Causes of inconsistency in diagnosing and classifying intraductal proliferations of the breast

It is now widely recognised that classifying ductal carcinoma in situ (DCIS ) of the breast and diagnosing atypical ductal hyperplasia are associated w ith significant interobserver variation. Two possible reasons for this inco nsistency are differences in the interpretation of specified histological f eatures and field selection where morphology is heterogeneous. In order to investigate the relative contribution of these two factors to inconsistent interpretation of intraductal proliferations, histological sections of 32 l esions were sent to 23 European pathologists followed 3 years later by imag es of small parts of these sections. Kappa statistics for diagnosing hyperp lasia of usual type, atypical ductal hyperplasia and ductal carcinoma in si tu were 0.54, 0.35 and 0.78 for sections and 0.47. 0.29 and 0.78 for images , respectively, showing that most of the inconsistency is due to difference s in morphological interpretation. Improvements can thus be expected only i f diagnostic criteria or methodology are changed. In contrast, kappa for cl assifying DCIS by growth pattern was very low at 0.23 for sections and bett er at 0.47 for images, reflecting the widely recognised variation in the gr owth pattern of DCIS. Higher kappa statistics were obtained when any mentio n of an individual growth pattern was included in that category, thus allow ing multiple categories per case; but kappa was still higher for images tha n sections. Classifying DCIS by nuclear grade gave kappa values of 0.36 for sections and 0.49 for images, indicating that intralesional heterogeneity has hitherto been underestimated as a cause of inconsistency in classifying DCIS by this method. More rigorous assessment of the proportions of the di fferent nuclear grades present could lead to an improvement in consistency. (C) 2000 Elsevier Science Ltd. All rights reserved.