Hormone Therapy for Breast Cancer
The hormones estrogen and progesterone, which help regulate body cycles like menstruation, can also cause breast cancer to grow. Hormone therapy is a treatment for breast cancers that are fueled by these hormones.
Why Hormone Therapy is Used in Breast Cancer Treatment
Certain breast cancers are stimulated by the female hormones estrogen or progesterone. Doctors refer to these cancers as estrogen receptor-positive (ER-positive) or progesterone receptor positive (PR-positive). Hormone therapy aims 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
There are several strategies used to treat hormone-sensitive breast cancer, including selective estrogen receptor modulators, aromatase inhibitors, estrogen receptor downregulators, and ovarian suppression. These are often used in combination with other therapies that are used to remove the cancerous cells, including breast cancer surgery, chemotherapy, and radiation therapy.
Selective estrogen receptor modulators
Also called SERMs, these drugs 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.
The most commonly used SERMs are Tamoxifen (Nolvadex®) and Toremifene (Fareston®). Both of these drugs are taken by mouth, most often as a pill, and can be used to treat women both before and after menopause.
Drugs called aromatase inhibitors are used to block the activity of an enzyme called aromatase, which the body uses to make estrogen in the ovaries and in other tissues. In most cases, 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. Common AIs include anastrozole (Arimidex®), letrozole (Femara®), and exemestane (Aromasin®).
Estrogen receptor downregulators
Estrogen receptor downregulators, or ERDs, block the effects of estrogen in breast tissue. Currently, fulvestrant (Faslodex®) is the only ERD available to treat hormone-receptor-positive breast cancer. Like the SERMS drugs, fulvestrant sits in the estrogen receptors in breast cells. The difference, however, is that it is a pure antiestrogen. Additionally, when fulvestrant binds to the estrogen receptor, the receptor is targeted for destruction.
Because most of the estrogen in premenopausal women is made by the ovaries, permanently removing or suppressing them can be an effective treatment. Suppressing ovarian function is called ovarian ablation, and this will allow the hormone therapies to work better. Ovarian ablation can be done surgically (oophorectomy) or medically (drugs).
Side Effects of Breast Cancer Hormone Therapy
Different hormone therapies have different side effects. Common side effects may include:
- Hot flashes and night sweats
- Loss of sex drive
- Irregular periods or spotting
- Vaginal dryness or itching
- Mood swings
- Loss of bone density
- Joint and muscle pain
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. At this time, Tamoxifen® and Raloxifene® are the only two drugs approved by the FDA to prevent breast cancer, however, other studies are underway.