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Can Hormone Replacement Therapy Compromise a Mammogram's Accuracy?

From the WebMD Archives

Jan. 9, 2001 -- For some women, taking hormone replacement therapy after menopause may interfere with the ability of doctors to read their mammograms with accuracy and reliability.

Mounting evidence suggests that taking hormone replacement therapy, or HRT, in the form of estrogen alone or estrogen plus progestin, increases the thickness of breast tissue in some women who take the therapy for menopausal symptoms or to prevent osteoporosis.

Now a new study of 5,000 women appearing in the Jan. 10 issue of Journal of the American Medical Association shows that the thickening of the breast tissue occurs soon after starting HRT and continues for as long as the woman remains on the hormones. The findings are important because increased thickening of breast tissue can make it harder in some cases to accurately interpret mammograms, along with some other imaging tests.

However, the American Cancer Society's director of breast and cervical cancer says the study is not showing any evidence that the increased thickening, or density, of breast tissue increases the risk of cancer or is causing significant numbers of breast cancers to be missed on mammograms.

"A small decrease in accuracy of mammograms is not going to result in a huge increase in breast cancers," says Debbie Zaslow, PhD.

Marilyn Leitch, MD, a professor of surgery at the University of Texas Southwestern Medical Center in Dallas, tells WebMD the findings are not really surprising and should not be cause for alarm among women on HRT.

"It's an issue that people have been aware of," Leitch says. "It is true that density in breast tissue can make it harder to see things on a mammogram, but it doesn't make it impossible. This has been known for some time."

She says breast cancers, including very early cancers, are diagnosed by mammography in women on HRT all the time. She says most typically, women who have the densest breasts prior to HRT will have greater change than women with less dense breasts, and doctors need to keep that in mind. However, she says doctors also should reassure women who are concerned by this study that changes in density usually are normal and do not indicate an increased risk of cancer.

Still, she says women taking HRT or who are considering starting it should discuss the issue with their doctors.

Zaslow agrees. "Hopefully, her doctor or radiologist will let her know, and that is one more reason why she should get her mammogram every year."

The study's authors, led by Carolyn M. Rutter, PhD, say compared with women who did not take HRT, women who did were significantly more likely to have increases in the density of their breasts. The study also found differences in individual women's responses to HRT. For instance, the probability of an increase in tissue density while taking HRT increased with increasing age.

However, Rutter, a researcher with Group Health Cooperative's Center for Health Studies in Seattle, also found that women who stopped taking HRT during the study had decreases in breast tissue thickness, suggesting that the effect of HRT may be temporary and reversible.

A similar study presented last month at a radiology meeting by researchers from Germany found that HRT also compromises the accuracy of breast MRI scans, which are occasionally used after a woman has had a suspicious finding on a standard mammogram. The German researchers say the problem is so significant they believe women should actually consider stopping their hormone therapy a few weeks prior to having an MRI to reduce the risk of either missing a cancer that is hidden by increased breast tissue or detecting something that looks like a tumor but is only an increased mass of normal breast tissue.

But Zaslow says while the suggestion to stop HRT before having a breast scan may be reasonable in some cases under doctor supervision, it still needs to be studied further. For now, the women taking HRT should not stop therapy without talking first with their doctor to determine if the benefits of the therapy outweigh any potential risk.

"Women need to talk to their doctors about why they're taking HRT. If they're taking it for severe hot flashes and it's helping them, that may be more important than a slight possible decrease in their mammogram sensitivity," she says.

Stephen Taplin, MD, a co-author of the new study, agrees, saying in a press release that since there may be serious health risks associated with starting and stopping HRT, "it's too early to suggest that women stop taking the drug prior to their mammograms."