FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES 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 *   INTERWEST PARTNERS X LP 2. Date of Event Requiring Statement (Month/Day/Year) 06/27/2012 3. Issuer Name and Ticker or Trading Symbol TESARO, Inc. [TSRO] (Last) (First) (Middle) 2710 SAND HILL ROAD, SUITE 200 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) MENLO PARK, CA 94025 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series B Preferred Stock	  (1)	  (1)	Common Stock	2,627,257	$ (1)	D (2)	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
INTERWEST PARTNERS X LP 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
CASH HARVEY B 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
CLEVELAND BRUCE A 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
Ehrlich Christopher B 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
GIANOS PHILIP T 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
Kjellson Nina S 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
Kliman Gilbert H 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
Pepper Douglas A 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â
Holmes W Stephen 2710 SAND HILL ROAD, SUITE 200 MENLO PARK, CA 94025	Â	  X	Â	Â

Signatures

/s/ W. Stephen Holmes, Managing Director		06/27/2012
**Signature of Reporting Person		Date
/s/ Harvey B. Cash by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ Bruce A. Cleveland by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ Christopher B. Ehrlich by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ Philip T. Gianos by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ W. Stephen Holmes		06/27/2012
**Signature of Reporting Person		Date
/s/ Nina Kjellson by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ Gilbert H. Kliman by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date
/s/ Douglas A. Pepper by Karen A. Wilson Power of Attorney		06/27/2012
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(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).
(1)	The reported securities are convertible at any time, in whole or in part, at the option of the holder, have no expiration date, and will convert into shares of common stock immediately prior to the closing of the Issuer's initial public offering.
(2)	The shares are owned by InterWest Partners X, LP ("IW10"). InterWest Management Partners X, LLC ("IMP10") is the general partner of IW10. Harvey B. Cash, Bruce A. Cleveland, Christopher B. Ehrlich, Philip T. Gianos, W. Stephen Holmes, Nina S. Kjellson, Gilbert H. Kliman, Arnold L. Oronsky, Douglas A. Pepper and Thomas L. Rosch are managing directors of IMP10. Keval Desai and Khaled A. Nasr are venture members of IMP10. Each managing director and venture member of IMP10 disclaims beneficial ownership of such shares, except to the extent of their pecuniary interest therein.
  Remarks: Due to limitations of the EDGAR software, this Form 3 is filed on behalf of InterWest Partners X, LP and certain other Reporting Persons, and is being filed on two Forms 3 (Part I and Part II) (collectively, the ''InterWest Form 3'').  This filing represents Part I of the InterWest Form 3 and should be read together with Part II. Part I and Part II of the InterWest Form 3 shall constitute one filing. Exhibit List Exhibit 24.1- Power of Attorney of Harvey B. Cash Exhibit 24.2- Power of Attorney of Bruce A. Cleveland Exhibit 24.3- Power of Attorney of Christopher B. Ehrlich Exhibit 24.4- Power of Attorney of Philip T. Gianos Exhibit 24.5- Power of Attorney of Nina Kjellson Exhibit 24.6- Power of Attorney of Gilbert H. Kliman Exhibit 24.7- Power of Attorney of Douglas A. Pepper Exhibit 99 - Form 3 Joint Filer Information

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