December 1998 -- Herceptin (trastuzumab) is the newest drug for the management of metastatic breast cancer (breast cancer that has spread beyond the breast). It is a new type of drug and has a different mechanism of action than any other drug used to treat breast cancer.
Most cells in the body, including breast cancer cells, are dependent for their growth on growth factors, proteins that are made by cells in the body and then circulate in the blood. The circulating growth factors bind to protein receptors on cells and stimulate them to grow. Approximately 25-30% of breast cancers overexpress (have higher than normal amounts of) a receptor for an important growth factor called HER2 protein. Herceptin is a synthetic (man-made) antibody which binds and blocks the HER2 protein on breast cancer cells so that circulating growth factor cannot bind and stimulate the breast cancer cells to grow. Herceptin is given as an intravenous injection.
Herceptin is approved by the Food and Drug Administration (FDA) for use alone or in combination with another drug, paclitaxel, in the treatment of metastatic (disseminated) breast cancers that overexpress HER2. Therapy with Herceptin alone is reserved for patients who have received other chemotherapy regimens, and combination therapy is used in patients who have not previously received chemotherapy. Herceptin is effective only in the treatment of tumors that overexpress HER2.
In clinical trials, patients who received Herceptin in combination with other chemotherapy had slower growth of their breast cancers and better survival after one-year of therapy as compared to patients who received only chemotherapy. The one year survival is 79% when Herceptin is used in combination with other chemotherapy and 61-73% when Herceptin is not included in the chemotherapy regimen. Herceptin, however, did not cure breast cancer. Patients with greater overexpression of HER2 have a better response to Herceptin than patients with lesser overexpression. Herceptin also seems to be more effective when it is used in combination with other chemotherapy.
The most serious adverse effect of Herceptin is congestive heart failure. In premarketing studies, heart failure occurred in 7% of patients in whom Herceptin was used alone and 28% in patients in whom it was combined with other chemotherapy (cyclophosphamide and the anthracyclines, doxorubicin or epirubicin). The most common adverse effects have been pain, nausea, diarrhea, fever, chills, headache, insomnia, rash, cough, dyspnea (difficulty breathing) and dizziness.
Studies have not been performed to determine if Herceptin interacts with other drugs. As with all new drugs, more information will be obtained during postmarketing studies.
For more up-to-date information on breast cancer, and current treatments, please visit the MedicinNet.com Breast Cancer Center.