Reproducibility of histological diagnosis of breast lesions: results of a panel in Italy.

Sixteen pathologists independently examined and classified a series of 81 breast lesions selected from the files of several Italian Pathology Departments in the context of a national task force on breast cancer (FONCAM). A four category classification system was used for analysis; according to the majority diagnosis (MD), simply defined as the most frequently reported in the panel, the series included 37 benign lesions without atypia (45.7%), nine atypical hyperplasias (11.1%), 18 in situ (22.2%) and 17 invasive carcinomas (21.0%). Concordance, estimated for all possible pair-wise comparisons between pathologists, was good (mean kappa value: 0.59). A comparison between the diagnoses of each pathologist and the panel majority diagnosis was also made. Overall, a global kappa value of 0.72 was found (range 0.57-0.85), with category-specific values being excellent for invasive carcinoma (0.89) and benign lesions without atypia (0.77), relatively good for in situ carcinoma (0.69) but poor for atypical hyperplasia (0.38). These results confirm that quality assurance procedures are particularly indicated for large screening programmes for breast cancer, and suggest that for atypical lesions strict diagnostic criteria should be adopted.