UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): June 8, 2015

SUNESIS PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (650) 266-3500

Not Applicable

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Item 5.07. Submission of Matters to a Vote of Security Holders.

The 2015 Annual Meeting of Stockholders, or the Annual Meeting, was held on June 8, 2015. Proxies for the Annual Meeting were solicited by the Board of Directors pursuant to Section 14(a) of the Securities Exchange Act of 1934, as amended, and there was no solicitation in opposition to the Board of Directors’ solicitation. There were 70,617,432 shares of common stock entitled to vote at the Annual Meeting. A total of 58,562,147 shares were represented at the Annual Meeting in person or by proxy. The final votes on the proposals presented at the meeting were as follows:

Proposal No. 1

Steve R. Carchedi, Helen S. Kim and Dayton Misfeldt were elected as Class I directors to hold office until the 2018 Annual Meeting of Stockholders by the following vote:

In addition to the directors elected above, James W. Young, Steve B. Ketchum and Homer L. Pearce will continue to serve as Class II directors until the 2016 Annual Meeting of Stockholders and until their successors are elected and have qualified, or until their earlier death, resignation or removal. Matthew K. Fust, David C. Stump and Daniel N. Swisher, Jr. will continue to serve as Class III directors until the 2017 Annual Meeting of Stockholders and until their successors are elected and have qualified, or until their earlier death, resignation or removal.

Proposal No. 2

The vote, on an advisory basis, of the compensation of our named executive officers as disclosed in the 2015 proxy statement, filed with the Securities and Exchange Commission on April 28, 2015, was approved by the following vote:

Proposal No. 3

The selection by the Audit Committee of the Board of Directors of Ernst & Young LLP as our independent registered public accounting firm for the year ending December 31, 2015 was ratified by the following vote:

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.