Phase I/II Data Support Continued Development of Biogen Idec's Novel Anti-CD23 Antibody for Chronic Lymphocytic Leukemia.

Lumiliximab in Combination with Common Therapy Shows Potential to Improve Complete Response Rates in Patients with Progressive Disease

ORLANDO, Fla. -- Biogen Idec (Nasdaq: BIIB) announced data from a Phase I/II study of an investigational anti-CD23 monoclonal antibody, lumiliximab, suggesting it may be synergistic with fludarabine, cyclophosphamide and rituximab (FCR), an emerging standard of care for chronic lymphocytic leukemia (CLL) patients. When added to the FCR regimen, lumiliximab demonstrated a 52 percent complete response (CR) rate in patients who have CLL that was progressing after prior therapy. The data were announced at the 48th Annual Meeting of the American Society of Hematology (ASH), being held December 9-12 in Orlando.

In the lumiliximab study of 31 patients, lumiliximab added to the FCR regimen achieved a 52 percent CR. CR rate is a predictor of progression-free survival in CLL patients. Based on the positive results of the trial, Biogen Idec is initiating a registrational global, multicenter clinical trial comparing lumiliximab plus FCR vs. FCR alone.

"The CD23 antibody is a promising therapeutic approach for this disease because the antigen is highly expressed on B-CLL cells," said John C. Byrd, M.D., D. Warren Brown professor of Leukemia Research, director, Hematologic Malignancies Program, The Arthur James Comprehensive Cancer Center, The Ohio State University. "The results from this study - including a 52 percent complete response rate - support our hypothesis that lumiliximab may operate in synergy with the FCR regimen to improve clinical outcomes. This new targeted therapy may help us improve upon therapeutic options for CLL patients."

The ASH meeting is the first time a complete response data set has been presented on this investigational novel anti-CD23 monoclonal antibody, which may be a first in class therapy. Biogen Idec owns the full worldwide rights to lumiliximab.

Thirty-one patients with relapsed CLL enrolled in this study of lumiliximab in combination with FCR. An overall response rate of 71 percent was demonstrated: 52 percent CR, 10 percent partial response (PR), and 13 percent unconfirmed PR. Response was generally achieved after three to five cycles of therapy. In this study, lumiliximab in combination with FCR appears to be well tolerated as compared to what would be expected from FCR alone.

"The lumiliximab results support the initiation of a randomized, registrational study in CLL. We continue to support our strong pipeline in hematologic malignancies and solid tumors," said David Parkinson, M.D., senior vice president, Oncology Research and Development, Biogen Idec. "At Biogen Idec, we are dedicated to creating new and novel approaches to cancer treatment that can make a significant difference in patients' lives."

About the Study

The study is an open-label, dose-escalation, multi-center Phase I/II study (Study 152-30). Patients 18 years of age or older with relapsed CD23+ B-cell CLL were eligible. Patients enrolled had progressive, symptomatic CLL as defined by National Cancer Institute (NCI) criteria, a median age of 58, and had undergone a median of two prior treatments (range, 1 to 9).

The FCR treatment regimen was used in this trial because it has been established as the emerging standard of care for CLL patients. A study conducted at The MD Anderson Cancer Center demonstrated that the FCR regimen was an active and well-tolerated treatment for previously treated patients with CLL, and achieved a complete response rate (CR) of 25 percent (Weirda et al, Journal of Clinical Oncology, Vol 23, No 18 (June 20), 2005: pp. 4070-4078).

In the study, 31 patients received either 375 mg/m2 (n=3) or 500 mg/m2 (n=28) of lumiliximab in combination with a 28-day cycle of FCR for up to 6 cycles. Currently, baseline cytogenetic data is available for 21 patients who received 500 mg/m2 of lumiliximab. The majority of patients (74 percent) were Rai Stage I/II. Twenty patients experienced a Grade 3 or 4 adverse event, (all of which were hematologic toxicities commonly associated with the FCR regimen). The most common study-related adverse events included nausea (77 percent), pyrexia (61 percent), chills (55 percent), neutropenia (55 percent) and fatigue (48 percent). Response was evaluated at weeks 13 and 25 using the National Cancer Institute Working Group (NCI-WG) criteria.

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 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 the development of lumiliximab and its potential 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 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.