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MRI Better Detects Breast Cancers in High-Risk Groups


 

CHICAGO — Magnetic resonance imaging detects more breast cancers than mammography in high-risk women, according to the first international study comparing the two screening methods.

“Our results support the benefit of MRI screening, not as a replacement, but as a complement to mammography in high-risk women,” said Constance D. Lehman, M.D., lead investigator of the International Breast Magnetic Resonance Consortium Trial. She presented the findings at the annual meeting of the Radiological Society of North America.

The study included 367 women aged 25 and older, with a mean age of 45, from 13 sites. The women were considered to be at high risk for breast cancer, with at least a 25% lifetime risk. They underwent a clinical breast exam, mammography, and MRI, within a 90-day period.

In 90% of the study population, the mammogram and MRI findings agreed. A total of 329 women had negative findings on both tests, and 1 woman had positive findings on both tests, resulting in a biopsy and detection of a cancer.

However, 8% (30 women) had negative mammograms but positive findings on MRI. Of these women, 23 had biopsies, and 3 cancers were detected.

In addition, 2% (or seven of the women) had positive mammograms but negative MRI findings. Of these, three had biopsies, and no cancers were detected.

Four cancers were detected in the study cohort—three infiltrating ductal carcinomas and one ductal carcinoma in situ—for a rate of 1.1% and a benign biopsy rate of 5%.

Although MRI alone had a diagnostic yield of 1.1%, meaning it could detect 11 cancers in 1,000 high risk women, the diagnostic yield of mammography alone was 0.3%, meaning it could detect only 3 cancers in this same group.

Although three of the four cancers were in women who had negative mammograms but positive MRIs, this does not weaken the value of mammograms, Dr. Lehman said.

“We're trying to encourage physicians not to trust a negative mammogram and thus rule out the need for a biopsy in this population,” she said at a press briefing. “But we are also not at the point where a negative MRI can overrule a positive mammogram. If we see calcification on a mammogram, there is a significant risk of cancer, even when the MRI is negative,” said Dr. Lehman, director of breast imaging at the University of Washington, Seattle.

Dr. Lehman said there is no evidence that the benefits of combining MRI and mammography apply to the general population, in whom mammography performs well. But mammography is not optimal in younger women, who tend to have dense breast tissue—and high-risk women need to begin regular screening when they are young.

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