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Breast Cancer Health Center

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Can Hormone Replacement Therapy Compromise a Mammogram's Accuracy?

WebMD Health News

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.

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