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 2, 2018

MIRATI THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

9393 Towne Centre Drive, Suite 200

San Diego, California 92121

(Address of principal executive offices and zip code)

Registrant’s telephone number, including area code: (858) 332-3410

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):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☒

On August 2, 2018, the Company entered into a Third Amendment to Lease Agreement (the “Amendment”) with ARE-SD Region No. 20 (the “Landlord”) to amend the Lease Agreement, dated June 24, 2014, the First Amendment to Lease dated March 23, 2017, and the Second Amendment to Lease dated April 5, 2018 (the “Amended Lease”) between the Company and Landlord. The Amendment expands the size of the existing premises by adding approximately 6,100 square feet of space for an additional base rent of $4,000 per month through January 31, 2020. In addition, our share of operating expenses of the building in which the premises are located, has increased from approximately 43% to 58%. All other material terms and covenants from the Amended Lease remain unchanged.

A copy of the Amendment is filed as Exhibit 10.1 to this report and the description of the terms of the Amendment is qualified in its entirety by reference to such exhibit.

(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.