The results contrast with the previously reported WHI Estrogen plus Progestin Trial, which found an increase in breast cancer over about 5 years among those taking combined hormone therapy.
The WHI is sponsored by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health. The new analysis is published in the April 12 issue of the Journal of the American Medical Association. Over an average of about 7 years of follow-up, study participants taking estrogen had fewer breast cancer tumors than those in the placebo group. Women in the estrogen group were diagnosed with breast cancer at a rate of 28 per 10,000 participants per year versus a rate of 34 per 10,000 participants per year in the placebo group. The difference in rates of breast cancer (6 per 10,000) between the groups was not statistically significant, meaning it could have occurred by chance.
The new analysis also found that participants taking estrogen had 50 percent more abnormal mammograms that required follow-up and underwent 33 percent (747 compared to 549) more breast biopsies. An abnormal mammogram does not necessarily signal cancer as shown in this study's results.
"Longer follow-up is needed to fully explain the reduced number of breast cancers in women taking estrogen. However, this new analysis does not alter the overall conclusion from the WHI that hormones, including estrogen-alone and estrogen plus progestin, should not be used for the prevention of chronic disease," said NHLBI Director and WHI Director Elizabeth G. Nabel, M.D. "The findings still support current recommendations that hormone therapy should only be used to treat menopausal symptoms and should be used at the smallest effective dose for t
Contact: NHLBI Communications Office
NIH/National Heart, Lung, and Blood Institute