Hormone Therapy for Breast Cancer
About two-thirds of women with breast cancer have tumors that contain hormone receptors. This means a tumor has receptors for the hormone estrogen (called ER-positive) or the hormone progesterone (PR-positive) or both. Hormone therapy is given to block these hormones and fight the cancer's growth. Women who are ER-positive are more likely to respond to hormone treatment than women who are ER-negative.
Tamoxifen for Breast Cancer
Tamoxifen (Soltamox, Nolvadex) is a pill taken daily and has been used consistently for decades to treat breast cancer. Tamoxifen can be used in women of any age, regardless of whether they've gone through menopause. Taking tamoxifen for 5 years has been found to reduce the chance of breast cancer recurrence and new breast cancers in women with ER-positive or ER-unknown breast tumors.
Doctors also use tamoxifen to treat breast cancer that has spread to other parts of the body. It's also given to prevent breast cancer in healthy women with a high risk of developing the disease.
Women taking tamoxifen are more likely to develop cancer of the uterus (endometrial cancer) than other women. They should have regular pelvic exams and tell their doctor about any abnormal uterine bleeding. Other risks from tamoxifen include deep vein thrombosis, blood clots in the lungs, stroke, and cataracts. Minor side effects include hot flashes and mood swings.
Tamoxifen also helps prevent osteoporosis, or weak bones.
Aromatase Inhibitors and Breast Cancer
Aromatase inhibitors are medications that treat breast cancer in both early stages and advanced ones. Aromatase inhibitors prevent estrogen from being made. They are effective only in women who are past menopause.
Anastrozole (Arimidex), exemestane (Aromasin), and letrozole (Femara) are aromatase inhibitors. They are used to treat ER-positive breast cancer, either following tamoxifen treatment or by themselves.
Another drug, palbociclib (Ibrance), works by blocking a protein that controls cell division. Therefore, it keeps cancer cells from dividing and growing. It is taken with letrozole.
There are other hormone therapy drugs used to treat breast cancer, too. Most, such as fulvestrant (Faslodex) and toremifene (Fareston), are used to treat metastatic breast cancer. Toremifene, like tamoxifen, blocks certain effects of estrogen and is used as a treatment for advanced breast cancer in postmenopausal women. Fulvestrant blocks estrogen receptors temporarily.