NEW YORK — Breast MRI may have difficulty keeping up with the “potentially logarithmic demand” for its use as a cancer screening tool, experts said at a cancer symposium sponsored by New York University and by the Lynne Cohen Foundation for Ovarian Cancer Research.
The technique represents a vast improvement in sensitivity over traditional mammography and ultrasound, but it “may have been oversold” as a screening tool, said Linda Moy, M.D., of the university.
“MRI isn't suitable for use as an annual cancer screening tool for most women,” she said, noting that it is too expensive (at about 10 times the cost of a mammogram) and too time consuming (at about 45 minutes per exam) to replace the more than 30 million screening mammograms performed annually.
But MRI remains the most promising of all breast screening modalities for one group of patients: BRCA mutation carriers. “MRI is the clear winner in every screening study undertaken to date in high-risk women,” said Ellen Warner, M.D., of the University of Toronto.
In six large, prospective, nonrandomized studies that have compared screening tools for high-risk women, MRI's sensitivity was considerably higher than that of mammography, with ultrasound and clinical breast exam trailing far behind. Overall, Dr. Moy noted, most studies have found a sensitivity rate of 86%–100% for MRI in high-risk women, with reported sensitivities of only 33%–55% for mammography.
“This stands in sharp contrast to the excellent sensitivity of screening mammography for detecting [ductal carcinoma in situ] and early invasive breast cancers in the general population,” Dr. Warner said. The difference, in part, can be attributed to the younger age—and greater average breast density—at which mutation carriers present for screening; MRI is far less influenced by breast density than is mammography.
But while MRI is the undisputed sensitivity champion for screening high-risk women, it does have its drawbacks. First, it's not nearly as specific as it is sensitive. In the Dutch National Study, which followed 1,909 women, including 358 mutation carriers, MRI had a recall rate double that of mammography (10% vs. 5%), and triple the biopsy rate (5.8% vs 1.7%).
“The price of MRI's greater sensitivity is more false positives,” Dr. Warner said. “MRI researchers are now working on protocols that we hope will slash recall and biopsy rates.”
And no one yet knows whether MRI is actually saving women's lives. “To date, no study has proved that any screening regimen can actually increase survival rates,” she said.
“If MRI is picking up cancers prior to distant metastasis that would have gone undetected until after metastasis with other screening tools, then it will have a favorable impact on survival. But we don't know that yet,” Dr. Warner added.
At left, MRI without contrast hints at a mass near the nipple. At right, the mass that is seen on high-contrast MRI was found to be invasive ductal carcinoma.
The invasive ductal cancer present in the patient's right breast is not visible in a craniocaudal (CC) mammogram or a mediolateral oblique (MLO) mammogram. Photos courtesy Dr. Linda Moy
