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Classes of Drugs Used to Treat Breast Cancer
| Class |
Action |
Examples* |
| SERMs (Selective Estrogen-Receptor Modulators) |
Bind to estrogen
receptors in breast cancer cells, starving cancer cells |
Tamoxifen
Evista (raloxifene)
Fareston (toremifene) |
Aromatase
Inhibitors |
Prevent production of
estrogen in adrenal glands |
Aromasin (exemestane)
Femara (letrozole)
Arimidex (anastrozole)
Megace (megestrol) |
| Biologic Response Modifiers |
Bind with certain
proteins on breast cancer cells, preventing their growth |
Herceptin
(trastuzumab) |
| Other Hormonal Therapies |
Treat breast cancers
that are dependent on estrogen for survival |
Zoladex (goserelin
acetate)
Faslodex (fulvestrant) |
*Generic names of drugs are shown in
parentheses.
SERMs (selective estrogen-receptor modulators): These drugs
bare a chemical resemblance to the hormone estrogen. Many breast cancers are
"estrogen-dependent," meaning that they depend on estrogen in order to survive
and reproduce. Because SERMs mimic estrogen, they are able to bind to estrogen receptors
in breast cancer cells. By binding to these receptors, they block estrogen from breast
cancer cells, thereby starving the cancer cells.
Tamoxifen is currently the
most commonly prescribed SERM. Tamoxifen is approved by the U.S. Food and Drug
Administration (FDA) to help treat both early and advanced stages
of breast cancer. Recently, tamoxifen also received FDA approval for use in
post-menopausal women at high risk of breast cancer after a large clinical trial showed that tamoxifen could reduce the risk
of breast cancer by 49%. The drug Fareston (generic
name, toremifene) is another SERM used to treat advanced breast
cancer.
Another SERM, Evista (generic name, raloxifene) is
used to treat osteoporosis, a degenerative bone disease. In clinical trials, raloxifene was
shown to reduce the risk of breast cancer in high-risk post-menopausal women by 44 to 71 percent.
Researchers are also investigating another SERM called arzoxifene for the treatment of breast cancer. Arzoxifene
is made by the same company as raloxifene (Eli Lilly and Company) and is described to be a next-generation
SERM. The drug is currently in Phase III clinical trials.
Aromatase inhibitors: These drugs work by binding to the
body’s aromastase enzyme, an enzyme responsible for producing estrogen. Many breast
cancer cells depend on estrogen to grow and multiply quickly. Once the aromatase inhibitor
has binded to the aromastase enzyme, estrogen cannot be produced by the enzyme. This lack
of estrogen starves cancer cells, preventing them from growing and dividing.
There are several aromatase inhibitors that are used to help treat advanced breast
cancer including:
Recent studies suggest that some aromatase inhibitors may be more effective than
tamoxifen in treating advanced breast cancer or may be useful
after patients become resistant to tamoxifen. For example, Femara was recently FDA
approved as an initial treatment option in advanced breast cancer patients after data
showed that Femara may work better than tamoxifen in some patients (i.e., slows the
growth of cancer and improves survival time). Recent studies also show that both Arimidex
and Femara many be more effective than Megace for treating breast cancer.
Biologic response modifiers: These drugs bind with
certain proteins on breast cancer cells, preventing their growth. The drug Herceptin (generic name, trastuzumab) is a monoclonal antibody
that attaches itself to HER2 (also written HER2/neu), a
protein found on breast cancer cells. Approximately 30% of breast cancer patients have
extra copies of the HER2 protein, which can signal more aggressive cancers. Herceptin
binds to HER2 receptors on breast cancer cells, preventing them from growing and dividing.
Herceptin is only indicated for breast cancer patients who overexpress the HER2 protein.
Patients should be tested for HER2 expression to determine whether Herceptin is a viable
treatment option.
Other hormonal therapies: Hormone therapies are used to
treat breast cancers that are dependent on estrogen for survival. In addition to SERMs and
aromatase inhibitors, there are several other hormonal therapies used to treat breast
cancer. For example, the drug Zoladex (generic name,
goserelin acetate) is a synthetic form of the body’s lutenizing hormone-releasing
hormone (LHRH). Zoladex blocks the release of estrogen in breast cancer patients (and
testosterone in prostate cancer patients), preventing breast and prostate cancer cells
from growing.
Another hormone therapy, Faslodex (generic name,
fulvestrant), appears to be effective for women who have become resistant to tamoxifen,
according to recent studies. Instead of binding to estrogen receptors in breast cancer
cells like tamoxifen, Faslodex destroys estrogen receptors in cancer cells.
CONTINUED
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