Hormone therapy uses drugs to inhibit the activity of hormones such as estrogen and progesterone, that support the growth and spread of cancer cells. Hormonal systemic treatment of breast cancer involves taking a pill by mouth, usually twice a day. For estrogen-receptor negative tumors, or tumors not fed by estrogen, one would not consider hormone therapy. Tamoxifen is the most common hormone treatment used and has been available for use the longest. It is a selective estrogen receptor modulator, which means it has anti-estrogen effects on hormone-receptor positive breast cancer and estrogenic effects on some other tissues, such as bones and the uterus.

Another class of hormonal agents, aromatase inhibitors, includes anastrozole (Arimidex), letrozole (Femara) and exemestane (Aromasin). In post-menopausal women, fatty tissue can be converted into estrogen by the using an enzyme called aromatase, and aromatase inhibitors block this process. In addition to aromatase inhibitors, there is an approach to destroying estrogen receptors called fulvestrant (Faslodex), which is given by monthly injections.

Side Effects

Serious side effects of various hormone therapies include increased risks for other cancers, bone thinning and osteoporosis, and abnormal clotting of the blood. Side effects with hormone therapy can include weight gain, hot flashes, vaginal dryness, and nausea.