Alternative prostate cancer grading systems incorporating percent pattern 4/5 (IQ-Gleason) and cribriform architecture (cGrade) improve prediction of outcome after radical prostatectomy

Percentage Gleason pattern 4, invasive cribriform and/or intraductal carcinoma (IC/IDC) and minor pattern 5 are recognized as independent parameters for prostate cancer outcome, but are not incorporated in current grade groups (GGs). Two proof-of-principle studies have proposed alternative grading schemes based on percentage Gleason pattern 4/5 (integrated quantitative Gleason score; IQ-Gleason) and IC/IDC presence (cribriform grade; cGrade). Our objective was to compare the performance of GG, IQ-Gleason and cGrade for predicting biochemical recurrence and metastasis after radical prostatectomy (RP). RP specimens of 1064 patients were pathologically reviewed and graded according to the three schemes. Discriminative power for prediction of biochemical recurrence-free (BCRFS) and metastasis-free (MFS) survival was compared using Harrell’s c-index. The GG distribution at RP was 207 (19.4%) GG1, 472 (44.4%) GG2, 126 (11.8%) GG3, 140 (13.2%) GG4 and 119 (11.2%) GG5. Grading according to 5-tier IQ-Gleason and cGrade systems led to categorical shifts in 49.8% and 29.7% of cases, respectively. Continuous IQ-Gleason had the best performance for predicting BCRFS (c-index 0.743, 95% confidence interval (CI) 0.715–0.771), followed by cGrade (c-index 0.738, 95%CI 0.712–0.759), 5-tier categorical IQ-Gleason (c-index 0.723, 95%CI 0.695–0.750) and GG (c-index 0.718, 95%CI 0.691–0.744). Continuous IQ-Gleason (c-index 0.834, 95%CI 0.802–0.863) and cGrade (c-index 0.834, 95%CI 0.808–0.866) both had better predictive value for MFS than categorical IQ-Gleason (c-index 0.823, 95%CI 0.788–0.857) and GG (c-index 0.806, 95%CI 0.777–0.839). In conclusion, the performance of prostate cancer grading can be improved by alternative grading schemes incorporating percent Gleason pattern 4/5 and IC/IDC.