Systemic Therapies for Breast Cancer
Nearly 50 years ago, clinical scientists wondered whether it might be more effective to treat all patients with systemic therapies before their cancer grew into detectable metastases, rather than waiting for these to occur. Such a strategy is called "adjuvant" systemic therapy. Many prospective randomized clinical trials have consistently shown that adjuvant therapy is much more effective in improving survival than delaying therapy until, or if, a patient develops metastases.
Anti-Estrogen TherapiesEstrogen can promote the development of some cancers in the breast. The most widely used anti-estrogen therapy is tamoxifen, a drug that blocks the effects of the hormone estrogen in the breast. As adjuvant therapy, tamoxifen helps prevent the original breast cancer from returning. It also helps prevent the development of new cancers in the other breast. As treatment for metastatic breast cancer, the drug slows or stops the growth of cancer cells that are present in the body.
Other anti-estrogen therapies include removing ovaries, or stopping their function by medical treatment, in women who are still menstruating. These treatments are called ovarian ablation. Ongoing studies are addressing whether premenopausal women should only receive tamoxifen, or if they should have ovarian ablation and then receive tamoxifen or an aromatase inhibitor (AI).
An aromatase inhibitor is a drug that prevents the formation of estradiol, a female hormone, by interfering with an enzyme. Aromatase inhibitors are used as a type of hormone therapy for postmenopausal women who have hormone-dependent breast cancer.
There are three aromatase inhibitors on the market: anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). Currently, none of these appears to be superior to the others with respect to activity or side effects, so a patient might receive any one of the three.
Anti-HER2 TherapiesHER2 is a protein that sits on the surface of a cancer cell and helps control the signals from outside the cell to the nucleus. An anti-HER2 therapy helps to keep the protein from working.
The most important anti-HER2 therapy to date is called trastuzumab (Herceptin). Trastuzumab binds to HER2 and keeps it from working within the cell. Trastuzumab does not seem to work in cells that do not make HER2.
Another anti-HER2 drug is lapatinib (Tykerb). It acts by entering a cancer cell and binding to the part of the HER2 protein that lies beneath the surface of the cell.
ChemotherapyChemotherapy is treatment with drugs. Chemotherapy works in many ways, but basically it targets cells that are dividing rapidly. Therefore it is not as specific as anti-estrogen or anti-HER2 therapy and has more side effects. Large randomized trials have demonstrated that overall chemotherapy reduces the chances of distant metastases by approximately 30%.
The decision to use chemotherapy or not is based on the risk of distant metastases, and is not in any way reduced if a patient elects to have a mastectomy. Thus, the surgical therapy decision should not be made in hopes of avoiding chemotherapy.
There are many drugs that are effective against breast cancer cells. These drugs are frequently combined into regimens. Treatments may be given every day, every week or every month. The treatment period is followed by a period of rest, with no chemotherapy, to give your body a chance to build healthy new cells.
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