Study: MRIs can better detect cancer in women with dense breasts

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.

Sometimes those patients are advised to follow up by getting ultrasounds or magnetic resonance imaging, or MRI, scans, but for many, it is unclear what their next step should be.

Now, 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 advisory for DenseBreast-info.org, said the study’s finding 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.

“Women should be advocating for increased access to screening MRI,” she said.

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

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 suggests supplementary MRIs may be a lifesaving tool for women with dense breasts.