The importance of primary Gleason grade among men with Gleason score 7 disease has been well-defined. However, this dichotomization may oversimplify the continuous spectrum of absolute percent Gleason grade 4 disease (G4%). In this study we report the prognostic value of G4% in cancer related outcomes of men undergoing radical prostatectomy.

Patients who underwent radical prostatectomy for clinically localized Gleason 6-8 prostate cancer from 2005 to 2013 were included in the study. G4% was determined as biopsy tumor length containing Gleason pattern 4/total tumor length, which performed better than alternative quantifications of pattern 4 involvement. G4% was correlated with time to biochemical recurrence and presence of adverse radical prostatectomy pathology, defined as primary Gleason 4 or pT3 or greater, by multivariable Cox and logistic regressions.

Of 1,691 patients 517 (30.6%) had adverse pathological features and 86 (5.6%) experienced biochemical recurrence. On multivariable analyses G4% was a significant predictor of adverse pathology (OR 1.04, 95% CI 1.03-1.05) and time to biochemical recurrence (HR 1.02, CI 1.01-1.03). G4% was also a significant independent predictor of adverse pathology in subsets of patients with Gleason score 7 (OR 1.05, 95% CI 1.03-1.06), 3+4 (OR 1.06, 95% CI 1.04-1.08) and 4+3 cancer (OR 1.05, 95% CI 1.03-1.06). We found a significantly increased risk of adverse pathology at potentially meaningful G4% thresholds (1% to 10% vs 20% to 30%).

The incremental percentage of Gleason grade 4 disease in biopsy specimens is an important predictor of adverse pathology and biochemical recurrence across the entire range of G4% disease. Accounting for G4% can improve risk assessment even among those patients with Gleason 3+4 or 4+3 cancer and may help inform patient counseling.