Press Release

Seattle Genetics Prices Public Offering of Common Stock

BOTHELL, Wash., Feb 02, 2011 (BUSINESS WIRE) --

Seattle Genetics, Inc. (Nasdaq: SGEN) today announced the pricing of an underwritten public offering of 10,000,000 shares of its common stock, offered at a price to the public of $15.50 per share. The gross proceeds to Seattle Genetics from this offering are expected to be $155,000,000, before deducting underwriting discounts and commissions and other estimated offering expenses payable by Seattle Genetics. Seattle Genetics has granted the underwriters a 30-day option to purchase up to an aggregate of 1,500,000 additional shares of common stock to cover overallotments, if any. All of the shares in the offering are to be sold by Seattle Genetics. The offering is expected to close on or about February 7, 2011, subject to customary closing conditions.

Jefferies & Company, Inc. and J.P. Morgan Securities LLC are acting as joint book-running managers for the proposed offering. Leerink Swann LLC and RBC Capital Markets, LLC are acting as co-lead managers for the proposed offering. Needham & Company, LLC, William Blair & Company, LLC, Oppenheimer & Co. Inc. and ThinkEquity LLC are acting as co-managers for the proposed offering.

Seattle Genetics anticipates using the net proceeds from the offering to fund potential regulatory approval of brentuximab vedotin and continuing preparations for the potential commercial launch of brentuximab vedotin, to fund Seattle Genetics' research and development efforts, including clinical trials and manufacturing campaigns for its product candidates, and for working capital and general corporate purposes.

A shelf registration statement relating to the shares was filed with the Securities and Exchange Commission and is effective. A preliminary prospectus supplement related to the offering has been filed with the SEC and is available on the SEC's website located at www.sec.gov. Copies of the final prospectus supplement relating to these securities, when available, may be obtained from Equity Syndicate Prospectus Department, Jefferies & Company, Inc., 520 Madison Avenue, 12th Floor, New York, NY, 10022, at 877-547-6340, and at Prospectus_Department@Jefferies.com, or from J.P. Morgan Securities LLC, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, New York 11717 or by calling 1-866-803-9204.

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 other jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or other jurisdiction.

About Seattle Genetics

Seattle Genetics is a clinical-stage biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer and autoimmune diseases.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to Seattle Genetics' expectations regarding the completion and timing of the closing of the public offering and its anticipated use of net proceeds from the offering, as well as the potential commercial launch of brentuximab vedotin. 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, without limitation, risks and uncertainties related to market conditions and the satisfaction of customary closing conditions related to the public offering; the risk that the safety and/or efficacy results of our completed clinical trials of brentuximab vedotin will not support marketing approval for the submitted indications; and the risk that we may not obtain priority review of our marketing application and consequently may be delayed in the planned U.S. commercial launch of brentuximab vedotin if approved for commercial sale. In addition, there can be no assurance that Seattle Genetics will be able to complete the public offering on the anticipated terms, or at all. Seattle Genetics will continue to need significant amounts of additional capital to fund its operations and may be unable to raise capital when needed, which would force Seattle Genetics to delay, reduce the scope of or eliminate one or more of its development programs. Additional risks and uncertainties relating to the offering, Seattle Genetics and its business can be found under the heading "Risk Factors" in Seattle Genetics' Quarterly Report on Form 10-Q for the quarter ended September 30, 2010, and in the preliminary prospectus supplement related to the public offering filed with the Securities and Exchange Commission on February 1, 2011. 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.

SOURCE: Seattle Genetics, Inc.

Seattle Genetics, Inc.
Peggy Pinkston
425-527-4160
ppinkston@seagen.com