Exhibit A

JOINT FILING STATEMENT

I, the undersigned, hereby express my agreement that the attached Schedule 13D/A (and any amendments thereto) relating to the Common Stock of Tesaro, Inc. is filed on behalf of each of the undersigned.

Date: February 19, 2016

INTERWEST PARTNERS X, L.P.

By:	InterWest Management Partners X, LLC
Its:	General Partner
By:	/s/ Gilbert H. Kliman
	GILBERT H. KLIMAN
	Managing Director
INTERWEST MANAGEMENT PARTNERS X, LLC
By:	/s/ Gilbert H. Kliman
	GILBERT H. KLIMAN
	Managing Director
INTERWEST VENTURE MANAGEMENT COMPANY
By:	/s/ Gilbert H. Kliman
	Title: Secretary

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Philip T. Gianos

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Stephen Holmes III

/s/ Gilbert H. Kliman

Gilbert H. Kliman

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Arnold L. Oronsky

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Bruce A. Cleveland

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Khaled A. Nasr

/s/ Karen A. Wilson

Karen A. Wilson, Attorney-in-Fact for Keval Desai