What can you tell me about a new treatment to prevent breast cancer from coming back?

You may be referring to an anti-estrogen drug called exemestane. This drug has been in the news recently because of the encouraging results of a major research study.

The hormone estrogen promotes the growth of some types of breast cancer cells. Doctors prescribe anti-estrogen drugs to deprive the cancer cells of estrogen. For many years, the most widely used anti-estrogen drug was tamoxifen. Now, a large international study has found that taking exemestane after several years of taking tamoxifen is more effective than continuing with tamoxifen alone in preventing breast cancer from returning.

The London-based study involved almost 5,000 women past menopause. The women had the type of breast cancer that grows with the help of estrogen. All were cancer-free after taking tamoxifen for two or three years following surgery. The women were divided into two groups. One group continued taking tamoxifen, and the other group switched to exemestane.

Tamoxifen and exemestane both act against the effects of estrogen in breast tissue, but they work in different ways. Tamoxifen limits the ability of estrogen to help the cancer grow. Exemestane blocks the body's ability to make estrogen in the first place.

After three years, 91.5 percent of the women who took tamoxifen followed by exemestane were free of cancer, compared with 86.8 percent of women in the tamoxifen-only group. These findings confirmed several earlier studies suggesting that exemestane increases the chance of remaining cancer-free after breast cancer treatment in women who have gone through menopause.

However, researchers note that more research is needed to understand the long-term effectiveness and possible side effects of exemestane. For example, studies have suggested that the drug may increase the risk of bone loss and fractures.

Exemestane is not appropriate for women who have not gone through menopause. It also may not be appropriate for women who are at high risk for bone fractures. For more information, talk with your doctor or call the Cancer Information Service at 800-4-CANCER.

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