Data Show Improved Response Rate When Zevalin Plus Rituximab Follows Short Course First-Line Treatment in Patients with Follicular Lymphoma

Biogen Idec (NASDAQ: BIIB) announced today that data presented at
the 43rd American Society of Clinical Oncology (ASCO) annual meeting
showed that adding Zevalin(R) (Ibritumomab tiuxetan)
radioimmunotherapy to a short course first-line treatment followed by
rituximab weekly for four weeks doubled the rate of complete response
in patients with follicular lymphoma, from 44 percent with a standard
treatment regimen to 88 percent. Additionally, the response rate
(complete and partial responses) for patients in the study was 100
percent based on PET scan assessment.

"The increase in complete response rates when adding ZEVALIN
radioimmunotherapy is promising," said Samuel A. Jacobs, M.D.,
associate director for clinical investigations at the University of
Pittsburgh Cancer Institute and UPMC Cancer Centers. "These data add
to the growing body of evidence that using radioimmunotherapy as part
of front-line treatment may increase complete response rates."

About The Trial

In this Phase II study, patients with symptomatic, stages II-IV
and grades 1-3, untreated follicular lymphoma received three cycles of
R-CHOP, a standard treatment regimen, followed by ZEVALIN. One week
after ZEVALIN treatment, patients received rituximab weekly for four
weeks. The primary endpoint of the trial was complete response rate,
which was determined by CT scan, the conventional methodology, and PET
scan. Of 56 evaluable patients, 50 completed both phases of therapy
and were evaluated for response.

Results evaluated by CT scan showed that 44 percent of patients
had a complete response following the R-CHOP phase of treatment. After
treatment with ZEVALIN and extended dose rituximab, complete response
rate increased to 88 percent. Results evaluated by PET scan, a newer
method of evaluation, showed a complete response rate of 68 percent
with R-CHOP and 96 percent after treatment with ZEVALIN and extended
dose rituximab. The response rate in patients who completed the
treatment regimen was 100 percent based on PET scan assessment. Median
time to progression has not yet been reached; to date, five patients
have experienced disease progression. Adverse events included
myelosuppression and there was one episode of febrile neutropenia
after ZEVALIN and rituximab treatment.

"We believe that ZEVALIN may play an important role in the
treatment of lymphoma in the front-line setting and are encouraged
that data continues to underscore the impact that radioimmunotherapy
can have," said David Parkinson, M.D., senior vice president, Oncology
Research and Development, Biogen Idec. "In order to further understand
the potential of ZEVALIN as a first-line treatment, we have recently
initiated a phase III trial that will evaluate ZEVALIN as part of
first-line treatment with CVP, a commonly-used chemotherapy regimen."

ZEVALIN Safety Profile

Rare deaths have occurred within 24 hours of rituximab (RITUXAN)
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 3/4
neutropenia, thrombocytopenia, and anemia occurring in 60 percent, 63
percent and 17 percent respectively. Infusion-related toxicities were
typically grade 1 or 2 and were associated with pre-administration of
rituximab. The risk of hematologic toxicity correlated with the degree
of bone marrow involvement prior to ZEVALIN therapy. Myelodysplastic
syndrome (MDS) and/or acute myelogenous leukemia (AML) were reported
in 5.2% (11/211) of patients enrolled in clinical studies and 1.5%
(8/535) of patients included in the expanded-access trial, with median
follow-up of 6.5 and 4.4 years, respectively. 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 (Ibritumomab tiuxetan)
therapeutic regimen was approved by the U.S. Food and Drug
Administration (FDA) for the treatment of patients with relapsed or
refractory low grade, follicular or transformed B-cell non Hodgkin's
lymphoma (NHL), 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. Radioimmunotherapy 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.

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.

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 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.