The Women's Health Resource. On the web since 1997.

Classes of Breast Cancer Drugs

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)
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:

  • Aromasin (generic name, exemestane)
  • Femara (generic name, letrozole)
  • Arimidex (generic name, anastrozole) 
  • Megace (generic name, megestrol)

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.