Results of Four ZEVALIN Clinical Studies Presented At ASH.

NEW ORLEANS--(BW HealthWire)--Dec. 6, 1999--

IDEC Pharmaceuticals Corporation (Nasdaq:IDPH) today announced that preliminary results of four clinical trials of ZEVALIN(TM) (ibritumomab tiuxetan, IDEC-Y2B8), an investigational radioimmunotherapy, will be presented at the 41st Annual Meeting of the American Society of Hematology (ASH).

ZEVALIN is a monoclonal antibody that targets the CD20 antigen and is stably linked to the radioisotope 90Yttrium. This investigational agent is in late stages of development for the treatment of certain non-Hodgkin's lymphomas (NHL).

"The interim ZEVALIN clinical response and safety data included in these presentations are encouraging," said Christine A. White, M.D., IDEC Pharmaceuticals' senior director of oncology and hematology and an author in all four presentations. "In addition, these preliminary data indicate that ZEVALIN can be dosed based on clinical factors including patient body weight and baseline platelet count without need for complex and time-consuming dosimetry. Final conclusions, of course, await completion of these studies."

ZEVALIN Plus Rituxan(R) (Rituximab) vs. Rituxan Alone

Thomas E. Witzig, M.D. of the Mayo Clinic, Rochester, MN, delivered an oral presentation of Phase III interim results comparing ZEVALIN, plus Rituxan, to Rituxan alone in patients with relapsed or refractory, low grade, follicular or transformed CD20-positive, B-cell NHL.

He reported that the prospectively defined 90-patient interim analysis of the multi-center, randomized controlled study showed an overall response rate (ORR) of 80 percent for the ZEVALIN group compared to ORR of 44 percent for the Rituxan group. A treatment course for ZEVALIN includes a Rituxan infusion (250 mg/m2) on day one, followed by infusions of Rituxan (250 mg/m2) and ZEVALIN (at a standard radiation dose of 0.4 mCi/kg of patient body weight) on day eight. Patients in the Rituxan arm received four infusions of Rituxan (at the indicated dose of 375 mg/m2) once a week over 22 days.

Dr. Witzig also stated that 21 percent of the ZEVALIN group achieved a complete response to therapy and 59 percent achieved a partial response. ZEVALIN associated toxicity was primarily hematologic, transient and reversible. Six percent of patients in the ZEVALIN arm of the study experienced Grade 4 thrombocytopenia (platelet count below 10,000/mm3) and 25 percent experienced Grade 4 neutropenia (neutrophil count below 500/mm3). However, patients recovered in a median of 12 and 14 days, respectively. The overall safety profile for treatment with Rituxan in the study was similar to what has been outlined in the Rituxan package insert.

ZEVALIN for Relapsed or Refractory NHL Patients with Mild Thrombocytopenia

Dr. Witzig also gave a poster presentation of interim results of a Phase II trial evaluating safety and efficacy of treating relapsed or refractory, low grade, follicular or transformed NHL patients with mild thrombocytopenia (platelet count between 100,000 and 149,000/mm3) with ZEVALIN at a reduced radiation dose (0.3 mCi/kg).

The overall response rate in 22 evaluable patients was 68 percent with five patients (23 percent) achieving a complete response and 10 patients (45 percent) achieving a partial response.

In the study, 25 percent of patients experienced Grade 4 neutropenia and 15 percent experienced Grade 4 thrombocytopenia. Again, the toxicity of ZEVALIN was primarily hematologic, transient and reversible with patients recovering in a median of 12 and 14 days, respectively.

ZEVALIN in NHL Patients Previously Treated with Rituxan

Leo I. Gordon, M.D. of the Robert H. Lurie Cancer Center, Northwestern University, Chicago, IL, authored a poster presentation of interim results of a non-randomized controlled, open-label Phase III trial evaluating the safety and efficacy of ZEVALIN in follicular NHL patients who are refractory to Rituxan, i.e., who did not achieve a response or had a time to progression (TTP) of less than six months with the most recent course of Rituxan.

The interim overall response rate was 46 percent with all responders achieving a partial response. Eighty percent of these patients had sizeable tumors (greater than 5cm in single diameter) and 76 percent were chemotherapy-resistant.

In a related poster presentation Gregory A. Wiseman, M.D. of the Mayo Clinic, Rochester, MN, summarized the dosimetry results obtained in the above study. He concluded that the ZEVALIN biodistribution and estimated radiation absorbed dose to normal body organs were not affected by prior treatment with Rituxan given two to 23 months earlier.

IDEC Pharmaceuticals focuses on the commercialization and development of targeted therapies for the treatment of cancer and autoimmune diseases. IDEC's antibody products act chiefly through immune system mechanisms, exerting their effect by binding to specific, readily targeted immune cells in the patient's blood or lymphatic systems.

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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. In addition to the matters described in this press release, achievement of product development milestone events and future product sales, the timing and success, and cost of product launches and clinical studies, and the level of manufacturing performance may result in period to period fluctuations in IDEC's revenues and earnings. In addition to these matters, 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, 1998 and Form 10-Q for the quarter ended September 30, 1999, may affect the actual results achieved by IDEC.

IDEC Pharmaceuticals and Rituxan are registered U.S. trademarks of the company. IDEC's headquarters is located at 11011 Torreyana Road, San Diego, CA 92121.