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): March 12, 2013

SPECTRUM PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (702) 835-6300

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:

On March 12, 2013, Spectrum Pharmaceuticals, Inc. (the “Company”) issued a corporate update by press release, which, among other matters, contained forward looking statements with respect to the future performance of the Company and its products. As with all forward looking statements, there can be no assurance that such results will be achieved.

Forward-looking statement — This Form 8-K contains forward-looking statements regarding future events and the future performance of Spectrum Pharmaceuticals that involve risks and uncertainties that could cause actual results to differ materially. These statements are based on management’s current beliefs and expectations. These statements include, but are not limited to, statements that relate to our business and its future, including sales of Spectrum’s drug products, leveraging the expertise of partners and employees around the world to assist us in the execution of our strategy, and any statements that relate to the intent, belief, plans or expectations of Spectrum or its management, or that are not a statement of historical fact. Risks that could cause actual results to differ include our lack of sustained revenue history, our limited marketing experience, our customer concentration, the possibility customer buying patterns may change, evolving market dynamics, our dependence on third parties for clinical trials, manufacturing, distribution and quality control, risks related to drug development and other risks that are described in further detail in the Company’s reports filed with the Securities and Exchange Commission. We do not plan to update any such forward-looking statements and expressly disclaim any duty to update the information contained in this Form 8-K except as required by law.

The information in this Current Report on Form 8-K is furnished pursuant to Item 7.01 and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liability of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such a filing.

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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.

Date: March 12, 2013

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EXHIBIT INDEX

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