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): August 11, 2011

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):

On August 11, 2011, we entered into a controlled equity offering sales agreement with Cantor Fitzgerald & Co., or Cantor, pursuant to which we may issue and sell shares of our common stock having an aggregate offering price of up to $20.0 million from time to time through Cantor acting as agent and/or principal. This sales agreement does not supersede our existing controlled equity offering sales agreement with Cantor, dated April 29, 2010, under which $2.0 million of our common stock remained available to be sold as of June 30, 2011. Sales of our common stock through Cantor, if any, will be made on The NASDAQ Capital Market by means of ordinary brokers’ transactions at market prices, in block transactions or as otherwise agreed by Cantor and us. Cantor will use its commercially reasonable efforts to sell our common stock from time to time, based upon our instructions (including any price, time or size limits or other customary parameters or conditions we may impose). We will pay Cantor a commission rate of 3.0% of the gross sales price per share of any common stock sold through Cantor as agent under the sales agreement. We have also provided Cantor with customary indemnification rights.

Under the terms of the sales agreement, we may also sell shares of our common stock to Cantor as principal for its own account, at a price negotiated at the time of sale. If we sell shares to Cantor in this manner, we will enter into a separate agreement setting forth the terms of any such transactions.

The foregoing description of the sales agreement is not complete and is qualified in its entirety by reference to the full text of such agreement, a copy of which is filed herewith as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference. This Current Report on Form 8-K also incorporates by reference the sales agreement into our shelf registration statements on Form S-3 (File Nos. 333-164025 and 333-166366) previously filed with the SEC.

On August 11, 2011, we reported our financial results for the three months ended June 30, 2011. A copy of the press release issued concerning the foregoing results is furnished herewith as Exhibit 99.1 and is incorporated herein by reference.

The press release is furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended. The information contained herein and in the accompanying exhibit shall not be incorporated by reference into any filing with the U.S. Securities and Exchange Commission made by Sunesis, whether made before or after the date hereof, regardless of any general incorporation language in such filing.

(d) Exhibits

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.

EXHIBIT INDEX