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Hormone Therapy for Breast Cancer

Hormone therapy works by blocking the estrogen that causes cell division. It is used for adjuvant therapy and for advanced cancers in patients with hormone receptor positive tumors. Over the past few years, many new anti-estrogen agents have become available. They generally act in one or more of the following ways:

• Blocking the hormone receptor itself
• Suppressing estrogen production
• Destroying the ovaries (which produce estrogen)

Types of Hormone Therapy

• Selective Estrogen Receptor Modulators (SERMs) - SERMs resemble estrogen in their chemical appearance and trick the breast cancer cells into accepting it in place of estrogen. Unlike estrogen, however, they do not stimulate breast cancer cell growth. Tamoxifen (Nolvadex) has been the standard hormonal agent used for breast cancer. Other SERMs being studied for breast cancer include toremifene, idoxifene, and droloxifene.

  • Tamoxifen may be used for any cancer stage in women of all ages who have hormone receptor-positive cancers. In addition, it is being used protect against cancer in high-risk women. When used as adjuvant therapy for early stage hormone receptor positive breast cancer, tamoxifen is for a total of five years as tolerated. Taking it longer appears to provide no additional advantages. Patients whose tumors are hormone receptor-negative do not benefit from tamoxifen.

  • The most concerning side effect is an increased risk for blood clots, which can, in rare cases, be life-threatening. There also appears to be an increased risk for uterine cancer. Other side effects include hot flashes, vaginal bleeding and discharge, and visual disturbances.

• Aromatase Inhibitors - These agents block aromatase, an enzyme that is a major source of estrogen in many major body tissues, including the breast, muscle, liver, and fat. These agents are showing great promise for breast cancer and do not have the same risks as tamoxifen (blood clots and uterine cancer). Aromatase inhibitors are classified as either _ nonsteroidal_ or steroidal agents.

  • Nonsteroidal Aromatase Inhibitors - The nonsteroidal aromatase inhibitors include anastrozole (Arimidex) and letrozole (Femara) which are used for patients with advanced breast cancer with hormone-receptor positive tumors. Anastrozole may be used for early breast cancer treatment in postmenopausal women. These agents have fewer side effects, but seem to be as effective as tamoxifen. Another newer nonsteroidal agent, vorozole (Rivisor) is currently being investigated.

  • Steroidal Aromatase Inhibitors - The steroidal aromatase inhibitors include exemestane (Aromasin - given orally) and formestane (Lentaron - given by injection). Exemestane is used in metastatic breast cancer for postmenopausal women who do not respond to tamoxifen.

• Selective Estrogen Receptor Downregulators (SERDs) - Selective estrogen receptor downregulators (SERDs) block estrogen in all tissues in the body. This class of medications includes fulvestrant (Faslodex) which has showen to be as effective as anastrozole in delaying time to disease progression in women with advanced breast cancer. Side effects are generally gastrointestinal problems and hot flashes.

• Progestins - Progestins, particularly megestrol (Megace), have been used in the treatment of advanced breast cancer when tamoxifen fails. Side effects include weight gain.

• Ovarian Ablation - This is the process of shutting down estrogen production by the ovaries. This can be accomplished chemically with medications or it can be done by removing the ovaries surgically or by destroying them with radiation. Risks include the development of osteoporosis, but a number of therapies are available that can help prevent bone loss.