In a study in which pathologists provided diagnostic interpretation of breast biopsy slides, overall agreement between the individual pathologists’ interpretations and that of an expert consensus panel was 75%.

The highest level of concordance occurred for invasive breast cancer and lower levels of concordance occurred for ductal carcinoma in situ (DCIS) and atypical hyperplasia (atypia). This study was published in JAMA (2015; doi:10.1001/jama.2015.1405).

Approximately 1.6 million women in the United States undergo breast biopsy each year. The accuracy of pathologists’ diagnoses is an important and inadequately studied area. Although nearly one-quarter of biopsies demonstrate invasive breast cancer, pathologists categorize most biopsies according to a diagnostic spectrum ranging from benign to pre-invasive disease.

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Breast lesions with atypia or ductal carcinoma in situ (abnormal breast cells that have not spread outside the duct into the surrounding breast tissue) are associated with significantly higher risks of subsequent invasive carcinoma, and women with these findings may require additional surveillance, prevention, or treatment to reduce their risks. The incidence of atypical ductal hyperplasia (a benign lesion of the breast that indicates an increased risk of breast cancer) and DCIS breast lesions has increased over the past three decades as a result of widespread mammography screening.

Misclassification of breast lesions may contribute to either overtreatment or undertreatment, according to background information in the article.

Joann G. Elmore, MD, MPH, of the University of Washington in Seattle, and colleagues 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 US 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 cases of DCIS, 72 cases of atypia, and 72 benign cases without atypia.

Participants were blinded to the interpretations of other study pathologists and the three consensus panel members, who were experienced pathologists internationally recognized for research and continuing medical education on diagnostic breast pathology.

Among the consensus panel members, unanimous agreement of their independent diagnoses was 75%, and concordance with the consensus-derived reference diagnoses was 90%.

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%.

Although overinterpretation of DCIS as invasive carcinoma occurred in only 3% of cases, overinterpretation of atypia was noted in 17%, and overinterpretation of benign without atypia was noted in 13%. Underinterpretation of invasive breast cancer was noted in 4% of cases, whereas underinterpretation of DCIS was noted in 13%, and underinterpretation of atypia was noted in 35%.

A related editorial (doi:10.1001/jama.2015.1945) stated that these findings will undoubtedly heighten the anxiety of women and their physicians about the accuracy of the pathologic diagnosis. However, the study confirmed that the majority of diagnoses, especially at the ends of the spectrum from benign to invasive cancer, are accurate.