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Cancers that have hormone receptors in the cells (are ER-positive or PR-positive) are called hormone receptor-positive. In those cancers, the female hormone estrogen promotes the growth of the cancer. Hormone therapy for breast cancer works by blocking the effects of estrogen or lowering estrogen levels.

Hormone therapy can be used to help reduce the risk of the cancer coming back after surgery. It is also helpful in treating advanced breast cancer.

Tamoxifen, toremifene, and fulvestrant (Faslodex®) are drugs that block the effect of estrogen in breast cells.

Anastrozole (Arimidex), exemestane (Aromasin), and letrozole (Femara) are aromatase inhibitors (AIs). These drugs stop fat tissue from making estrogen. They only lower estrogen levels if the ovaries aren’t working (like after menopause).

Luteinizing hormone-releasing hormone (LHRH) analogs are drugs that lower estrogen levels in women who haven’t gone through menopause by shutting down the ovaries.

Surgery to remove the ovaries can be used instead of LHRH analogs to lower estrogen levels in women who have not gone through menopause.

Common side effects of these drugs include symptoms of menopause, such as hot flashes, night sweats, and vaginal dryness. The aromatase inhibitors also can cause bone and muscle pain. Tamoxifen and toremifene are also rarely linked to serious blood clots and cancer of the uterus.

More information about hormone therapy for breast cancer can be found in the Breast Cancer detailed guide.

Last Medical Review: 09/09/2014
Last Revised: 01/14/2016