INTEROBSERVER REPRODUCIBILITY OF THE NOTTINGHAM MODIFICATION OF THE BLOOM AND RICHARDSON HISTOLOGIC GRADING SCHEME FOR INFILTRATING DUCTAL CARCINOMA

The interobserver reproducibility of the Nottingham modification of th e Bloom and Richardson histologic grading scheme for invasive breast c arcinoma was tested. Six surgical pathologists from four institutions independently evaluated histologic grade and each of its three compone nts for 75 infiltrating ductal carcinomas. The number of slides per ca se ranged from one to nine (median 3). Pairwise kappa values for agree ment ranged from moderate to substantial (0.43-0.74) for histologic gr ade. Generalized kappa values indicated substantial agreement for tubu le formation (0.64), moderate agreement for mitotic count (0.52), and near moderate agreement for nuclear pleomorphism (0.40). Normalizing t he mitotic counts per mm(2) showed only slight improvement in agreemen t over the published range of mitotic counts for three different field areas. The results suggest that steps to discriminate between categor ies for nuclear pleomorphism would likely be of benefit for improving the interobserver reproducibility of histologic grade. Nevertheless, t he Nottingham modification of the Bloom and Richardson grading system is recommended as a suitable scheme for evaluating invasive breast car cinomas in the routine clinical setting.