New Data Demonstrate ZEVALIN(R) Radioimmunotherapy May Play Greater Role in Combination with Standard of Care for Various Types of Lymphoma.

ATLANTA -- Abstracts Presented at 2005 ASH Annual Meeting Reveal Benefits of Earlier Use of ZEVALIN, Including in Disease that is Hardest to Treat

Biogen Idec Inc. (Nasdaq:BIIB) announced that new data, presented today at the 47th Annual Meeting of the American Society of Hematology (ASH) in Atlanta, December 10-13, demonstrate that patients may benefit from earlier and consolidated use of ZEVALIN(R) (Ibritumomab Tiuxetan) radioimmunotherapy in refractory and hard-to-treat cancers, including diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma (MCL), and follicular non-Hodgkin's lymphoma (FL).

"The ZEVALIN data released at this year's ASH meeting indicate the importance of ZEVALIN to research and the future of cancer treatment," said Arturo Molina, M.D., senior director, Medical Research Oncology/Hematology for Biogen Idec. "What's particularly intriguing about these data is that they demonstrate how therapies such as ZEVALIN may be integrated into the current standard of care for a variety of lymphomas. Just as researchers in HIV look to 'cocktails' of therapies to better manage patient disease, we are continually looking at how we can integrate radioimmunotherapy in the oncology arena to give patients additional options and extend survival."

ZEVALIN Plus a Standard Treatment Regimen May Help Prevent Relapse in DLBCL

Paul A. Hamlin, M.D., of Memorial Sloan-Kettering Cancer Center, delivered a poster presentation discussing a Phase II study that is exploring the feasibility and effectiveness of first line use of ZEVALIN and standard rituximab plus CHOP (R-CHOP) chemotherapy in older patients with high risk diffused large B-cell lymphoma (DLBCL), a disease that represents approximately one-third of all lymphomas and primarily impacts people over 60 years of age.

Patients received R-CHOP chemotherapy at standard doses for induction therapy. After hematologic recovery and R-CHOP restaging, patients were eligible for ZEVALIN, which was given 6-9 weeks post R-CHOP.

No patients receiving the full treatment regimen of ZEVALIN and R-CHOP in this study relapsed, with 21-month median follow-up. In addition, sequential R-CHOP followed by ZEVALIN was associated with manageable toxicities. As part of a unique collaborative effort, The University of Texas M.D. Anderson Cancer Center has joined Memorial Sloan Kettering Cancer Center in accruing additional patients for this study.

"We continue to learn more about the benefits of systemic radioimmunotherapy in a variety of lymphomas and we have not yet reached the limits of this therapy's capabilities," said Paul A. Hamlin, M.D., Memorial Sloan-Kettering Cancer Center. "The results of this study are particularly encouraging given the growing number of patients with high risk DLBCL who are under-served by current therapies."

ZEVALIN Consolidation as Part of an Abbreviated Chemotherapy Regimen

Nicholas A. DeMonaco, M.D., of the University of Pittsburgh, delivered a poster presentation describing a Phase II study designed to evaluate the safety and efficacy of abbreviated CHOP-rituximab (CHOP-R) followed by ZEVALIN and rituximab in patients with previously-untreated follicular non-Hodgkin's lymphoma.

In this study, eligible patients are given CHOP-R in standard doses. Four weeks after the last dose, patients receive the ZEVALIN therapeutic regimen, followed by four doses of rituximab one week later.

At the planned interim analysis after accrual of 19 patients, 8 patients had completed therapy and follow-up studies. The overall response rate after three cycles of CHOP-R was 75% with a complete response in two of the eight patients (25%). After treatment with ZEVALIN and rituximab, seven of eight patients achieved a complete response (87.5%).

ZEVALIN May Help Reduce Relapse in High Risk Mantle Cell Lymphoma

Amrita Krishnan, M.D., of the City of Hope National Cancer Center, delivered an oral presentation discussing the benefits of a new transplant strategy involving ZEVALIN to reduce relapse in high risk mantle cell lymphoma, a disease for which there are typically no long-term survivors. High dose chemotherapy (HDC) with autologous stem cell transplantation (ASCT) has been used for some of these patients, however, relapse rates remain high. This trial was designed to investigate the efficacy of combining ZEVALIN with HDC and ASCT to reduce relapse rates in patients with high-risk MCL.

Eighteen patients with MCL were enrolled in one of two ZEVALIN ASCT trials. The first was a phase I/II dose escalation trial of high-dose ZEVALIN plus cyclophosphamide and etoposide. The second study was a phase I/II trial of standard dose ZEVALIN and BEAM (BCNU, cytarabine, etoposide, melphalan).

No patients administered ZEVALIN as part of this study experienced relapse in the first 12 months. With a median follow up of 19 months, the estimated overall survival and disease free survival at two years for patients with high-risk mantle cell lymphoma enrolled in the study and treated with ZEVALIN is 79% and 59% respectively.

ZEVALIN May Provide an Effective Treatment Option for Relapsed and Refractory MCL

Anas Younes, M.D., of the UT M.D. Anderson Cancer Center, delivered a poster presentation discussing results from an ongoing phase II study designed to evaluate the efficacy and safety of ZEVALIN for patients with relapsed and refractory mantle cell lymphoma (MCL).

Twenty-two patients were enrolled in the study. All patients had been previously treated with rituximab with or without other chemotherapy. The median number of prior regimens was three.

Objective responses were observed in eight of 22 patients (36%), including three complete responses (23%).

"Although the duration of responses has been short, the potential for ZEVALIN to prolong the lives of heavily pretreated MCL patients seems promising," said Younes. "We believe that further investigation into the efficacy of ZEVALIN in these patients, particularly as front-line therapy or after first relapse, is warranted."

ZEVALIN Safety Profile

Rare deaths have occurred within 24 hours of rituximab infusions. These fatalities were associated with an infusion reaction symptom complex that included hypoxia, pulmonary infiltrates, acute respiratory distress syndrome, myocardial infarction, ventricular fibrillation, or cardiogenic shock. Yttrium-90 ZEVALIN administration results in severe and prolonged cytopenias in most patients. Patients experiencing severe cutaneous and mucocutaneous reactions should not receive any further components of the ZEVALIN therapeutic regimen and should seek prompt medical evaluation.

In safety data based upon 349 patients, the most serious adverse reactions of the ZEVALIN therapeutic regimen were primarily hematologic, with grade 4 neutropenia, thrombocytopenia, and anemia occurring in 30%, 10% and 3% of patients treated at the 0.4 mCi/kg dose, respectively. Infusion-related toxicities were typically grade 1 or 2 and were associated with pre-administration of rituximab (RITUXAN). The risk of hematologic toxicity correlated with the degree of bone marrow involvement prior to ZEVALIN therapy. Seven percent of patients were hospitalized with infection (3% of these had neutropenia) and fatal cerebral hemorrhage (less than 1%) has occurred in a minority of patients in clinical studies. Myelodysplasia or acute myelogenous leukemia was observed in 1% of patients (8 to 34 months after treatment).

ZEVALIN should only be used by health care professionals qualified by training and experience in the safe use of radionuclides.

About ZEVALIN

On February 19, 2002, the ZEVALIN therapeutic regimen became the first radioimmunotherapy approved by the U.S. Food and Drug Administration (FDA). Radioimmunotherapy is an innovative form of cancer treatment that offers an option to patients with certain types of B-cell non-Hodgkin's lymphoma who have failed to adequately respond to other cancer therapies. ZEVALIN is FDA-approved for the treatment of patients with relapsed or refractory low grade, follicular or transformed B cell non Hodgkin's lymphoma, including patients with rituximab (RITUXAN) refractory follicular non-Hodgkin's lymphoma. Determination of the effectiveness of ZEVALIN in a relapsed or refractory patient population is based on overall response rates. The effects of ZEVALIN on survival are not known.

The ZEVALIN therapeutic regimen combines a monoclonal antibody with a radioisotope. The monoclonal antibody in ZEVALIN recognizes and attaches to a particular cell-surface protein on B-cells called the CD20 antigen. This allows ZEVALIN to specifically target B-cells, destroying malignant NHL B-cells and also normal B-cells. The generic name for ZEVALIN is ibritumomab tiuxetan.

Today, ZEVALIN is being investigated in a variety of lymphoma subtypes including aggressive disease. ZEVALIN is also being studied in a number of different treatment strategies including combinations with front-line and salvage chemotherapy regimens and as part of autologous and allogeneic stem cell transplantation in both indolent and aggressive lymphoma subtypes.

About Biogen Idec

Biogen Idec creates new standards of care in oncology, neurology and immunology. As a global leader in the development, manufacturing, and commercialization of novel therapies, Biogen Idec transforms scientific discoveries into advances in human healthcare. For ZEVALIN product labeling, press releases and additional information about the company, please visit http://www.biogenidec.com.

Biogen Idec Safe Harbor

This press release contains forward-looking statements regarding ZEVALIN as a treatment for various indications. These statements are based on the companies' current beliefs and expectation. Drug development involves a high degree of risk. Factors which could cause actual results to differ materially from the companies' current expectations include: the risk that unexpected concerns may arise from additional data or analysis, that regulatory authorities may require additional information, further studies, or may fail to approve the drug, or that the company may encounter other unexpected hurdles. For more detailed information on the risks and uncertainties associated with Biogen Idec's drug development and other activities, see the periodic reports of Biogen Idec Inc. filed with the Securities and Exchange Commission. Biogen Idec assumes no obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise.