HISTOLOGICAL GRADING OF BREAST CARCINOMAS - A STUDY OF INTEROBSERVER AGREEMENT

Interobserver variation in the histological grading of breast carcinom a was investigated using the hypothesis that optimal fixation, more pr ecise grading guidelines, some experience, the use of training and tes t sets, and a comparison of results with an expert group might allow h igher levels of agreement. For the training sets sections from 50 cons ecutive cases of breast carcinoma received at the Sir Charles Gairdner Hospital (SCGH) and fixed in both B5 and buffered formal saline (BFS) were graded by consensus of three pathologists at the SCGH and indepe ndently by consensus of two pathologists at the Nottingham City Hospit al (NCH) using a modified Scarff-Bloom-Richardson histological grading system with guidelines as suggested by NCH pathologists. The section quality and degree of preservation of nuclear morphology were judged b y NCH pathologists to be superior for B5-fixed material. Complete agre ement in grade between SCGH and NCH results was achieved for 83.3% of B5-fixed cases and 73.5% of BFS-fixed cases (P =.05) with relative dis agreement rates (RDRs) of 0.15 and 0.29 and kappa statistic values of 0.73 and 0.58, respectively. Approximately 80% complete agreement was achieved for tubule formation, nuclear score, and mitotic count, with RDRs ranging from 0.19 to 0.27 and kappa values from 0.46 to 0.69. The re was a consistent bias in the SCGH results toward a higher tubule sc ore in both B5 and BFS-fixed material because of a difference in inter pretation of cribriform or complex gland patterns and a consistent bia s in SCGH results toward a lower nuclear size/pleomorphism score for B 5 and BFS material. For the test set sections from 50 further consecut ive cases of breast cancer fixed in B5 were examined using similar cri teria but taking into account the sources of error shown by the traini ng set. Approximately 80% complete agreement was again achieved for gr ade components and grade (RDRs, 0.18 and 0.72). Systematic bias was re duced in the test set, but no other improvement was observed. Of the t umors designated as grade I by NCH, 87.5% were called grade I tumors b y SCGH in the B5 training set, 84.6% in the B5 test set, and 66.6% in the BFS training set. The levels of agreement shown in both the traini ng and test sets were satisfactory and represented a significant impro vement over our previous study, suggesting that experience and precise grading guidelines are of value. The similar levels of agreement in t raining and test sets suggest that reasonable results can be achieved without direct training by expert groups. The value of optimal fixatio n may be the most important variable noted by the study. Copyright (C) 1995 by W.B. Saunders Company.