What Is Herceptin and What Are Its Side Effects?

— -- Question: What is Herceptin and what are its side effects? What are its potential side effects versus benefits?

Answer: Herceptin is a drug, an agent whose chemical name is 'trastuzumab.' It's a monoclonal antibody that interferes with the function of an important protein in some breast cancers: the HER2 protein. About 20 or 25 percent of breast cancers over-express the HER2 protein. Those breast cancers seem to be those whose growth is sometimes stimulated by this particular pathway, and Herceptin can interfere with this growth pathway.

We know from studies that have been done that Herceptin, when used by itself for women whose breast cancers over-express the HER2 protein in advanced breast cancer, can help to slow the growth of the breast cancer or even reduce its size. Because of that, we have done studies that suggested that Herceptin added to chemotherapy in the setting of metastatic breast cancer can also lead to an improvement in breast cancer.

Because of those positive results, and because the side effect profile is pretty low, we have now conducted studies of the use of Herceptin for a specific period of time in women who have earlier stages of breast cancer -- particularly those who have lymph node-positive breast cancer that over-expresses the HER2 protein. From many clinical trials done around the world in the last several years, we know that the use of Herceptin will decrease the chances of breast cancer recurrence by about one-half in those women who received Herceptin in addition to their prescribed chemotherapy and hormone therapy.

And as a consequence, most oncologists and patients will think about the role of Herceptin in the setting of early breast cancer, especially lymph node-positive breast cancer, where the HER2 protein is over-expressed.

Herceptin has relatively few side effects, but certainly the one that has troubled us the most is that there is a small, but real, chance of developing heart damage as a consequence of Herceptin, particularly if it's used in close proximity to certain of the chemotherapy drugs --