Exhibit 3.1

FIFTH AMENDED AND RESTATED

CERTIFICATE OF INCORPORATION

OF

TESARO, INC.

ARTICLE I

Name

The name of the corporation is TESARO, Inc. (the “Corporation”).

ARTICLE II

Registered Office and Registered Agent

The address of the registered office of the Corporation in the State of Delaware is 251 Little Falls Drive, Wilmington, New Castle County, Delaware 19808.  The name of the registered agent of the Corporation at such address is Corporation Service Company.

ARTICLE III

Corporate Purpose

The purpose of the Corporation is to engage in any lawful act or activity for which corporations may be organized under the General Corporation Law of Delaware (the “General Corporation Law”).

ARTICLE IV

Capital Stock

The total number of shares of all classes of stock that the Corporation shall have authority to issue is 1000, all of which shall be shares of Common Stock, par value $0.0001 per share.

ARTICLE V

Directors

(1)   Elections of directors of the Corporation need not be by written ballot, except and to the extent provided in the by-laws of the Corporation.

(2)   To the fullest extent permitted by the General Corporation Law of Delaware as it now exists and as it may hereafter be amended, no director of the Corporation shall be personally liable to the Corporation or its stockholders for monetary damages for breach of fiduciary duty as a director.

ARTICLE VI

Indemnification of Directors, Officers and Others

(1)   To the fullest extent permitted by applicable law, the Corporation is authorized to provide indemnification of (and advancement of expenses to) directors, officers and agents of the Corporation (and any other persons to which the General Corporation Law permits the Corporation to provide indemnification) through by-law provisions, agreements with such agents or other persons, vote of stockholders or disinterested directors, or otherwise, in excess of the indemnification and advancement otherwise permitted by Section 145 of the General Corporation Law, subject only to limits created by applicable provisions of the General Corporation Law (statutory or nonstatutory), with respect to actions for breach of duty to the Corporation and its stockholders.

(2)   Any amendment, repeal or modification of the foregoing provisions of this ARTICLE VI shall not adversely affect any right or protection of a director, officer, agent, or other person existing at the time of, or increase the liability of any director of the Corporation with respect to any acts or omissions of such director, officer or agent occurring prior to, such amendment, repeal or modification.

ARTICLE VII

By-laws

The directors of the Corporation shall have the power to adopt, amend or repeal by-laws.

ARTICLE VIII

Reorganization

Whenever a compromise or arrangement is proposed between this Corporation and its creditors or any class of them and/or between this Corporation and its stockholders or any class of them, any court of equitable jurisdiction within the State of Delaware may, on the application in a summary way of this Corporation or of any creditor or stockholder thereof or on the application of any receiver or receivers appointed for this Corporation under §291 of Title 8 of the Delaware Code or on the application of trustees in dissolution or of any receiver or receivers appointed for this Corporation under §279 of Title 8 of the Delaware Code order a meeting of the creditors or class of creditors, and/or of the stockholders or class of stockholders of this Corporation, as the case may be, to be summoned in such manner as the said court directs.  If a majority in number representing three fourths in value of the creditors or class of creditors, and/or of the stockholders or class of stockholders of this Corporation, as the case may be, agree

to any compromise or arrangement and to any reorganization of this Corporation as consequence of such compromise or arrangement, the said compromise or arrangement and the said reorganization shall, if sanctioned by the court to which the said application has been made, be binding on all the creditors or class of creditors, and/or on all the stockholders or class of stockholders, of this Corporation, as the case may be, and also on this Corporation.

ARTICLE IX

Amendment

The Corporation reserves the right to amend, alter, change or repeal any provision of this Certificate of Incorporation in the manner now or hereafter prescribed by law, and all the provisions of this Certificate of Incorporation and all rights conferred on stockholders, directors, officers and other persons in this Certificate of Incorporation are subject to this reserved power.