By Anthony J. Brown, MD

MRI is more sensitive than mammography at detecting tumors in women with a familial or genetic predisposition to breast cancer, according to a report published in The New England Journal of Medicine for July 29th. The findings suggest that MRI be used in addition to mammography in this setting.

In the study, "MRI detected early, potentially curable cancers that in some cases were not picked up by mammography or physical exam," Dr. Laura Liberman, author of a related editorial, told Reuters Health. However, "MRI was a little less specific than mammography."

Despite the greater sensitivity seen with MRI, "I don't think this study suggests that MRI should be done instead of mammography," noted Dr. Liberman, from Memorial Sloan-Kettering Cancer Center in New York. "In this study, there were some cancers that were seen with mammography, but not with MRI. So, I think the use of MRI we are considering in the high-risk screening setting is as a supplement to mammography."

The findings stem from a study of 1909 women who were screened for breast cancer every 6 months with physical exam and every year with mammography and MRI. All of the women had a cumulative lifetime breast cancer risk of at least 15% and 358 were carriers of germ-line mutations. The characteristics of the cancers detected in this group were compared with those of two age-matched control groups.

During a median follow-up of 2.9 years, 44 invasive cancers, 6 ductal carcinomas in situ, 1 lobular carcinoma in situ, and 1 lymphoma were detected, senior author Dr. Jan G. M. Klijn, from Erasmus Medical Center in Rotterdam, the Netherlands, and colleagues report.

MRI was found to have a significantly better overall discriminating capacity than mammography (p < 0.05). The sensitivity for detecting invasive breast cancer ranged from 17.9% for physical exam and 33.3% for mammography to 79.5% for MRI. The corresponding specificities of the three procedures were 98.1%, 95.0% and 89.8%.

About 43% of invasive tumors detected in the screening group were no greater than 10 mm in diameter, the authors note. In contrast, only about 13% of tumors in the control groups were of this size (p < 0.05). Similarly, the proportion of invasive tumors with axillary disease or micrometastases was significantly smaller in the screening group.

In high-risk patients, "mammography only picks up about half of their cancers -- the other half pops up in the interval between screens," Dr. Liberman explained. "So, it has been suggested that supplementing mammography and clinical exam with some other ancillary test may improve cancer detection. That's, I think, where MRI comes in."

Dr. Liberman said that further studies are needed to determine who will benefit most from MRI screening and how to integrate this modality into mammographic screening.

N Engl J Med 2004; 351:427-437,497-500.

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