Histological Grading of Prostatic Carcinoma in Prostatectomy Specimens: Comparison of Prognostic Accuracy of Five Grading Systems

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Abstract
Summary—The prognostic accuracy of 5 histological grading systems (Broders, Anderson, Mostofi, Gleason and Mostofi‐Schroeder) was compared. Grading was performed on 50 prostatectomy specimens by 5 pathologists. The results were averaged so as to reduce the impact of inter‐observer variation. The Cox proportional hazards model was used to estimate the relationship between average grading scores and both time‐to‐recurrence and time‐to‐death by prostatic carcinoma. Age at surgery was considered to be a possible confounding factor and adjusted accordingly. The prognostic impact of the 5 grading systems (related to both recurrence and death caused by prostatic carcinoma) was judged by the likelihood ratio (LR) test score (χ2distributed with 1 df); for time‐to‐recurrence for the Mostofi‐Schroeder score the LR was 6.54 and for the Gleason system it was 1.79. A stepwise procedure demonstrated that the best prognostic performance was reached with the Mostofi‐Schroeder and Broders systems used together (with Mostofi‐Schroeder weighted 1.5 times larger than Broders). For time‐to‐recurrence the median grading result was also used, giving results similar to the mean grading result. For time‐to‐death from prostatic carcinoma the LR test scores for all grading systems were relatively low. In this analysis the outcome of the Gleason system showed a minimum of prognostic ability, whereas the Broders and Mostofi‐Schroeder systems had a reasonable predictive ability. Since the inter‐observer variation of the Mostofi‐Schroeder system was large, the Broders system is preferable. The restrictions and implications of this study are discussed and a brief review of the prognostic importance of grading of prostatic carcinoma is presented.