MRI Detects Breast Cancer Missed by Mammography in High-Risk Women

By Serena Gordon
HealthDay Reporter
Monday, May 7, 2007; 12:00 AM

WEDNESDAY, March 28 (HealthDay News) -- Women who have already been diagnosed with breast cancer should have a magnetic resonance imaging (MRI) scan of the other breast in addition to mammography. Doing so may help doctors find a small number of cancer cases missed by mammography, a new study reports.

The study found that MRI scans picked up 3 percent of cancers missed by mammography alone in women who had already been diagnosed with cancer in one breast.

"The results of this study will lead to changes in practice," said Dr. Etta Pisano, one of the study's authors, and director of the Biomedical Research Imaging Center at the University of North Carolina at Chapel Hill School of Medicine. "While this study does not suggest that MRI supplants mammography, I think what will end up happening is that all women with breast cancer will end up getting MRI" if they've had a normal mammography.

In fact, the American Cancer Society issued new guidelines Wednesday that recommend an annual MRI screen in addition to an annual mammography for women at high risk of breast cancer.

But, because the false-positive rate of MRIs was relatively high -- about 11 percent in the new study -- the authors don't recommend MRI as a screening tool for the general population.

For the new study, Pisano and her colleagues performed MRI scans on 969 women who had recently been diagnosed with breast cancer in one breast. Mammography did not detect abnormalities in the other breast of the women.

One hundred and twenty-one women had positive MRI findings, meaning they had suspected cancer in the other breast. Biopsies were done to confirm the cancer diagnosis.

Of those women, 30 were found to have cancer in the second breast -- cancers that hadn't been detected with mammography.

But, the test wasn't perfect. It had a false-positive rate of 10.9 percent.

"The costs of false-positives have to be weighed against the cost of missing a cancer," explained Pisano, adding that for women who've already been diagnosed with breast cancer, the additional knowledge gained from the MRI outweighs the false-positive risk.

"For these women, because they're at such high-risk, everything is worrisome. You really want to know that you're going to give them cancer therapy once, rather than twice," she said.

The results are published in the March 29 issue of theNew England Journal of Medicine.

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