Estrogen, the main female sex hormone, is produced mostly by the ovaries. It triggers a woman’s sexual development, including the growth of breasts and regulation of her menstrual cycle. At menopause, usually around age 51, the ovaries stop producing estrogen, but small amounts are still made from pre-hormones (substances that are converted to hormones) produced by the adrenal glands (small glands on top of your kidneys). These pre-hormones are then changed into estrogen by fat tissue.
Estrogen travels through the bloodstream and attaches to certain cells in your body. Breast tissue has these types of cells and is one of the main targets for estrogen. Estrogen stimulates the growth of breast cells. For this reason, if a woman develops cancer cells in her breast, estrogen can promote the growth of that cancer.
Breast cancer is one of the most common cancers in women. Women are at increased risk if they are older or overweight, and if they are:
You can lower your risk of breast cancer by following a healthy lifestyle that includes a well-balanced diet, regular exercise, and limiting alcohol to no more than one drink a day. You can also limit your exposure to estrogen by losing weight if overweight, and by avoiding sources of combination hormone replacement therapy after menopause. The use of estrogen-only hormone therapy for less than five years does not appear to increase the risk of breast cancer, but more information is needed about the safety of estrogen therapy used for longer than five years.
If you are at high risk of developing breast cancer, your doctor may recommend a class of drugs called selective estrogen receptor modulators (SERMs). The U.S. Food and Drug Administration (FDA) has approved two SERMs to prevent breast cancer:
Tamoxifen and raloxifene only reduce the risk of breast cancer by 50%. The decision to take these medications always depends on the balance between the benefits and risks. Side effects can include uterine cancer (with tamoxifen only), stroke, and blood clots in the veins and lungs. Your doctor will work with you to find the best option for you.