Some types of breast cancers are affected by hormones in the blood. Hormone therapy for breast cancer is a treatment for breast cancers that are sensitive to these hormones.

Why Hormone Therapy is Used in Breast Cancer Treatment

The female hormones estrogen and progesterone stimulate certain breast cancers. Doctors refer to these cancers as Estrogen receptor positive (ER-positive) or Progesterone receptor positive (PR-positive). The goal of hormone therapy is to slow or prevent cancer growth by blocking the body’s ability to produce hormones or by interfering with the effects of hormones on breast cancer cells.

Types of Hormone Therapy Used for Breast Cancer

Several strategies are used to treat hormone-sensitive breast cancer. These include selective estrogen receptor modulators, aromatase inhibitors, selective estrogen receptor downregulators, and ovarian suppression. These strategies are used in combination with other therapies like breast cancer surgery, chemotherapy and radiation therapy.

Selective estrogen receptor modulators

Selective estrogen receptor modulators (SERMs) are drugs that prevent breast cancer cells from binding to estrogen. They do this by sitting in the estrogen receptors in the breast tissue. When a SERM is in the estrogen receptor, there is no room for estrogen, therefore prohibiting it from attaching to the cell.

Tamoxifen (Nolvadex®) and Toremifene (Fareston®) are the most commonly used SERMs. Each of these drugs are taken orally, most often as a pill, and can be used to treat women both before and after menopause.

Aromatase Inhibitors

Drugs called aromatase inhibitors are used to block the activity of an enzyme called aromatase, which the body uses to make estrogen in the peripheral tissues. Typically, aromatase inhibitors are primarily used among postmenopausal women. This is because the ovaries in premenopausal women produce too much aromatase for the inhibitors to block effectively. Anastrozole (Arimidex®), letrozole (Femara®), and exemestane (Aromasin®) are the most common AIs used in hormone therapy.

Selective estrogen receptor downregulators

Selective estrogen receptor downregulators, or SERDs, block the effects of estrogen in breast tissue.  At this time, Fulvestrant (Faslodex®) is the only SERD available to treat hormone-receptor-positive breast cancer. Fulvestrant is similar to SERM drugs in that it sits in the estrogen receptors in breast cells. The difference, however, is that it is a pure antiestrogen. Furthermore, when Fulvestrant binds to the estrogen receptor, the receptor is targeted for destruction.

Ovarian Suppression

Since most of the estrogen in premenopausal women is made by the ovaries, suppressing or permanently removing them can be an effective treatment. This suppression of the ovaries, which allows the hormone therapies to work better, is called ablation. Ovarian ablation can be done surgically (oophorectomy) or medically (drugs).

Side Effects of Hormone Therapy

Side effects vary depending on the type of hormone therapy used. Common side effects may include:

• Hot flashes and night sweats
• Fatigue
• Loss of sex drive
• Mood swings
• Irregular periods or spotting
• Vaginal dryness or itching
• Joint and muscle pain
• Loss of bone density

Hormone therapy can also disrupt the menstrual cycle in premenopausal women.

Can Hormone Therapy be Used to Prevent Breast Cancer?

Yes. Most breast cancers are hormone-receptor positive, and clinical trials have tested whether hormone therapy can be used to prevent breast cancer in women who have a higher risk of developing the disease. Currently, the only two drugs approved by the FDA to prevent breast cancer are Tamoxifen® and Raloxifene®. However, studies have shown that Aromatase inhibitors are also useful in preventing breast cancer in postmenopausal women.