,880 shares of its common stock under the ATM Agreement resulting in net proceeds of approximately $19.4 million, after deducting underwriting discounts and commissions and other offering expenses. In December 2017, the Company filed a prospectus supplement under its shelf registration statement (File No. 333-220759), for the offer and sale of up to $75.0 million of shares of its common stock from time to time pursuant to the ATM Agreement. Cantor is entitled to a commission at a fixed commission rate of up to 3.0% of the gross proceeds of the sales price of all common stock sold under the ATM Agreement. The Company and Cantor may each terminate the ATM Agreement at any time upon ten days’ prior notice. To date, the Company has not sold any shares of common stock under the 2017 prospectus supplement pursuant to the ATM Agreement.

In October 2017, the Company completed an underwritten public offering of 7.7 million shares of its common stock, which included 1.0 million shares of common stock issued upon the exercise in full of the option to purchase additional shares granted to the underwriters in the offering. The shares were sold to the public at an offering price of $37.50 per share. Net proceeds raised from the offering amounted to approximately $271.3 million, after deducting underwriting discounts and commissions and other offering expenses.

Warrants to Purchase Common Stock

Outstanding warrants to purchase common stock at December 31, 2016 included warrants sold as part of the Company’s 2012 public offering. The warrants were exercisable into 1,901,918 shares of the Company’s common stock at an exercise price of $20.00 per share and had a contractual term of 5 years from the issuance date. In July 2017, these warrants expired unexercised. As of December 31, 2017, the Company had outstanding warrants exercisable into 37,840 shares of the Company’s common stock with a weighted-average exercise price of $76.11 per share.