Aromatase Inhibitor Reduces Breast Cancer Risk for Postmenopausal Women at High-Risk

ASCO Annual Meeting
June 4, 2011

A recent study showed that women who have been through menopause and have a high risk of breast cancer were less likely to develop the disease when they received an aromatase inhibitor (AI) called exemestane (Aromasin). An AI is a drug that reduces the amount of the hormone estrogen in a woman's body by stopping tissues and organs other than the ovaries from producing it. Previous research has shown that estrogen may help breast cancer grow. Drugs that block estrogen, such as tamoxifen (Nolvadex) and raloxifene (Evista), have been approved by the U.S. Food and Drug Administration to lower the risk of breast cancer for women at high risk for the disease. However, there is a risk of rare but serious side effects, such as uterine cancer and blood clots, with these two drugs. Researchers designed this study to find another option to lower breast cancer risk with fewer side effects. 

The 4,560 women who participated in this study had been through menopause and had at least one of the following risk factors for breast cancer: age of 60 or older, a five-year Gail risk score of 1.66% or higher (this means that out of a group of women with similar risk factors, 1.66% will develop breast cancer), a history of abnormal cells in the breast, or ductal carcinoma in situ (DCIS; a noninvasive cancer) that was treated with a mastectomy (removal of the breast).

After around three years, researchers found that the women who received exemestane were 65% less likely to develop invasive breast cancer. Also, the women taking exemestane were less likely to develop DCIS or abnormal cells in the breast. Menopausal symptoms, such as hot flashes, fatigue, sweating, sleeplessness, and joint pain were slightly more common for women who received exemestane.

What this means for patients

“The potential public health impact of these findings is important. World-wide it is estimated that 1.3 million women are diagnosed with breast cancer each year and nearly 500,000 women die of the disease. Results from this study indicate that exemestane is a promising new way to prevent breast cancer in menopausal women most commonly affected with breast cancer,” said Paul E. Goss, MBBCh, PhD, lead study author and Professor of Medicine at Harvard Medical School and Massachusetts General Hospital in Boston.

Questions to ask your doctor

  • What is my risk of breast cancer? What does this mean?
  • How is my risk determined?
  • If I'm at a high risk, are there steps I can take to reduce my risk?
  • Could you help me compare the benefits and risks of treatments to lower breast cancer risk?

For More Information

Guide to Breast Cancer


What to Know: ASCO's Guideline on Drugs to Lower Breast Cancer Risk