"Postmenopausal hormones make breasts denser—like young women's breasts—and make mammograms harder to 'read,'" explained Diana S.M. Buist, PhD, MPH, an associate investigator at Group Health Center for Health Studies in Seattle. This raises the chance of having a "false-positive." That means women are called back ("recalled") for more testing, only to learn they have no breast cancer after all.

"False-positives account for a quarter of the overall costs of mammography in the United States," Buist said. Previous evidence showed stopping hormones could improve mammography, which led some clinicians to suggest stopping briefly before a mammogram. But there was no evidence of how long women needed to stay off hormones for their mammograms to improve. "We thought it was important to see if stopping hormones for one or two months really did make any difference in clinical outcomes," she said. "And we also wanted to make sure that it didn't cause any harm."

It didn't work in practice, according to the READ trial. The trial's three groups did not differ significantly in what proportion was called back for more tests after screening mammography. Of the women (aged 45-80) who stayed on hormone therapy, 11.3% were called back for more tests, compared to 12.3% and 9.8%, respectively, of those who stayed off hormones for one or two months. Taking a break from hormone therapy was not without harm: increasing the women's menopause symptoms. But there was also some benefit—making their breasts slightly less dense.

What does breast density mean? Breast tissue is composed mainly of milk glands and fat. A breast is dense if it consists of more milk glands than fat. Dense breast tissue, like milk glands, is denser and looks white on an X-ray, making tumors harder to see. That's why any tumors are harder to detect on mammograms of denser breasts than on those of less dense breasts. Breast density tends to decline with age, but individual women differ in the density of their breasts. Aside from age, having dense breasts is the biggest risk factor for breast cancer.

"We really hoped to find that a brief break in hormone therapy would lower false-positives and remove unnecessary costs and anxiety by improving mammography," Buist said. "And we were disappointed to find that it didn't. But we'll keep trying to find ways to reduce recall rates for women—in hopes of making mammography more effective and ensuring women have to go through the least amount of testing and radiation that's necessary."

The READ trial is part of Group Health's ongoing research on the comparative effectiveness of tests, treatments, and preventive actions—and figuring out which ones work and which don't in real clinical settings. "These types of studies are being called for increasingly as America and policy makers think about how to reform our health care system," Buist said. "Studies like this are important for making sure that we are basing medicine on evidence and providing the most effective health care."

"This study does not change our clinical message to doctors or patients about hormone therapy," said Buist.

"After our trial, as before it, women should engage in shared decision making with their doctors about whether or not to take hormones for their menopause symptoms—and if so, for how long," added Buist's co-author Susan D. Reed, MD, MPH. "Even women who find hormone therapy helps their symptoms should reassess yearly whether to continue hormone therapy," added Reed, a professor of obstetrics and gynecology at the University of Washington and an affiliate investigator at Group Health Center for Health Studies.

The Department of Defense funded the READ trial, which enrolled women from Group Health's Breast Cancer Screening Program.

Buist and Reed's READ trial co-authors were Juleann C. Gandara, MD, of Group Health; and Katherine M. Newton, PhD; Erin J. Aiello Bowles, MPH; Melissa L. Anderson, MS; E. Dawn Fitzgibbons, MPH; and Deborah Seger of Group Health Center for Health Studies.

Note: If no author is given, the source is cited instead.

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