Conjugated equine estrogen alone increased postmenopausal breast cancer detection by mammogram

The use of conjugated equine estrogen alone for five years significantly increased mammograms with short-interval follow-up recommendations in postmenopausal women, but not mammograms with more serious findings, according to a new analysis of the Women’s Health Initiative.

“These findings differ from estrogen plus progestin use, for which significantly increased abnormal mammograms and a compromise in breast cancer detection are seen,” the researchers wrote.

The researchers assessed the influence of conjugated equine estrogen therapy alone on breast cancer detection in 10,739 postmenopausal women with prior hysterectomy included in the Women’s Health Initiative. Women were randomly assigned conjugated equine estrogen (0.625 mg/per day) or placebo. Breast exams and mammography were performed at baseline and annually.

During a mean 7.1 years of follow-up, fewer invasive breast cancers were identified in women assigned conjugated equine estrogen compared with placebo; however, this finding was not statistically significant. Women assigned conjugated equine estrogen also had fewer invasive breast cancers diagnosed with tumors 2 cm or less vs. placebo (P=.008).

Conjugated equine estrogen use alone increased mammograms with short-interval follow-up recommendations (39.2% vs. 29.6%; P<.001) but did not increase abnormal mammograms, such as those suggestive of malignancy (7.3% vs. 7%; P=.41).

Breast biopsies were more common among women assigned conjugated equine estrogen vs. placebo (12.5% vs. 10.7%; P=.004). These biopsies were also less commonly diagnosed as cancer (8.9% vs. 15.8% for positive biopsies; P=.04).

Breast cancer detection using mammogram was significantly compromised only in the early years of use among women assigned conjugated equine estrogen alone.

“Conjugated equine estrogen alone use for five years results in approximately one in 11 and one in 50 women having otherwise avoidable mammograms with short-interval follow-up recommendations or breast biopsies,” the researchers wrote.

Chlebowski RT. J Clin Oncol. 2010;152:doi:10.1200/JCO.2009.24.8799.