Sec Form 4 Filing - ORONSKY ARNOLD L @ TESARO, Inc. - 2016-03-18

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person ORONSKY ARNOLD L 2. Issuer Name and Ticker or Trading Symbol TESARO, Inc. [ TSRO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O TESARO, INC., 1000 WINTER STREET, SUITE 3300 3. Date of Earliest Transaction (MM/DD/YY) 03/18/2016 (Street) WALTHAM, MA02451 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/18/2016 P 142,085 ( 1 ) A $ 35.19 2,013,786 I By partnership ( 2 ) Common Stock 6,614 ( 3 ) I By partnership ( 4 ) Common Stock 1,003 ( 5 ) I By corporation ( 6 ) Common Stock 2,479 ( 3 ) ( 5 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ORONSKY ARNOLD L C/O TESARO, INC. 1000 WINTER STREET, SUITE 3300 WALTHAM, MA02451 X Signatures /s/ Karen A. Wilson, Attorney-in-Fact 03/18/2016 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares were acquired upon the closing of a private placement that was publicly disclosed by the Issuer on February 25, 2016. ( 2 )The shares are owned by InterWest Partners X, LP ("IW10"). The Reporting Person is a managing director of InterWest Management Partners X, LLC ("IMP10"), the general partner of IW10, and disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. ( 3 )This number reflects that 6,614 shares previously reported as being owned directly were assigned to IMP10. ( 4 )The shares are beneficially owned by IMP10. The Reporting Person is a managing director of IMP10, and disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. ( 5 )This number reflects that 1,003 shares previously reported as being owned directly were assigned to InterWest Venture Management Company ("IVMC"). ( 6 )The shares are beneficially owned by IVMC. The Reporting Person is an officer and director of IVMC and may be deemed to own beneficially the shares held by IVMC.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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