Genzyme Files Applications for Approval of Mozobil in the United States and Europe

Genzyme Corporation (Nasdaq: GENZ) announced today that it has submitted marketing applications in both the United States and the European Union for Mozobil™ (plerixafor), a product candidate intended to enhance mobilization of hematopoietic stem cells for collection and subsequent autologous transplantation in patients with lymphoma and multiple myeloma. The company has requested priority review of its U.S. application and, if granted, Mozobil could be approved by the end of this year. European approval is expected in 2009. Additional global applications in up to 60 countries are expected to follow.

Important Clinical Role

Mozobil is designed to mobilize stem cells from the bone marrow into the bloodstream where they can be collected, making it more likely for a patient with certain types of cancers to receive a successful transplant. Specifically, patients with non-Hodgkin’s and Hodgkin’s lymphomas and multiple myeloma often receive high-dose chemotherapy, a process that destroys bone marrow. A stem cell transplant is required to replenish blood-forming bone marrow cells destroyed by high-dose chemotherapy. Stem cells differentiate into the mature red blood cells, white blood cells, and platelets that a healthy person needs.

Currently, before a transplant can take place, patients may receive a prescribed dose of chemotherapy and/or other drugs, called growth factors, to help mobilize their hematopoietic stem cells into the bloodstream. Once the cells are released into the bloodstream, they are easier to collect in preparation for a transplant.

In order for the transplant to take place, a minimum number of approximately 2 million cells per kilogram of body weight must be collected. For many patients, this process can take three or four hours over multiple days to complete. Even then, some patients are not able to mobilize enough cells, and a transplant is not possible.

Genzyme conducted two phase 3 studies that confirmed the potential of Mozobil to effectively and predictably prepare lymphoma and multiple myeloma patients for an autologous transplant. Both studies successfully met primary and secondary endpoints. Patients who received Mozobil in conjunction with a growth factor achieved more rapid and effective mobilization of stem cells in preparation for autologous transplant than patients treated with growth factor alone. In addition, more patients treated with Mozobil plus a growth factor achieved a composite endpoint of optimal stem cell collection and successful transplantation, compared to patients mobilized with placebo plus a growth factor. Mozobil was well tolerated in both trials, with the most common adverse events being gastrointestinal effects and injection site reactions.

“There is a lot of excitement among treating physicians about Mozobil,” said Mark Goldberg, M.D., senior vice president of clinical research at Genzyme. “The product has great potential to meet an important, unmet medical need and has numerous potential benefits for patients.”

More than 900 patients have received Mozobil through a compassionate use program in the United States, and similar compassionate use programs have recently begun in Europe.

Commercialization Plans

Genzyme plans to launch Mozobil in the U.S. and Europe in 2009. Upon commercial launch, Mozobil will be marketed and sold by Genzyme’s existing Transplant sales force, which has a commercial presence in more than 55 countries worldwide. In addition, the company will leverage its Oncology business and clinical infrastructure.

Approximately 55,000 stem cell transplants are performed each year for multiple myeloma, Hodgkin’s and non-Hodgkin’s lymphoma, and other conditions in markets where Genzyme has a commercial infrastructure, including the United States, Europe, Latin America and the Asian Pacific countries. Genzyme believes that over time, Mozobil will be used in the majority of these procedures, and peak sales of the product in the transplant setting are expected to reach $400 million annually.

In addition to the patient benefit, Mozobil also may offer significant economic benefits for transplant centers. Mozobil has the potential to decrease the number of apheresis days and provide transplant centers with more predictable and efficient use of the apheresis center, while reducing the number of patients who may fail to mobilize sufficient numbers of cells and therefore require a second mobilization procedure.

Additional Therapeutic Opportunities

Numerous Genzyme and investigator-sponsored trials are planned or underway to study Mozobil’s use in other settings such as allogeneic hematopoietic stem cell transplants. Genzyme is also studying the use of Mozobil to improve the efficacy of chemotherapy and/or immunotherapy in various types of hematologic malignancies such as chronic lymphocytic leukemia and acute myelogenous leukemia, and is pursuing preclinical work to explore the role that Mozobil may play in cord blood transplantation, solid organ transplantation, cardiovascular disease, renal ischemic disease, and a variety of additional types of solid tumor malignancies.

“We’re just beginning to unlock the potential of Mozobil,” said Joseph Lobacki, senior vice president of the Transplant business unit at Genzyme.

Genzyme® and AnorMED® are registered trademarks of Genzyme Corporation or its subsidiaries. Mozobil™ is an unregistered trademark of Genzyme Corporation or its subsidiaries. All rights reserved.

This press release contains forward-looking statements, including the statements regarding: the anticipated timing of product approvals in the U.S. and Europe, the anticipated timing of filing additional applications for approval in other countries, the potential adoption of Mozobil in the marketplace, the potential benefits to different types of patients, commercial launch plans and Mozobil’s potential use in other therapeutic applications. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those projected in these forward-looking statements. These risks and uncertainties include, among others, the failure to receive regulatory approval to commercialize Mozobil in the U.S., Europe or other countries, the lack of adoption of the product in other therapeutic areas, the inability to change current treatment protocols and risks associated with commercial launch and the risks and uncertainties described in reports filed by Genzyme with the Securities and Exchange Commission under the Securities Exchange Act of 1934, as amended, including without limitation the information under the heading “Risk Factors” in the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of the Genzyme Quarterly Report on Form 10-Q for the quarter ending March 31, 2008. Genzyme cautions investors not to place substantial reliance on the forward-looking statements contained in this press release. These statements speak only as of the date of this press release, and Genzyme undertakes no obligation to update or revise the statements.