Hormone Therapy for Breast Cancer

Many types of breast cancer are hormone-responsive, meaning they depend on the reproductive hormones that the body naturally produces, such as estrogen and progesterone, to fuel their growth. If diagnostic testing suggests that your tumor is hormone-responsive, as is the case in an estimated 75% of breast cancers, your doctors may recommend hormone therapy as part of your treatment plan.

Estrogen and Breast Cancer

Learn more about the estrogen-breast cancer connection and hormone-receptor testing for breast cancer.

The goal of hormone therapy is to prevent estrogen and progesterone from stimulating the growth of any cancer cells at the tumor site itself or that may have traveled through the lymph system to other parts of the body.

Hormone therapies primarily target the hormone estrogen, since it is most closely associated with breast cancer growth. Like chemotherapy, hormonal therapy can affect cells throughout the body, so it’s considered a systemic treatment. There are two main approaches oncologists use to block the effect of estrogen on cancer cells:

Ovariectomy, or surgical removal of the ovaries, is not performed as hormone therapy in post-menopausal women. That’s because the ovaries stop producing estrogen after menopause, so removing them would have no benefit.

See a medical animation about the uses of ovariectomy, or oophorectomy.

  • Medical hormone therapy. Some drugs prevent estrogen from binding to cancer cells. Others prevent the body from making the estrogen that causes breast cancer to grow.
  • Surgical hormone therapy. If you have not yet gone through menopause, your doctor may recommend surgery to remove your ovaries, which is where most of the body’s estrogen is created. This procedure is called an ovariectomy or an oophorectomy.

There are several classes of medical hormonal therapy. Each works in a different way. Learn about:

Selective estrogen receptor modulators, or SERMs

Stopping Hormone-Responsive Tumors

Learn more about hormone therapy in Your Guide to Cancer Care.

Because estrogen must bind to the estrogen receptors in breast cancer cells to stimulate growth, medicines that prevent estrogen from attaching to cancer cells may be able to block that growth. SERMs work by binding to estrogen receptors — essentially occupying the estrogen’s “parking spot” on the cancer cells. This blocks the body’s estrogen from reaching the cancer cells, preventing the hormone from fueling their growth.

Currently, tamoxifen is the most well-known and widely used SERM. Oncologists use tamoxifen to treat people with hormone-responsive cancers of all stages, both early and more advanced. It’s also used preventively, with both people who are at high risk of developing breast cancer, and those who have been previously treated and are at risk of having a recurrence.

Tamoxifen has the added advantages of keeping bones strong and cholesterol low throughout the course of breast cancer treatment.

Aromatase inhibitors

This class of hormone therapy drugs is designed to block estrogen production by binding to the enzyme responsible for producing the hormone, the aromatase enzyme. Once production is stopped, the cancer cells starve from lack of estrogen, which prevents them from growing and dividing.

Some well-known aromatase inhibitors are:

  • Femara, known generically as letrozole, is used to treat people with advanced breast cancer. It may also offer an alternative treatment for people who are resistant to tamoxifen.
  • Arimidex, known generically as anastrozole, is used to treat advanced breast cancer.
  • Aromasin

Other medical hormone therapies

Besides SERMs and aromatase inhibitors, other types of hormone therapies used in breast cancer treatment include:

  • Zoladex, known generically as goserelin acetate, blocks the release of estrogen by mimicking the body’s luteinizing hormone-releasing hormone (LHRH).
  • Faslodex, or fulvestrant, destroys estrogen receptors in breast cancer cells instead of binding to the receptors. People who have become resistant to tamoxifen may respond to this treatment.

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