Breast Health Program

Hormonal therapy

Blocking the effects of estrogen on the body in women and men with estrogen receptor positive breast cancer is one of the mainstays to treatment and prevention of systemic breast cancer. Two classes of medications we use routinely are selective estrogen receptor modulators, or SERMs, and aromatase inhibitors, or AIs.,

Selective estrogen receptor modulators

The best-known SERM is Tamoxifen or Nolvadex®. Tamoxifen works against the effects of estrogen on these cells. It is often called an antiestrogen. This drug, taken by mouth, blocks the activity of estrogen, a female hormone. Estrogen can stimulate the development of cancer cells in the breast. Tamoxifen is approved by the U.S. Food and Drug Administration, or FDA, for breast cancer prevention and treatment. It has been used for more than 30 years in women and men. 

Tamoxifen is given in early stage breast cancer for five years or until a patient is switched to an aromatase inhibitor. It is also used when the breast cancer has spread elsewhere in the body. Tamoxifen helps prevent the original breast cancer from returning and also helps prevent the development of new cancers in the other breast. As treatment for metastatic breast cancer, the drug slows or stops the growth of cancer.

Tamoxifen has been used for almost 10 years to reduce the risk of breast cancer in women who are at increased risk of developing breast cancer.


  • Blood clots
  • Strokes
  • Uterine cancer
  • Cataracts
  • Symptoms of menopause, including hot flashes, vaginal discharge, irregular periods, headaches, fatigue, nausea, vaginal dryness, decrease in sexual interest

For more information visit The National Cancer Institute.

Aromatase inhibitors

Aromatase inhibitors are a class of anticancer drugs used to decrease estrogen production and suppress the growth of tumors that need estrogen to grow. They work by blocking androgens, an enzyme aromatase in the adrenal gland that produces estrogen from fat substrates. This means less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells.

Aromatase inhibitors can’t stop the ovaries from making estrogen, so aromatase inhibitors only work in post-menopausal women.

There are three aromatase inhibitors:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

Each is a pill, usually taken once a day.

Benefits of aromatase inhibitors

Several studies have compared aromatase inhibitors with tamoxifen to see which type of medicine was more effective in treating early-stage, hormone-receptor-positive breast cancer in post-menopausal women. Based on the results, most doctors agree on the following after initial treatment (surgery and possibly chemotherapy and radiation therapy):

  • An aromatase inhibitor is the best hormonal therapy to start with. When treating early-stage, hormone-receptor-positive breast cancer, aromatase inhibitors have more benefits and fewer serious side effects than Tamoxifen.
  • Switching to an aromatase inhibitor after taking tamoxifen for two to three years (for a total of five years of hormonal therapy) offers more benefits than five years of Tamoxifen.
  • Taking an aromatase inhibitor for five years after taking Tamoxifen for five years continues to reduce the risk of the cancer coming back, compared to no treatment after Tamoxifen.

Side effects of aromatase inhibitors

Aromatase inhibitors tend to cause fewer serious side effects than Tamoxifen; however, side effects include:

  • Cardiac problems.
  • Bone loss/osteoporosis.
  • Broken bones.
  • Joint stiffness.
  • Joint pain.

If you and your doctor are considering an aromatase inhibitor as part of your treatment plan, you may want to ask your doctor about having a bone density test to see if a bone strengthening medicine might be necessary while you’re taking the aromatase inhibitor.

If you’re experiencing side effects from taking one aromatase inhibitor medicine, tell your doctor. You may be able to take a different medicine. Arimidex and Femara have similar chemical structures, while Aromasin has a different structure.

Ask your doctor if you have specific question regarding hormone therapy.


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