Postmenopausal women taking conjugated equine estrogen have about double the risk of developing benign proliferative breast disease, which is associated with increased breast cancer risk, compared with women taking placebo, researchers report in the April 16 issue of the Journal of the National Cancer Institute.

Thomas E. Rohan, M.D., Ph.D., from the Albert Einstein College of Medicine, Bronx, N.Y., and colleagues analyzed data from a trial of 10,739 postmenopausal women who were randomly assigned to 0.625 mg/day of conjugated equine estrogen or placebo.

After an average follow-up of 6.9 years, the researchers found 232 cases of benign proliferative breast disease, of which 155 cases were in the equine estrogen group and 77 were in the placebo group. The equine estrogen group had a higher risk of benign proliferative breast disease (hazard ratio 2.11), and benign proliferative disease without atypia (HR, 2.34) and with atypical hyperplasia (HR, 1.12).

"Use of 0.625 mg/d of conjugated equine estrogen was associated with a statistically significant increased risk of benign proliferative breast disease," Rohan and colleagues conclude.

Abstract
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