Exhibit 99.1

Clovis Oncology Announces Exercise in Full by Initial Purchasers of

Their Option to Purchase an Additional $37.5 Million Aggregate

Principal Amount of its 2.50% Convertible Senior Notes due 2021

Boulder, CO, September 9, 2014 – Clovis Oncology, Inc. (NASDAQ: CLVS) announced today that the initial purchasers of the previously announced offering of the Company’s 2.50% Convertible Senior Notes due 2021 (the “Notes”) in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended, have elected to exercise in full their option to purchase an additional $37.5 million aggregate principal amount of the Notes. With the exercise of the option, a total of $287.5 million aggregate principal amount of the Notes will be sold at the closing of the offering, which is expected to occur on September 9, 2014, subject to customary closing conditions.

Clovis intends to use the net proceeds of this offering for general corporate purposes, including funding of its development programs, payment of milestones pursuant to its license agreements, general and administrative expenses, acquisition or licensing of additional product candidates or businesses and working capital.

This press release does not constitute an offer to sell or the solicitation of an offer to buy the notes or any other securities, nor will there be any sale of notes or any other securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

The notes and the shares of common stock issuable upon conversion of the notes have not been registered under the Securities Act or any state securities laws and, unless so registered, may not be offered or sold in the United States except pursuant to an applicable exemption from the registration requirements of the Securities Act and applicable state securities laws. This press release does not constitute an offer to sell or the solicitation of an offer to buy the notes or any other securities, nor will there be any sale of notes or any other securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Clovis Oncology

Clovis Oncology, Inc. is a biopharmaceutical company focused on acquiring, developing and commercializing innovative anti-cancer agents in the U.S., Europe and additional international markets. Clovis Oncology targets development programs at specific

subsets of cancer populations, and simultaneously develops diagnostic tools that direct a compound in development to the population that is most likely to benefit from its use. Clovis Oncology is headquartered in Boulder, Colorado.

Cautionary Note Regarding Forward-Looking Statements

To the extent that statements contained in this press release are not descriptions of historical facts regarding Clovis Oncology, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements involve substantial risks and uncertainties that could cause Clovis Oncology’s actual results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, the conditions affecting the capital markets, general economic, industry, or political conditions, and the satisfaction of customary closing conditions related to the proposed offering. Clovis Oncology undertakes no obligation to update or revise any forward-looking statements. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to the business of the company in general, see Clovis Oncology’s Annual Report on Form 10-K for the year ended December 31, 2013 and its other reports filed with the Securities and Exchange Commission.

# # #

- 2 -