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Breast Cancer: Comparing Hormone-Blocking Treatments

Topic Overview

When breast cancer is described as estrogen-receptor-positive (ER+), it means that estrogen helps these breast cancer cells grow. Hormone therapy is used in ER+ breast cancer to reduce the body's production of estrogen or to block its effects. This is done to stop the growth of cancer cells.

Hormone-blocking treatments, such as tamoxifen or an aromatase inhibitor, act on cells all over the body but generally cause fewer side effects than chemotherapy. If you are deciding what type of medicine to use, weigh the side effects and risks along with the benefits for your type of cancer.

Comparing hormone-blocking treatments

Drug names

tamoxifen (Nolvadex) anastrozole (Arimidex), exemestane (Aromasin), letrozole (Femara)

Class of drug

Selective estrogen receptive modulator (SERM)Aromatase inhibitor

What it does

Blocks harmful estrogen in the breastLimits how much estrogen the body makes

Treats breast cancer?

Yes, before and after menopauseYes, after menopause (instead of or after tamoxifen)

Side effects and risks

Side effects can include hot flashes and vaginal dryness.

Increased risks of:

Side effects can include hot flashes, vaginal dryness, muscle/body ache, mild nausea, diarrhea/constipation, weakness, and fatigue.

Increased risk of osteoporosis after 5 years of treatment for women who started out with weak bones (osteopenia)

When taking tamoxifen, you will need a pelvic exam every year. If you have any vaginal bleeding, other than normal menstrual bleeding, tell your doctor as soon as possible. This can be a sign of uterine precancer or cancer.

Neither chemotherapy nor hormone therapy is likely to cure breast cancer that has spread to another area of the body (metastasized). But each of these treatments can reduce symptoms and may prolong life.


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