Seattle Genetics, Inc. (NASDAQ: SGEN) today announced the pricing of an underwritten public offering of 11,707,318 shares of its common stock at a price to the public of $41.00 per share. All of the shares are being sold by Seattle Genetics. The gross proceeds to Seattle Genetics from the offering, before deducting the underwriting discounts and commissions and other offering expenses, are expected to be approximately $480 million. The offering was upsized by 20 percent from the originally anticipated gross offering amount of $400 million. The offering is expected to close on or about September 16, 2015, subject to customary closing conditions. In addition, Seattle Genetics has granted the underwriters of the offering a 30-day option to purchase up to an additional 1,756,097 shares of its common stock at the public offering price, less the underwriting discounts and commissions, solely to cover overallotments.

Seattle Genetics anticipates using the net proceeds from the offering to fund the ongoing commercialization of ADCETRIS® (brentuximab vedotin) in the United States and Canada, to fund its research and development efforts designed to further expand the ADCETRIS label and to advance its pipeline of product candidates, as well as for general corporate purposes, including working capital.

J.P. Morgan Securities LLC is acting as lead book-running manager for the offering. Leerink Partners LLC is also acting as a book-running manager. UBS Securities LLC, Barclays Capital Inc., RBC Capital Markets, LLC, Needham & Company, LLC and William Blair & Company L.L.C. are acting as co-managers.

A shelf registration statement relating to the shares was filed with the Securities and Exchange Commission and became automatically effective on September 9, 2015. The offering is being made solely by means of a prospectus. A copy of the final prospectus supplement and accompanying prospectus relating to the offering, when available, may be obtained from J.P. Morgan Securities LLC, Attention: Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, or by telephone at (866) 803-9204, or by email at prospectus-eq_fi@jpmchase.com; or Leerink Partners LLC, Attention: Syndicate Department, One Federal Street, 37th Floor, Boston, MA 02110, or by telephone at (800) 808-7525 ext. 6142, or by email at syndicate@leerink.com.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these 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 Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development and commercialization of innovative antibody-based therapies for the treatment of cancer.

Forward-Looking Statements

Certain of the statements made in this press release are forward looking, such as those, among others, relating to Seattle Genetics’ expectations regarding the anticipated closing date and Seattle Genetics’ anticipated use of net proceeds from the offering. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include risks and uncertainties related to completion of the public offering on the terms to which the company has agreed or at all, market conditions and the satisfaction of customary closing conditions related to the public offering. More information about the risks and uncertainties faced by Seattle Genetics is contained in the section captioned “Risk factors” in the preliminary prospectus supplement related to the public offering filed with the Securities and Exchange Commission (the “SEC”) and in the final prospectus supplement related to the public offering to be filed with the SEC. Seattle Genetics disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.