UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 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): May 29, 2014

diaDexus, Inc.

(Exact Name of Registrant as Specified in its Charter)

349 Oyster Point Boulevard, South San Francisco, California 94080

(Address of Principal Executive Offices) (Zip Code)

Registrant’s telephone number, including area code: (650) 246-6400

N/A

(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:

On May 29, 2014, the stockholders of diaDexus, Inc. (the “Company”) approved an amendment to the 2012 Equity Incentive Award Plan (the “2012 Plan”) to add 4,000,000 shares of common stock to the existing reserve under the Plan. The amendment to the 2012 Plan was approved by the Board of Directors of the Company (the “Board”) on March 21, 2014, subject to stockholder approval at the 2014 Annual Meeting of Stockholders (the “2014 Annual Meeting”).

The 2012 Plan initially became effective on May 17, 2012. The 2012 Plan provides for the grant of stock options (both incentive stock options and nonqualified stock options), restricted stock, stock appreciation rights, performance awards, stock payments, deferred stock, deferred stock units, restricted stock units, and performance-based awards (collectively, “equity awards”) to eligible participants. The Board and the compensation committee of the Board share the authority to administer the 2012 Plan. The plan administrator has the authority to designate the persons to whom equity awards will be granted, determine the number of shares of common stock to be subject to each equity award, determine the time or times during the term of each equity award within which all or a portion of the award may be exercised, amend the 2012 Plan, and construe and interpret the terms of the 2012 Plan. The Company may grant equity awards authorized under the 2012 Plan to its employees, directors and consultants of the Company and its affiliates. Accordingly, all of the Company’s employees and non-employee directors are eligible to participate in the 2012 Plan.

As of March 31, 2014, 2,184,214 shares of Common Stock were available for future grants under the 2012 Plan. Prior to the amendment of the 2012 Plan, the aggregate number of shares that could be issued under the 2012 Plan consisted of the sum of (i) the 3,000,000 shares that stockholders approved in May 2012, (ii) the 1,685,492 shares that remained available for new grants under the Company’s stock plans and non-plan award agreements (the “prior plans”) that were outstanding, which, on approval of the 2012 Plan, ceased to be available under those prior plans and agreements and (iii) up to 10,318,904 shares that were subject to awards outstanding under the prior plans as of March 31, 2014 that terminate, expire or lapse. As of March 31, 2014, of the 15,004,396 shares originally made subject to the reserve, 2,974,687 shares have been issued or otherwise failed to return to the 2012 Plan, such that only 12,029,709 shares of common stock are reserved and available for issuance under the 2012 Plan (including the 9,841,195 shares subject to outstanding awards). Generally, shares subject to an award that terminates, expires or lapses for any reason are made available for issuance again under the 2012 Plan.

The above description of the 2012 Plan is a summary only and is qualified in its entirety by reference to the complete text of the 2012 Plan, as amended, which is attached hereto as Exhibit 10.1 and incorporated herein by reference.

The 2014 Annual Meeting of the Company was held at 1:00 p.m. Pacific Daylight Time on May 29, 2014 at the Company’s principal executive offices in South San Francisco, California. The final voting results for the matters submitted to a vote of stockholders at the 2014 Annual Meeting are as follows:

(d) Exhibits

SIGNATURES

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