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May 3, 2000

Dear Healthcare Provider:

Genentech®,Inc. wants to alert you to 62 postmarketing reports of serious adverse events related to the use of HERCEPTIN® (Trastuzumab); some of these events resulted in a fatal outcome. These serious adverse events are characterized by one or more of the following categories: hypersensitivity, infusion, and pulmonary reactions. Fifteen patients experienced pulmonary and other adverse events following HERCEPTIN use, which culminated in a fatal outcome. Nine of these patients had onset of symptoms within 24 hours of infusion and subsequently died. It is estimated that 25,000 patients have been treated with HERCEPTIN worldwide since marketing approval.

Based on this new information, HERCEPTIN product labeling will be modified with additions to the BOXED WARNING, WARNINGS, and ADVERSE REACTIONS sections to include:

Hypersensitivity reactions, including fatal anaphylaxis

Infusion reactions, including some with a fatal outcome

Pulmonary events, including adult respiratory distress syndrome and death

While some of the serious adverse events mentioned above were observed in clinical trials, some of the events reported in the postmarketing setting were more severe. Additionally, the following observations have not been previously reported: adult respiratory distress syndrome, anaphylaxis, and death within 24 hours of a HERCEPTIN infusion.

Serious adverse events of greater severity than previously reported include: urticaria, bronchospasm, angioedema, hypotension, dyspnea, wheezing, pleural effusions, pulmonary infiltrates, noncardiogenic pulmonary edema, and pulmonary insufficiency and hypoxia requiring supplemental oxygen or ventilatory support.

In the majority of patients the symptoms occurred with the first dose of HERCEPTIN. While the time of onset of symptoms most often occurred during the infusion or within the first 12 hours following the infusion, events were also reported to have occurred 24 hours or more after the infusion. In some cases, patients improved after the initial reaction, but experienced marked clinical deterioration at a later time point. In a small number of cases the patients died at home.

Most patients with fatal events had significant pre-existing pulmonary compromise secondary to intrinsic lung disease and/or malignant pulmonary involvement. Because it appears that patients with significant pre-existing pulmonary compromise may be at greater risk, these patients should be treated with extreme caution. Patients experiencing any of the severe infusion-associated symptoms mentioned above, or in the prescribing information, should have the HERCEPTIN infusion discontinued and appropriate medical therapy administered. Patients should be closely monitored until complete resolution of their symptoms. In addition, patients should be informed of the possibility of delayed severe reactions.

Updated labeling containing more detailed information in the BOXED WARNING and WARNINGS sections of the HERCEPTIN package insert will be available shortly. Should you have any questions regarding the use of HERCEPTIN, please call our Medical Information Department at 1-800-821-8590.

Healthcare professionals should report any serious adverse events suspected to be associated with the use of HERCEPTIN to Genentech at 1-800-626-3553, extension 57541. Alternatively, this information may also be reported to the FDA's MedWatch reporting system by phone (1-800-FDA-1088), by facsimile (1-800-FDA-0178), or on-line (https://www.accessdata.fda.gov/scripts/medwatch) or mailed, using the MedWatch form FDA 3500, to the FDA Medical Products Reporting Program, 5600 Fishers Lane, Rockville, MD 20852-9787.

Sincerely,

Executive Vice President
Chief Medical Officer
Genentech, Inc.