Estrogen Receptor-Positive Tumors

Some breast cancers are sensitive to the female hormone, estrogen, and are called "estrogen receptor-positive." The drug tamoxifen interferes with estrogen and when breast cancer cells are sensitive to estrogen, tamoxifen can inhibit their growth.

Studies have shown that tamoxifen improves the chances of survival and helps prevent recurrence of breast cancer, if the cancer cells are estrogen receptor-positive. Tamoxifen is not an effective treatment for breast cancer that is estrogen receptor-negative, and therefore should not be taken for those cancers. Tamoxifen may have unpleasant side effects that are similar to menopause, such as hot flashes, vaginal dryness, irregular periods, and weight gain. Tamoxifen also slightly increases the risk of uterine cancer and blood clots. Studies suggest that Tamoxifen should not be taken for more than five years