Magnetic resonance imaging detects more cancers in the opposite breast of women newly diagnosed with breast cancer than mammography plus clinical exam, according to an article in the March 29 issue of the New England Journal of Medicine.

The researchers found that magnetic resonance imaging scans of women who were diagnosed with cancer in one breast detected over 90 percent of cancers in the other breast that were missed by mammography and clinical breast exam at initial diagnosis.

Given the established rates of mammography and clinical breast exams for detecting cancer in the contralateral breast, adding an MRI scan to the diagnostic evaluation effectively doubled the number of cancers immediately found in these women.

The American College of Radiology Imaging Network (ACRIN) trial was designed to determine whether the use of MRI could improve on clinical breast exam and mammography in detecting breast cancer in the opposite breast at the time of initial breast cancer diagnosis.

Researchers recruited 1,007 women from 25 US institutions who had a recent diagnosis of cancer in one breast. A total of 969 women completed the study, which began in April 2003. All of the women enrolled had a negative mammogram and negative clinical breast exam of the opposite breast within 90 days prior to the MRI.

Of the 33 contralateral breast cancers diagnosed in the study, 30 cancers, or 91 percent, were diagnosed as a result of magnetic resonance imaging. Researchers found that the added benefit of scanning was consistent, regardless of a woman's cancer type, age, or breast density.

"One in ten women diagnosed with cancer in one breast will develop the disease in the opposite breast. Having a better technique to find these cancers as early as possible will increase the chances of successful treatment," said National Institutes of Health Director Elias A. Zerhouni, MD.

"We can now identify the vast majority of contralateral cancers at the time of a woman's initial breast cancer diagnosis," said Constance Lehman, MD, PhD, principal investigator of the ACRIN Breast MRI Trial, professor of radiology and director of breast imaging at the University of Washington and Seattle Cancer Care Alliance. "This means that instead of those women having another cancer diagnosis years after their initial treatment, we can diagnose and treat those opposite breast cancers at the time of the initial diagnosis."

Researchers are also hopeful that the strong ability of magnetic resonance imaging to predict the absence of a tumor will help some women avoid unnecessary mastectomies and provide them with more reassurance that the breast is disease free.

"Although no imaging tool is perfect, if the MRI is negative, the chance of cancer in that breast is extremely low. A potential outcome that we would be delighted to see is fewer unnecessary bilateral mastectomies," said Lehman.

Constantine Gatsonis, PhD, the study's statistician and director of Brown University's Center for Statistical Sciences, Providence, RI, said, "The size and scope of this study -- which followed nearly a thousand women receiving care in a variety of medical settings -- means that its findings are definitive and broadly applicable. Women can be assured that a negative MRI means that their chances of having a second cancer diagnosed within a year is miniscule."

For most women, the fear of a second cancer diagnosis is quite high. The researchers are hoping that breast MRI can improve a woman's quality of life both at the time of her diagnosis and later years.