Key clinical point: Prior use of conjugated equine estrogen in women who had a hysterectomy was associated with lower breast cancer incidence and mortality.

Major finding: Conjugated equine estrogen alone was associated with lower mortality (30 deaths, annualized mortality rate 0.031%), compared with placebo (46 deaths, annualized mortality rate 0.046%); HR 0.60; 95% CI, 0.37-0.97; P = .04.

Study details: This was a long-term follow-up study of two Women’s Health Initiative clinical trials of postmenopausal women with no prior breast cancer.

Disclosures: The Women’s Health Initiative is supported by the National Heart, Lung, and Blood Institute, the National Institutes of Health, and the Department of Health and Human Services. The authors reported numerous potential conflicts of interest, including receiving personal fees and grants from various government organizations, foundations, and pharmaceutical companies.