Herceptin: Monoclonal Antibody for Breast Cancer Treatment

Herceptin (trastuzumab) was approved in 1998 for treating breast cancer patients who did not respond to chemotherapy. Herceptin was also approved as a first-line treatment for metastatic breast cancer when used in conjunction with Taxol.

The Mechanism of Action

Herceptin is a monoclonal antibody that specifically binds to HER2, a protein which is found on the surface of some normal cells and involved in regulating cell growth. Herceptin is able to slow the most aggressive form of metastatic breast cancer and yet without the severe side effects of traditional chemotherapy owing to its specific antigen antibody reaction. Herceptin is derived from part of a mouse antibody bioengineered to closely resemble a human antibody. In metastatic breast cancer, approximately 30% of tumors produce excess amounts of HER2, in which case, the cancer tends to be more aggressive. Herceptin specifically targets cancer cells which over express HER2, but is of no much benefit for those which do not.

Herceptin is the second monoclonal antibody approved to treat cancer. The first one is Rituxan, which was approved in 1997 for treating patients with one type of non-Hodgkin's lymphoma.

Clinical Applications

More than 1.6 million women have been diagnosed with breast cancer in the United States, and there are about 180,000 new cases diagnosed each year, according to the American Cancer Society. In a randomized controlled clinical trial, the breast cancer patients who received chemotherapy plus Herceptin had less rapid tumor growth with higher one-year survival rates. In another clinical trial, Herceptin was found effective when used alone for a group of breast cancer patients who had relapsed following previous chemotherapy for metastatic disease. In both clinical trials, the patients associated with highest levels of HER2 protein responded best to Herceptin.

To identify patients who may benefit from Herceptin requires a test of HER2 protein on the cancer tissue. Patient selection is needed as the use of Herceptin either alone or in combination with chemotherapy can result in a weakening of the heart muscle and possibly lead to congestive heart failure. This potentially life-threatening side-effect is most common in patients who receive Herceptin in combination with chemotherapy consisting of anthracyclines and cyclophosphamide (AC). For this reason, Herceptin is not approved to be used with AC. All patients treated with Herceptin should have their heart function assessed before starting treatment and be closely monitored during treatment. Physicians must exercise great caution for patients with heart problems.

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