Consistency achieved by 23 European pathologists from 12 countries in diagnosing breast disease and reporting prognostic features of carcinomas

A detailed analysis of the consistency with which pathologists from 12 diff erent European countries diagnose and classify breast disease was undertake n as part of the quality assurance programme of the European Breast Screeni ng Pilot Network funded by the Europe against Cancer Programme. Altogether 107 cases were examined by 23 pathologists in 4 rounds. Kappa (kappa) stati stics for major diagnostic categories were: benign (not otherwise specified ) 0.74, atypical ductal hyperplasia (ADH) 0.27, ductal carcinoma in situ (D CIS) 0.87 and invasive carcinoma 0.94. ADH was the majority diagnosis in on ly 2 cases but was diagnosed by at least 2 participants in another 14, in 9 of which the majority diagnosis was benign (explaining the relatively low kappa for this category), DCIS in 4 (all low nuclear grade) and invasive ca rcinoma (a solitary 1-mm focus) in 1. The histological features of these ca ses were extremely variable; although one feature that nearly all shared wa s the presence of cells with small, uniform, hyperchromatic nuclei and a hi gh nucleo-cytoplasmic ratio. The majority diagnosis was DCIS in 33 cases; k appa for classifying by nuclear grade was 0.38 using three categories and 0 .46 when only two thigh and other) were used. When ADH was included with lo w nuclear grade DCIS there was only a slight improvement in kappa. Size mea surement of DCIS was less consistent than that of invasive carcinoma. The m ajority diagnosis was invasive carcinoma in 57 cases, the size of the major ity being 100% in 49. The remainder were either special subtypes (adenoid c ystic, tubular, colloid, secretory, ductal/medullary) or possible microinva sive carcinomas. Subtyping was most consistent for mucinous (kappa, 0.92) a nd least consistent for medullary carcinomas (kappa, 0.56). Consistency of grading using the Nottingham method was moderate (kappa=0.53) and consisten cy of diagnosing vascular invasion, fair (kappa=0.38). There was no tendenc y for consistency to improve from one round to the next, suggesting that fu rther improvements are unlikely without changes in guidelines or methodolog y.