High-Risk Women Often Don’t Take Risk-Reducing Medicines Because of Side Effects

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Both tamoxifen and Evista (chemical name: raloxifene) lower the risk of breast cancer in women at high risk for breast cancer. Still, a report written for the U.S. Preventive Services Task Force (USPSTF) says that many women don’t take the medicines because of side effects.

The report was published in the April 16, 2013 issue of the Annals of Internal Medicine. Read “Use of Medications to Reduce Risk for Primary Breast Cancer: A Systematic Review for the U.S. Preventive Services Task Force.”

Tamoxifen and Evista are hormonal therapy medicines called SERMs (selective estrogen receptor modulators). 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.

The USPSTF is a group of experts that makes recommendations to the U.S. Department of Health and Human Services on policies to prevent disease, including the best ways to reduce the risk of breast cancer.

The scientists who wrote the report for the USPSTF reviewed results from studies looking at how effective tamoxifen and Evista were at reducing the risk of breast cancer in high-risk women who had never been diagnosed with breast cancer.

They found that tamoxifen and Evista reduced the number of cases of invasive breast cancer by seven to nine cases in 1,000 women over 5 years compared to women who were taking a placebo (a sugar pill that looked just like tamoxifen or Evista). Tamoxifen seems to be a little better at reducing the risk of invasive breast cancer than Evista.

Still, tamoxifen may cause side effects, some of them serious, including:

  • blood clots
  • stroke
  • a higher risk of endometrial cancer
  • cataracts
  • leg cramps
  • weight gain
  • sweating
  • hot flashes
  • joint pain

While Evista also may cause blood clots and stroke, women taking Evista are less likely to have these two serious side effects compared to women taking tamoxifen. Evista also may cause:

  • hot flashes
  • sweating
  • joint pain
  • weight gain

In 2002, the USPSTF recommended that doctors offer women at high risk for breast cancer tamoxifen or Evista to reduce that risk. But the report noted that many women decide not to take the medicines because of the side effects. The report also said that more research is needed so doctors can better identify the women who would benefit most from taking tamoxifen or Evista to reduce breast cancer risk.

Right now, most doctors use some form of the Gail model, a standard breast cancer risk assessment tool. The Gail model assesses breast cancer risk based on a series of personal health questions that women and their doctors answer together. The questions ask about risk factors such as age, child-bearing history, family history of breast cancer, and breast biopsy results. The result is a Gail score, which estimates the risk of developing invasive breast cancer in the next 5 years. Some more recent versions of the Gail model also include alcohol use, menopausal status, and body mass index. Some doctors wonder if genetic testing or other information should be added to the Gail model. More research needs to be done to figure out the most accurate way to assess a woman’s risk of breast cancer.

If you have a higher-than-average risk of breast cancer, you already might be taking medicine to help keep your risk as low as it can be. If not, you may want to ask your doctor if taking a SERM – tamoxifen or Evista – makes sense for you. Besides lowering your breast cancer risk, each medicine has benefits and side effects. If taking a SERM makes sense for you, talk to your doctor about any side effects and how to manage them. Together, you can make the best choice for your unique situation.

You can learn more about tamoxifen and Evista in the SERMs pages of the Breastcancer.org Hormonal Therapy section.

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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