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Diagnostic Mammograms: Interpretation Is in the Eye of the Beholder

Sensitivity and false-positive rates varied among radiologists’ interpretations of diagnostic mammograms.

Radiologists’ interpretations of screening mammograms are known to vary widely. In a National Cancer Institute–funded study, investigators assessed the performance of 123 radiologists in their interpretations of more than 35,000 diagnostic mammograms in women with signs or symptoms of breast cancer. Mammograms were considered positive if they were suspicious or highly suggestive of cancer or if they prompted recommendation for biopsy or surgical consultation. Women were considered to have breast cancer if invasive carcinoma or ductal carcinoma in situ was diagnosed within 1 year of the diagnostic mammogram. Sensitivity was defined as the percentage of positive examinations among women with a breast cancer diagnosis. The false-positive rate was defined as the percentage of positive examinations among women without a breast cancer diagnosis.

Approximately three quarters of the radiologists (mean age, 49; range, 34–70) had been interpreting mammograms for at least 10 years. Only 6% were based at academic centers; 3% had fellowship training in breast imaging. For most (87%), less than 40% of their time was devoted to breast imaging. The median sensitivity of diagnostic mammography was 79%, and the median false-positive rate was 4.3%. Sensitivity varied substantially even among radiologists with similar false-positive rates. Radiologists at academic centers had higher interpretive sensitivity (88% vs. 76%) and higher false-positive rates (7.8% vs. 4.2%) than did other radiologists.

Comment: The prevalence of breast cancer is 10-fold higher in women undergoing diagnostic mammography than in women undergoing screening breast imaging. Accordingly, the variability in radiologists’ interpretations of diagnostic mammograms is worrisome. Although high sensitivity expedites breast cancer diagnosis, the rate of false-positive interpretations (which generate invasive procedures and anxiety) tends to increase with sensitivity. Therefore, achieving optimal accuracy — high sensitivity without excessive false-positives — is critical in interpreting diagnostic mammograms. General radiologists read most of the mammograms in the U.S., yet breast imaging constitutes a relatively small part of their practices. These results point to the variability among radiologists; from here, we must determine how best to improve accuracy in the interpretation of diagnostic mammograms.

— Andrew M. Kaunitz, MD

Published in Journal Watch Women's Health January 10, 2008

Citation(s):

Miglioretti DL et al. Radiologist characteristics associated with interpretive performance of diagnostic mammography. J Natl Cancer Inst 2007 Dec 19; 99:1854.

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