TSRO Tesaro, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 10-Q/A

Amendment No. 1

(Mark One)

For the quarterly period ended September 30, 2016

OR

For the transition period from          to          

Commission file number 001-35587

(339) 970-0900

(Registrant’s Telephone Number, Including Area Code)

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.  Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).  Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company.  See the definitions of “large accelerated filer”, “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).  Yes ☐ No ☒

As of October 31, 2016 there were 51,662,407 shares of the registrant’s Common Stock, par value $0.0001 per share, outstanding.

Explanatory Note

TESARO, Inc., or the Company, is filing this Amendment No. 1, or this Amendment, to its Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2016, or the Original Form 10-Q, as an exhibit-only filing to re-file Exhibit 10.1 to the Original Form 10-Q, or the Exhibit, in response to comments the Company received from the Securities and Exchange Commission on a confidential treatment request the Company made for certain portions of the Exhibit. 

In addition, as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended, new certifications by the Company’s principal executive officer and principal financial officer are filed as exhibits to this Amendment.    

Except as described above, this Amendment does not reflect events occurring after the filing of the Original Form 10-Q and no revisions are being made pursuant to this Amendment to the Company’s financial statements or any other disclosure contained in the Original Form 10-Q.  Accordingly, this Amendment should be read in conjunction with the Original Report.