Exemestane reduces likelihood of breast cancer in women at high risk

The aromatase inhibitor exemestane lowered the risk of breast cancer by 65% without severe side effects in a randomized, double-blind, placebo-controlled trial of 4,560 postmenopausal women at risk of the disease, researchers reported at the annual meeting of the American Society of Clinical Oncology in Chicago (June 4-8).

Their study, published online June 4 in the New England Journal of Medicine, randomly assigned the women to receive either exemestane or placebo. Their median age was 62.5 years; their median Gail risk score was 2.3% (chances in 100 of invasive breast cancer developing within 5 years).

At a median follow-up of 35 months, 11 women in the exemestane group and 32 in the placebo group had invasive breast cancers, with a 65% relative reduction in the annual incidence of invasive breast cancer. Women in the exesmestane cohort also had fewer precursor lesions (ductal and lobular carcinoma in situ and atypical ductal and lobular hyperplasia) and aggressive HER2-positive tumors than women in the placebo group.

In spite of some limitations to the study, including the relatively short 3-year median follow-up, “we found a favorable risk-to-benefit ratio with a strong preventive effect of exesmestane and … an excellent safety profile across a spectrum of women at average to high risk for breast cancer,” the authors write.

Adverse effects occurred in 88% of women taking exemestane compared with 85% of women taking placebo. The 2 groups showed no significant differences in fractures, cardiovascular events, other cancers, or treatment-related deaths, and minimal differences in quality-of-life scores.

The side effects of exemestane-slightly increased osteopenia, hot flashes, sweating, fatigue, and insomnia-are markedly less severe than those of tamoxifen, which include increased risk of uterine cancer, cataracts, and stroke.