ROCKVILLE, MarylandBiopsy remains the gold standard for diagnosing breast cancer in women whose mammograms or physical exams yield abnormal findings, according to a new federal report. The four noninvasive tests most commonly used to assess breast cancer fail to provide the accuracy of biopsies and should not be used routinely as replacements, the study concluded. The American College of Radiology (ACR), however, took issue with the report, calling it "simplistic" and "misleading" (see box). Only about 20% of women who undergo a biopsy because of an abnormal mammogram or physical exam actually have breast cancer. For this reason, physicians and patient advocates have long hoped for a noninvasive technique to replace biopsy, which is painful, psychologically stressful, and carries some risk of adverse events. However, when researchers for the Agency for Healthcare Research and Quality (AHRQ) reviewed data on the four techniquesmagnetic resonance imaging (MRI), ultrasound, positron emission tomography (PET) scanning, and scintimammographythey found them wanting.
The report states that the four non-invasive tests would miss between 4% and 9% of breast cancers in women at average risk of the disease, and they could potentially miss a greater percentage of cancers in women at higher risk. For every 1,000 women who had a negative PET scan for breast cancer, the report concluded that 76 would have the disease. For MRI and ultrasound, the false negatives would number 38 and 50, respectively. For every 1,000 women with nonpalpable breast lesions who had negative scintimammograms, 93 would have cancer; the researcher team could not calculate a number for all lesions.
"If a less than 2% risk of having breast cancer with a negative diagnostic test is considered an acceptable level of risk for a diagnostic test to reliably preclude biopsy, none of these tests was sufficiently accurate to replace biopsy for women at average risk of breast cancer," the report said. "In general, the higher a woman's risk of cancer is before undergoing a noninvasive test, the higher is the risk that she has cancer even if the test is negative."
Findings from the report, Effectiveness of Noninvasive Diagnostic Tests for Breast Abnormalities, are based on a systematic review of 81 studies conducted by the ECRI Evidence-based Practice Center in Plymouth, Pennsylvania. The report noted that a potential confounding factor to the findings is the high prevalence of women with breast cancer enrolled in the studies reviewed: "This limitation reduces confidence that the results apply to all women who have suspicious mammograms" (see www.effectivehealthcare.ahrq.gov/reportsfinal.cfm).