Breast Cancer: Endocrine or Hormone Therapy

Who should get endocrine therapy?


About two-thirds of breast cancer cells have receptors where hormones, such as estrogen and progesterone, can attach. These hormones help the cancer cells multiply quickly. This is known as hormone-receptor positive breast cancer.


Endocrine therapies block or decrease hormones to stop the growth of cancers that have hormone receptors. They also are called hormone therapies or anti-estrogen therapies. A patient whose breast cancer is hormone-receptor positive usually will be offered endocrine therapy.


Endocrine therapy fights cancer by reducing or blocking the production or effects of hormones. It may be given after surgery, chemotherapy and radiation. Endocrine therapy reduces the risk of breast cancer coming back and reduces the risk of a new breast cancer. Research shows that these drugs also help prevent breast cancer.


If you do not have hormone-receptor positive breast cancer, you will not benefit from endocrine therapy and it will not be offered.


Why do I need endocrine therapy?


Endocrine therapy is given to:

  • Prevent cancer from coming back (recurrence)
  • Slow the growth of cancer
  • Control symptoms caused by cancer

Your medical oncologist will plan your treatments based on the:

  • Type of cancer
  • Location of the cancer
  • Side effects that cancer or treatments could have on your body and health

How will I receive endocrine therapy?


The most common endocrine therapies involve:

  • Taking a pill by mouth (orally), either an estrogen-blocker or an aromatase-inhibitor
  • Receiving an injection (shot) under the skin or into a muscle
  • Having surgery to remove the ovaries

Drugs That Block Estrogen


Estrogen-blockers prevent estrogen from affecting the breast and other tissues. They are prescribed most often for premenopausal women and sometimes for postmenopausal women. Tamoxifen (Nolvadex) is a commonly prescribed estrogen-receptor blocker.


Drugs That Lower Estrogen


Aromatase inhibitors stop the production of estrogen in the body and lead to very low levels of estrogen. They are currently approved for use only in women who have gone through menopause (although in some clinical trials premenopausal women are being treated with aromatase inhibitors if their ovaries are suppressed or removed). Anastrazole (Arimidex), letrozole (Femara) and exemestane (Aromasin) are three commonly used aromatase inhibitors.


Frequently Asked Questions about Endocrine Therapy for breast cancer