Histological evaluation of prostatic cancer. (II): Reproducibility of a histological grading system

The aim of this study was to evaluate the reproducibility, expressed by kappa coefficients, of the histological grading system of prostatic cancer as proposed by Schroeder, Hop, Blom and Mostofi in 1985. This grading system has five prognostic groups based on combinations of growth pattern, mitoses and nuclear anaplasia. All histological slides from 85 cases of prostatic carcinoma were blindly evaluated on two independent occasions by each of four pathologists. The overall INTER-observer agreement and mean INTRA-observer agreement regarding "prognostic group" were 0.55 and 0.69 respectively, whereas the kappa coefficients were 0.38 and 0.57 respectively. An acceptable level of INTER-observer reproducibility of prognostic group I (kappa = 0.70), of the parameter "growth pattern" (kappa = 0.60) and of "slight nuclear anaplasia" (kappa = 0.62) was found. A low overall kappa coefficient of "mitoses" and "nuclear anaplasia" was found. Based on the well reproducible parameters a simplified grading system is proposed.