IDEC Pharmaceuticals Obtains Summary Judgment in Patent Litigation against Corixa and GlaxoSmithKline

IDEC Pharmaceuticals Corporation (Nasdaq:IDPH) today announced that it has been granted summary judgment in its favor by the United States District Court for the Southern District of California. The Order, signed by a United States District Judge, finds that the four patents asserted by defendants Corixa Corporation, Coulter Corporation, the Regents of the University of Michigan and GlaxoSmithKline against IDEC’s Zevalin(R) Therapy Regimen are unenforceable due to the inventors’ inequitable conduct in the prosecution of the underlying patent applications.

The litigation was commenced on September 10, 2001, when IDEC filed a complaint against Corixa Corporation, Coulter Pharmaceutical, Inc., and the Regents of the University of Michigan, in federal court for the Southern District of California. The IDEC complaint sought a declaratory judgment that Zevalin(R) does not infringe patents held by the defendants or, in the alternative, that such patents were invalid. On September 12, 2001, Corixa, Coulter and GlaxoSmithKline filed a lawsuit against IDEC in federal court in the District of Delaware alleging that Zevalin infringes the same patents. This action was transferred to the federal court for the Southern District of California and was consolidated with the IDEC lawsuit.

Commenting on the development, William R. Rohn, President of IDEC, stated, “We are gratified that the Court agreed with our position in these consolidated cases. While there may be further procedural twists and turns and other litigation remains between the two sides, the Court’s Order is compelling in its finding of unenforceability of Corixa’s patents.”

General Information

IDEC Pharmaceuticals Corporation is a leader in the discovery, development, and commercialization of targeted immunotherapies for the treatment of cancer and autoimmune diseases. IDEC discovered and developed the first commercially available radioimmunotherapy product (Zevalin) approved in the United States, which is used to treat certain non-Hodgkin’s lymphomas. IDEC also discovered and, with co-promotion partner Genentech, Inc., developed the first monoclonal antibody product (Rituxan(R)) approved in the United States for the treatment of cancer. Rituxan is approved in over 70 countries worldwide and is also used to treat various types of non-Hodgkin’s lymphomas. IDEC is a San Diego based, integrated biopharmaceutical company with multiple products in clinical stage development and strategic alliances in a variety of research platforms.

For a menu of IDEC’s current news releases and quarterly reports or to retrieve a specific release, call (888) 329-2309. On the Internet check the News Center at IDEC’s website:

The statements made in this press release contain certain forward-looking statements that involve a number of risks and uncertainties. Actual events or results may differ from IDEC’s expectations. For example, the risk factors listed from time to time in IDEC’s SEC filings including but not limited to its Annual Report on Form 10-K for the year ended December 31, 2002 and its Quarterly Report on Form 10-Q for the three months ended June 30, 2003, may affect the actual results achieved by IDEC. These forward-looking statements represent the company’s judgment as of the date of this release. The company disclaims, however, any intent or obligation to update these forward-looking statements.

IDEC Pharmaceuticals, Rituxan and Zevalin are registered U.S. trademarks of the IDEC Pharmaceuticals Corporation. IDEC’s headquarters are located at 3030 Callan Road, San Diego, CA 92121.

CONTACT: IDEC Pharmaceuticals Corporation John M. Dunn, 858-431-8242 Vince Reardon, 858-431-8656 SOURCE: IDEC Pharmaceuticals Corporation