Hormone Therapy Increases Frequency of Abnormal Mammograms and Breast Biopsies

February 2008

Findings Summary

Combined estrogen plus progestin hormone therapy appears to increase the risk that women will have abnormal mammograms and breast biopsies, and may decrease the effectiveness of both tests for detecting breast cancer, according to a report in the February 25, 2008 issue of Archives of Internal Medicine.
Rowan T. Chlebowski, M.D., Ph.D., principal investigator of the Harbor–UCLA WHI Clinical Center, and other investigators have published new findings from the WHI Estrogen plus Progestin (E+P) Hormone Trial. Of the 16,608 women enrolled in the E+P Trial, 8,506 were randomly assigned to take active study pills with combined estrogen plus progestin, while 8,102 took inactive placebo pills. Each woman had a mammogram and breast examination yearly. Biopsies were performed based on their physicians’ clinical judgment.
During the 5.6 years of the trial, 199 women in the active hormone group and 150 women in the placebo group developed breast cancer. Mammograms showing abnormal results were more common among women taking hormones than among women taking placebo (35% vs. 23%). In fact, women taking hormones had a 4% greater risk of having a mammogram with abnormalities after just one year of starting the hormones and an 11% greater risk after five years. After the hormones were stopped, the adverse effect on mammograms decreased somewhat, but remained significantly different from that of placebo for at least 12 months after stopping, the investigators reported.
Breast biopsies also were more common among women taking hormones than among those taking placebo (10% vs. 6.1%). “Although breast cancers were significantly increased and were diagnosed at higher stages in the combined hormone group, biopsies in that group less frequently diagnosed cancer (14.8% vs. 19.6%),” the WHI investigators reported.
These findings suggest that mammograms and breast biopsies may be more difficult to interpret for women taking hormones. Thus, the hormone pills compromised the diagnostic performance of both. The investigators recommend that health care providers include this information when they discuss risks and benefits with women who are thinking about taking even short-term combined hormone therapy.