Tamoxifen Effectively Lowers Breast Cancer Risk in High-Risk Women Younger Than 55

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Research that analyzed the results of four large studies found that tamoxifen effectively reduces breast cancer risk in women younger than 55 who are at high risk. This benefit outweighed the costs and potential side effects of treatment. The research was published online in the journal Cancer.

Treating the women in the studies with tamoxifen for 5 years saved lives. The average life expectancy of high-risk women treated with tamoxifen was higher than the average life expectancy of high-risk women not treated with tamoxifen.

Tamoxifen is a SERM (selective estrogen receptor modulators) hormonal therapy medicine. Evista (chemical name: raloxifene) is also a SERM hormonal therapy medicine. (Evista wasn't evaluated in this study.) SERMs block the action of estrogen in breast and certain other cells by sitting in the cells' estrogen receptors. SERMs don't affect all estrogen receptors the same way because they're selective (as the name says). In bone cells, SERMs interact with the receptors the way estrogen does and strengthen bones. In breast cells, SERMs block the receptors' interaction with estrogen and limit cell growth.

Tamoxifen is used to:

  • reduce the risk of breast cancer in pre- and postmenopausal high-risk women
    • Results from the very large National Surgical Adjuvant Breast and Bowel Project study released in 1998 showed that treating high-risk women with tamoxifen reduced their overall invasive breast cancer risk by 50%.
  • reduce the risk of hormone-receptor-positive breast cancer coming back (recurring) when given after surgery and other treatments (radiation therapy, chemotherapy)
  • treat advanced-stage, hormone-receptor-positive breast cancer

Tamoxifen also can improve bone health in women taking it to treat breast cancer. Still, tamoxifen isn't approved by the U.S. Food and Drug Administration (FDA) to be used only to improve bone health.

Evista is used to:

  • strengthen bones in women with osteoporosis
  • reduce breast cancer risk in high-risk postmenopausal women
  • reduce breast cancer risk in postmenopausal women with osteoporosis

Results from the very large STAR (Study of Tamoxifen and Raloxifene) study showed that treating high-risk postmenopausal women with either Evista or tamoxifen reduced their breast cancer risk by 50%.

Both tamoxifen and Evista are FDA-approved to reduce breast cancer risk in high-risk postmenopausal women. Only tamoxifen is FDA-approved to reduce breast cancer risk in high-risk premenopausal women. Both tamoxifen and Evista are pills taken by mouth. Each is taken for 5 years to reduce breast cancer risk in high-risk postmenopausal women.

Postmenopausal women taking Evista to strengthen bones and reduce the risk of osteoporosis regardless of their breast cancer risk may take Evista for more than 5 years.

Because tamoxifen and Evista work in the same way, they have the same possible risks and side effects, including:

  • hot flashes
  • sweating
  • joint pain
  • leg cramps
  • flu-like symptoms
  • blood clots deep in the legs
  • a blood clot that travels to the lungs (called a pulmonary embolism)
  • stroke

The likelihood or severity of any side effect seems to be different for each medicine. One study found that women taking tamoxifen were more likely than women taking Evista to have bothersome hot flashes and sweating, while women taking Evista were more likely to have joint pain.

Because of the risk of potentially life-threatening blood clots, tamoxifen and Evista are NOT recommended for women who have had a serious blood clot or are at high risk for blood clots.

If you're a pre- or postmenopausal woman and your breast cancer risk is higher than average, talk to your doctor about your risk and the steps you can take to lower that risk. Your doctor can help you figure out your true risk and decide if medicine -- such as tamoxifen or Evista -- to lower your risk is appropriate for your unique situation. You and your doctor may use the National Cancer Institute's interactive risk calculator tool. This tool uses your personal and family medical history to objectively assess your breast cancer risk.

Editor's Note: In July 2013, the American Society of Clinical Oncology put out new guidelines on using hormonal therapy medicines to reduce breast cancer risk in high-risk undiagnosed women. Besides tamoxifen and Evista, the guidelines also recommend that doctors talk to postmenopausal high-risk women about using the aromatase inhibitor Aromasin (chemical name: exemestane) to reduce risk.

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