Long-term treatment with conjugated equine estrogens (CEE) does not increase the risk of breast cancer in postmenopausal women who have had a prior hysterectomy, but it may increase the likelihood that mammographic screening results would require short-interval follow-up, according to the latest data from the Women's Health Initiative Estrogen-Alone trial.  

The 40-center trial, involving over 10,000 women between the ages of 50 and 79, compared 7 years of 0.625 mg/d CEE to placebo. The researchers calculated hazard ratios for invasive breast cancer and for ductal carcinomas for women assigned to CEE versus placebo to be 0.80 (95% CI; 0.62–1.04; 

=0.054), respectively. In other words, rates of breast cancer either did not differ significantly between the two groups or were actually slightly lower for certain subtypes of cancer in the treated arm.  

At 1 year, however, 9.2% of the women taking CEE had abnormalities on mammography that required follow-up versus 5.5% of the placebo group (

<0.001). By 7 years, 36.2% of the CEE group versus 28.1% of the placebo group required short-interval mammographic follow-up (

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Long-term treatment with conjugated equine estrogens (CEE) does not increase the risk of breast cancer in postmenopausal women who have had a prior hysterectomy, but it may increase the likelihood that mammographic screening results would require short-interval follow-up, according to the latest data from the Women's Health Initiative Estrogen-Alone trial.