(HealthDay News) – The use of estrogen-only after hysterectomy lowers the risk of breast cancer, but largely in groups already at low risk of breast cancer, according to a study published online March 7 in The Lancet Oncology.

Garnet L. Anderson, PhD, from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues analyzed data on breast cancer incidence from 7,645 postmenopausal women who had undergone a hysterectomy and had been randomly assigned to receive placebo or oral conjugated equine estrogen. The women had been taking estrogen for a median of 5.9 years and were followed for a median of 11.8 years. The authors note that the trial was terminated early due to an increased risk of stroke and blood clots.

The researchers found that the estrogen group had a significantly lower incidence of breast cancer (0.27% vs. 0.35% per year; hazard ratio [HR], 0.77; P=0.02). The lower risk was largely confined to women without benign breast disease or without a family history of breast cancer. Compared with controls, fewer women in the estrogen group died of breast cancer (HR, 0.37; P=0.03) or from any cause after a breast cancer diagnosis (HR, 0.62; P=0.04).

“Although breast cancer incidence and related mortality were lower for women who took estrogen alone than for controls, our findings do not support estrogen use for breast cancer risk reduction because subgroup analyses suggest the benefit might not apply to populations at increased breast cancer risk,” Anderson and colleagues conclude.

The study was funded by Wyeth. One author disclosed financial and consulting relationships with several pharmaceutical companies.

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