Comparison of biopsy gleason pattern 4 percentage and length in grade group 2 prostate cancer patients

Quantification of biopsy Gleason pattern (GP) 4 contributes to risk assessment and supports clinical decision-making in Grade Group 2 (GG2) prostate cancer (PCa) patients. The optimal methodology for assessment of GP4 quantity is yet unclear. The objective of this study is to compare the mutual relation and performance of biopsy GP4 quantification methods to predict biochemical recurrence-free survival (BCRFS) after radical prostatectomy (RP). Ninety-four patients with biopsy GG2 PCa who underwent RP were included. We recorded overall GP4 percentage and cumulative GP4 length (mm) across all cores, as well as the maximum percentage and length within a single core. Quantification methods were compared using Spearman's rank correlation and Cox proportional hazard regression for BCRFS. All biopsy GP4 quantification methods were mutually correlated (rho coefficients varying from 0.655 to 0.935; P < 0.001), while correlation with GP4 percentage at RP was weak to moderate (rho coefficient range 0.260 to 0.326; P < 0.02). All biopsy GP4 quantification methods significantly predicted post-operative BCRFS. Absolute GP4 measures had better discriminative performance than percentages (cumulative GP4 length Hazard Ratio [HR] 1.14; 95% Confidence Interval [95% CI] 1.07-1.22; P < 0.001; c-index 0.711; overall GP4 percentage HR 1.05; 95% 1.01-1.09; P = 0.007; c-index 0.635). Adding GP3 percentage or length did not have added value (P > 0.5) for predicting BCRFS once absolute GP4 length was known. Absolute GP4 length (mm) in biopsy GG2 PCa patients has better predictive value for post-operative BCRFS than GP4 percentage. GP3 volume does not add to prediction once GP4 volume is known.