Diagnostic Accuracy of Pathologists Interpreting Breast Biopsies Examined

The pathological diagnosis of a breast biopsy is usually considered the gold standard for patient management and clinical outcomes; however, a continuum of histologic features exists from benign to atypical to malignant on which diagnostic boundaries are imposed.

A team of North American scientists led by the University of Washington School of Medicine (Seattle, WA; USA) examined the extent of diagnostic disagreement among pathologists compared with a consensus panel reference diagnosis. The study included 115 pathologists who interpret breast biopsies in clinical practices in eight USA states. Participants independently interpreted slides between November 2011 and May 2014 from test sets of 60 breast biopsies (240 total cases, one slide per case), including 23 cases of invasive breast cancer, 73 ductal carcinoma in situ (DCIS), 72 with atypical hyperplasia (atypia), and 72 benign cases without atypia.

For all the cases, the participants provided 6,900 total individual interpretations for comparison with the consensus-derived reference diagnoses. Participating pathologists agreed with the consensus panel diagnosis for 75% of the interpretations. The overall concordance rate for the invasive breast cancer cases was 96%. The participants agreed with the consensus-derived reference diagnosis on less than half of the atypia cases, with a concordance rate of 48%. The overall concordance rate for benign without atypia was 87%; for DCIS, it was 84%. Among the consensus panel members, unanimous agreement of their independent diagnoses was 75%, and concordance with the consensus-derived reference diagnoses was 90%.

Although over interpretation of DCIS as invasive carcinoma occurred in only 3%, over interpretation of atypia was noted in 17% and over interpretation of benign without atypia was noted in 13%. Under interpretation of invasive breast cancer was noted in 4%, whereas under interpretation of DCIS was noted in 13% and under interpretation of atypia was noted in 35%. Disagreement with the consensus-derived reference diagnosis was significantly more frequent when breast biopsies were interpreted by pathologists with lower weekly case volume, from non-academic settings, or smaller practices; and from women with dense breast tissue on mammography versus low density.

The authors concluded that the variability of pathology interpretations is relevant to concerns about overdiagnosis of atypia and DCIS. When a biopsy is over interpreted (e.g., interpreted as DCIS by a pathologist when the consensus-derived reference diagnosis is atypia), a woman may undergo unnecessary surgery, radiation, or hormonal therapy. In addition, over interpretation of atypia in a biopsy with otherwise benign findings can result in unnecessary heightened surveillance, clinical intervention, costs, and anxiety. The study was published on March 17, 2015, in the Journal of the American Medical Association.

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University of Washington School of Medicine