According to a report released by the Agency for Healthcare Research and Quality, four common and noninvasive tests for breast cancer are not accurate enough to replace biopsies for women with abnormal mammograms or physical examinations (http://effectivehealthcare.ahrq.gov/repFiles/BrCADx%20Final%20Report.pdf).
Because only one in five women undergoing biopsy following an abnormal mammogram or examination has breast cancer, noninvasive tests could reduce biopsies. However, this latest report indicates that four common noninvasive tests—magnetic resonance imaging, ultrasonography, positron emission tomography, and scintimammography—would miss 4% to 9% of cancer cases among women testing negative who have average risks for the disease.
Hampton T. Breast Cancer Tests. JAMA. 2006;295(12):1364. doi:10.1001/jama.295.12.1364-d