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Systemic treatments have improved immensely over the last two decades. Treatment options for patients who have developed metastatic breast
cancer have more than doubled since 1980, and the lives of most patients with metastatic disease are improved greatly. However, patients
with metastatic breast cancer are rarely, if ever, cured; currently available therapies can prolong life but almost never make the cancer
go away completely.
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 Therapies
Estrogen 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 Therapies
HER2 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.
Chemotherapy
Chemotherapy 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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