JOYCE O'SHAUGHNESSY, MD: You know we used to think we had just one kind of breast cancer to treat. But now it's clear that we have at least four different kinds.
ERIC WINER, MD: We're learning more and more that different types of breast cancer should be treated quite differently.
ANNOUNCER: The differences stem from variations in markers on the surface of the cancer cells and genes with the cells.
GABRIEL HORTOBAGYI, MD: More than 90 percent are the result of genetic changes acquired during life. And these changes not only determine the development of breast cancer, so the change from normal breast tissue to malignant breast tissue, but also give special behavioral characteristics to the tumor.
ANNOUNCER: Lab tests done on breast cancers can distinguish between these different sub-groups of breast cancer.
JOYCE O'SHAUGHNESSY, MD: It's critically important that a few specific tests be done on all women's breast cancers who are newly diagnosed with breast cancer to find out what kind they have.
ERIC WINER, MD: The tests we use to define this in the clinic are essentially pretty simple tests that measure estrogen receptor, progesterone receptor and HER2.
ANNOUNCER: Treatment decisions are based on the results of these tests. More than three-quarters of breast cancers are sensitive to the hormones estrogen or progesterone.
ERIC WINER, MD: The importance of estrogen receptors and progesterone receptors is that these define a group of tumors where we can use hormonal therapy.
ANNOUNCER: Additionally, about 20 percent of breast cancers have an increased number of a receptor known as HER2, a protein involved in the regulation of cell growth.
JOYCE O'SHAUGHNESSY, MD: Herceptin is the standard of care with chemotherapy for women whose breast cancers are HER2-positive.
ANNOUNCER: Herceptin or trastuzumab is an antibody therapy that targets the HER2 receptor.
ERIC WINER, MD: It is thought that trastuzumab hooks onto the outside of the cancer cell, to that protein that's sitting on the surface of the cancer cell the HER2 protein. And that as a result of binding to that HER2 protein, it essentially turns off some activity that had been going on in the cancer cell, activity that led the cancer cell to divide more rapidly.
JOYCE O'SHAUGHNESSY, MD: If you take out that survival signal with the Herceptin, which is that specific treatment that binds to the HER2, then the cells die a whole lot better with the chemotherapy.
ANNOUNCER: Trastuzumab plus chemotherapy is given as adjuvant therapy to patients whose cancers are HER2-positive following lumpectomy or mastectomy.
JOYCE O'SHAUGHNESSY, MD: The purpose of it is in case there are cells that broke off from that original breast cancer and traveled through the blood stream or through the lymphatics to parts of the body. We have to give the chemotherapy and the Herceptin as an adjuvant, additional therapy to kill off those cancer cells that may have traveled some place in the body.
ANNOUNCER: Patients with metastatic HER2-positive breast cancer are treated with trastuzumab alone or in combination with chemotherapy.
JOYCE O'SHAUGHNESSY, MD: We don't have a cure. We can control their disease with the Herceptin and the chemotherapy, sometimes for long periods of time. Some women, unfortunately, will have the cancer still come back
ANNOUNCER: The FDA recently approved Tykerb, also known as lapatinib, for some of these patients.
ERIC WINER, MD: There are studies going on looking at the combination of trastuzumab and lapatinib. And there are combinations with both of these drugs or each of these drugs and many, many other biologic approaches, either with or without chemotherapy. I do think that it may well be the case that combinations of these drugs will work better than the drugs being given by themselves.
ANNOUNCER: Whether for advanced disease or for breast cancer that has not spread, doctors say good treatment increasingly depends on careful differentiation between subtypes of disease.