Harvard Health Letter

Preventing cancer: Are we getting closer?

A breast cancer drug raises hope for chemoprevention.

One major story that came out of the American Society of Clinical Oncology (ASCO) meeting in June 2011 focused on a study of a drug called exemestane (pronounced ex-ee-MESS-tane). Exemestane is in a class of drugs called aromatase inhibitors, which women take for several years after they've been treated for breast cancer to reduce the chances of getting breast cancer again. Aromatase is an enzyme that's crucial to the production of the hormone estrogen, which in many cases fuels the development and growth of breast cancer. So by inhibiting aromatase, exemestane lowers estrogen levels and therefore the risk of breast cancer recurrence.

The results reported at the ASCO meeting (and published simultaneously in The New England Journal of Medicine) were from a study testing whether exemestane might be able to prevent invasive breast cancer. The 4,560 postmenopausal women (average age, 62.5) who volunteered to be in the study had never had invasive breast cancer, although they did, for various reasons, including their age, have a higher-than-normal risk for getting it in the future. Half the women took exemestane daily; the other half, a placebo. After three years, 11 (0.5%) of the 2,285 women who took exemestane had developed invasive breast cancer, compared with 32 (1.4%) of the 2,275 women who took a placebo.

The researchers who conducted the study calculated that 94 women would need to take exemestane for three years to prevent one case of breast cancer. Pfizer, which makes Aromasin, the brand-name version of exemestane (it's also available as a generic), funded the study.

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