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): September 6, 2016

SORRENTO THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

9380 Judicial Drive

San Diego, CA 92121

(Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 210-3700

(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:

(a) Dismissal of Independent Registered Public Accounting Firm

On September 6, 2016, the Audit Committee (the “Audit Committee”) of the Board of Directors of Sorrento Therapeutics, Inc., a Delaware corporation (the “Registrant” or the “Company”), dismissed Mayer Hoffman McCann P.C. (“MHM”) as the Registrant’s independent registered public accounting firm.

The reports of MHM on the Registrant’s consolidated financial statements for the fiscal years ended December 31, 2015 and 2014 did not contain an adverse opinion or a disclaimer of opinion and were not qualified or modified as to uncertainty, audit scope or accounting principles.

During the fiscal years ended December 31, 2015 and 2014 and the subsequent interim period through September 2, 2016, there have been no “disagreements” (as defined in Item 304(a)(1)(iv) of Regulation S-K and related instructions) with MHM on any matter of accounting principles or practices, financial statement disclosure or auditing scope or procedure, which disagreements, if not resolved to the satisfaction of MHM, would have caused MHM to make reference thereto in their reports on the consolidated financial statements for such fiscal years. During the fiscal years ended December 31, 2015 and 2014 and any subsequent interim period through September 2, 2016, there have been no “reportable events” (as defined in Item 304(a)(1)(v) of Regulation S-K).

The Registrant provided MHM with a copy of the disclosure it is making herein in response to Item 304(a) of Regulation S-K and requested that MHM furnish the Registrant with a copy of its letter addressed to the Securities and Exchange Commission (the “SEC”), pursuant to Item 304(a)(3) of Regulation S-K, stating whether or not MHM agrees with the statements related to them made by the Registrant in this report. A copy of MHM’s letter to the SEC dated September 6, 2016 is attached as Exhibit 16.1 to this report.

(b) Engagement of Independent Registered Public Accounting Firm

On September 6, 2016, the Registrant’s Audit Committee, approved the appointment of Deloitte & Touche LLP (“Deloitte”) as the Registrant’s new independent registered public accounting firm, effective immediately. During the fiscal years ended December 31, 2015 and 2014 and the subsequent interim period through September 2, 2016, neither the Registrant, nor anyone on its behalf, consulted Deloitte regarding either (i) the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the financial statements of the Registrant, and no written report or oral advice was provided to the Registrant by Deloitte that Deloitte concluded was an important factor considered by the Registrant in reaching a decision as to any accounting, auditing or financial reporting issue; or (ii) any matter that was either the subject of a “disagreement” (as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions) or a “reportable event” (as that term is defined in Item 304(a)(1)(v) of Regulation S-K).

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.

Dated: September 7, 2016