MRIs' breast-scan role focus of study

Test shows usefulness on dense tissue

Many women who have mammograms get normal results that come with a caveat: They are told they have dense breast tissue, which can make their scans harder to read and could leave cancer undetected.

A new study provides strong evidence that supplemental MRIs are more effective in finding tumors in these women than mammograms alone.

The study, of more than 40,000 women with extremely dense breasts in the Netherlands, found that those who had mammograms followed by MRIs had more tumors detected than with mammography alone. The research also found that those who had MRIs were less likely to find a cancerous lump in between routine screenings; by the time tumors are big enough to be felt, they tend to be more advanced.

The study, the first large randomized controlled trial of supplemental MRIs in women with dense breasts, was published in the New England Journal of Medicine on Wednesday.

Just under half of women over the age of 40 have dense breasts, which means their breasts have more connective and fibrous tissue than usual and relatively less fat. Women with dense breast tissue have a higher risk of developing breast cancer than women with more fatty breast tissue.

Dr. Wendie Berg, a professor of radiology at the University of Pittsburgh School of Medicine and chief scientific adviser for DenseBreast-info.org, said the study's findings were "very important."

"The standard practice of mammography alone is not adequate for women with extremely dense breasts," Berg said, adding that her own cancer was detected early enough to require minimal treatment because her family history led her to seek an MRI.

But though the study results were significant, it is still unclear whether supplementing mammograms with MRIs ultimately reduces breast cancer deaths.

"The ultimate test of the value of MRI screening" in these women will be "whether it improves survival -- an answer that we will not have for a very long time," cautioned Dr. Dan L. Longo, a deputy editor of the New England journal and professor of medicine at Harvard Medical School, in an editorial accompanying the study.

For all the promise, there is also a downside to using MRIs for breast cancer screening: They yield many false positive results that lead to unnecessary biopsies, and they can detect very early stage tumors that might never become life-threatening, said Carla van Gils, senior author of the study and a professor of clinical epidemiology at University Medical Center Utrecht.

Nevertheless, van Gils said, the significant reduction in interval cancers -- cancers that are diagnosed after a negative mammogram -- suggests supplementary MRIs may be a lifesaving tool for women with dense breasts.

Van Gils said the study is ongoing and that mathematical models will be run to make further predictions about mortality and overdiagnosis. "There are more questions that need to be answered."

A Section on 11/28/2019

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