Women who are high risk for developing breast cancer may want to consider chemoprevention: taking a hormone therapy that reduces estrogen in the breast. Available drugs include tamoxifen, raloxifene (Evista), or the aromatase inhibitor exemestane (Aromasin).
Tamoxifen and raloxifene are selective estrogen receptor modulators (SERMs). Tamoxifen is used to treat breast cancer. Raloxifene is an osteoporosis drug that was later found to reduce breast cancer. However, raloxifene is only used for risk reduction, not treatment. Both drugs are associated with an increased risk for blood clots, hot flashes, and vaginal bleeding. Exemestane is used to treat breast cancer in postmenopausal women. Its side effects include arthritis and hot flashes; it does not increase risk for osteoporosis or blood clots.
The National Cancer Institute’s Breast Cancer Risk Assessment Tool is used to assess breast cancer risk. It is a questionnaire you can complete online that assess risk based on a woman’s age, race, and medical and reproductive history. You are considered high risk if your risk of developing breast cancer in the next five years is greater than 1.66%.
Chemoprevention drugs, which are taken for five years, have been shown to cut breast cancer risk in half. What does that mean? In the randomized trials that looked at breast cancer risk in high-risk women, about four percent of the women who did not take chemoprevention developed breast cancer compared with two percent of the women who did take a chemopreventive drug for five years.
Chemoprevention should not be used in women with a prior history of deep vein thrombosis, pulmonary embolus, stroke, or transient ischemic attack (TIA), or in combination with menopausal hormones. For women taking tamoxifen or raloxifene, gynecological exams should be done before starting treatment and yearly thereafter to monitor for uterine cancer. Raloxifene and exemestane are recommended only for postmenopausal women. Tamoxifen can be used by pre- and postmenopausal women. Premenopausal women cannot become pregnant while taking tamoxifen, as it may increase the risk for certain birth defects.