Genzyme Granted Label Change for Thyrogen

Adds Improved Outcomes Data Demonstrating Patient Benefit.

February 1, 2006, Genzyme Corp. (Nasdaq:GENZ) today announced that the U.S. Food and Drug Administration (FDA) has authorized a label modification for Thyrogen® (thyrotropin alfa for injection) to reflect positive patient outcomes based on a new analysis of the pivotal study data that formed the basis of the product’s regulatory filing and approval in 1998.

Thyrogen is currently indicated in the U.S. for use as a diagnostic tool in the management of patients being tested for the recurrence of well-differentiated thyroid cancer. The product allows patients to avoid the potentially debilitating symptoms associated with thyroid hormone withdrawal.

The SF-36 Health Survey is a standardized instrument assessing a patient’s quality of life across eight domains, measuring both physical and mental functioning. A recent re-analysis of the SF-36 data from the pivotal trial of Thyrogen revealed that the quality of life data are shown to be in favor of the Thyrogen-treated arm in all eight domains (p‹0.0001 for all) compared to the withdrawal arm of the study. These domains include physical and social functioning, bodily pain, vitality and mental health. When the original regulatory filing for Thyrogen occurred, there was an error in the use of the measurement tool’s scoring algorithm. As a result, the quality of life data for the Thyrogen arm were shown to be statistically significant in favor of Thyrogen in only four of the eight domains. The label modification for Thyrogen now clearly states the positive impact of the product in all eight quality of life indicators.

“Changing the label is significant because it now underscores with quantitative data what has been seen in practice for the past several years - that Thyrogen has a positive impact on both physical and mental functioning of thyroid cancer patients,” stated Mike Heslop, senior vice president and general manager of Genzyme’s endocrine business. “The new label details the benefit that Thyrogen provides patients in alleviating hardships associated with withdrawal from thyroid hormone. As a result, it is our hope that more patients will pursue ongoing monitoring so that any recurrence of disease can be discovered and treated quickly.”

The new SF-36 quality of life data submitted to FDA for the label correction also serves as the basis of a forthcoming article to be published in the March edition of the Journal of Clinical Endocrinology and Metabolism, a leading, peer-reviewed journal for the field.

Recent data released from the U.S. National Cancer Institute shows that thyroid cancer is now ranked first among all cancers in incidence growth in both women and men. Additionally, for those patients that received successful initial treatment, recurrence rates of up to 30 percent underscore the importance of long-term, follow-up testing to foster early detection for what is considered a highly-treatable disease.

The American Cancer Society estimates that about 25,690 new cases of thyroid cancer were diagnosed in the United States last year. It is three times more common in women than in men. Most cases of thyroid cancer are discovered during a routine physical examination when a painless lump is found in the thyroid. In accordance with major guidelines for treating thyroid cancer, the majority of patients have their thyroid surgically removed and undergo radioiodine ablation which, in addition to facilitating follow-up monitoring, may reduce recurrences of thyroid cancer.

Background Information on Thyrogen

Thyrogen was initially approved for marketing in the United States in November, 1998 for use in patients with well-differentiated thyroid cancer who have had their thyroid gland removed as an adjunctive diagnostic tool for serum thyroglobulin (Tg) testing with or without radioiodine imaging. These patients must take thyroid hormone suppression therapy (THST) and undergo periodic testing to facilitate the early detection of recurrent disease. Thyrogen allows patients to remain on their THST and avoid the debilitating symptoms of clinical hypothyroidism during TSH stimulated follow-up testing. For patients who may be undergoing follow-up testing with a serum thyroglobulin test without being withdrawn from their thyroid hormone suppression therapy, Thyrogen offers significantly improved sensitivity for detection of recurrent or metastatic cancer. Thyrogen has been on the market in Europe since 2001 and in the U.S. since 1998.

Thyrogen is injected in a muscle, and is available only by prescription. The most common side effects reported in clinical studies were nausea, headache, weakness & vomiting. When using Thyrogen, there is a risk that thyroid cancer cells may not be detected and diagnosis of recurring cancer may be missed.

About Genzyme

One of the world’s leading biotechnology companies, Genzyme is dedicated to making a major positive impact on the lives of people with serious diseases. This year marks the 25th anniversary of Genzyme’s founding. Since 1981, the company has grown from a small start-up to a diversified enterprise with more than 8,000 employees in locations spanning the globe and 2005 revenues of $2.7 billion. Genzyme has been selected by FORTUNE as one of the “100 Best Companies to Work for” in the United States.

With many established products and services helping patients in more than 80 countries, Genzyme is a leader in the effort to develop and apply the most advanced technologies in the life sciences. The company’s products and services are focused on rare inherited disorders, kidney disease, orthopaedics, cancer, transplant and immune diseases, and diagnostic testing. Genzyme’s commitment to innovation continues today with a substantial development program focused on these fields, as well as heart disease and other areas of unmet medical need.

This press release contains forward-looking statements, including without limitation statements about: the increased use of Thyrogen and the anticipated publication of an article relating to the Thyrogen label correction. 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 actual effect of the new Thyrogen label on Thyrogen use; the accuracy of Genzyme’s information regarding the prevalence of thyroid cancer; additional analysis of the SF-36 data; 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 “Factors Affecting Future Operating Results” 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 period ended September 30, 2005. Genzyme cautions investors not to place undue 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 these statements.

Genzyme® and Thyrogen® are registered trademarks of Genzyme Corporation. All rights reserved.

Contact Information

Maria Cantor

Media Contact

Genzyme Corp.

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