The New Prostate Cancer Grading System Does Not Improve Prediction of Clinical Recurrence After Radical Prostatectomy: Results of a Large, Two-Center Validation Study

BACKGROUND A new prostate cancer (PCa) grading system (namely, Gleason score-GS- ≤6 vs. 3 + 4 vs. 4 + 3 vs. 8 vs. ≥9) was recently proposed and assessed on biochemical recurrence (BCR) showing improved predictive abilities compared to the commonly used three-tier system (GS ≤6 vs. 7 vs. ≥8). We assessed the predictive ability of the five-tier grade group (GG) system on harder clinical endpoint, namely clinical recurrence (CR). METHODS Between 2005 and 2014, 9,728 clinically localized PCa patients were treated with radical prostatectomy (RP) at two tertiary referral centers. Kaplan–Meier curves, multivariable Cox regression analyses, and concordance index (C-index) were used to assess CR after treatment according to four Gleason grade classifications at biopsy and RP: Group 1: ≤6 versus 7 versus ≥8; Group 2: ≤6 versus 3 + 4 vs. 4 + 3 versus ≥8; Group 3: ≤6 versus 7 versus 8 versus ≥9; Group 4: ≤6 versus 3 + 4 versus 4 + 3 versus 8 versus ≥9. Same analyses were repeated in patients who had BCR (n = 1,624). Decision curve analyses were performed to evaluate and compare the net benefit associated with the use of the four Gleason grade classifications. RESULTS Overall, 443 (4.6%) patients had CR. The hazard ratio of the GS 3 + 4, 4 + 3, 8, and ≥9 relative to GS ≤6 were 3.63, 5.93, 11.44, 18.08 and 4.93, 9.99, 15.31 and 25.12 in the pre- and post-treatment models, respectively. The C-index of the five-tier GG system was slightly higher relative to the other 3 Gleason grade classifications both in the pre- (range: 0.001–0.006) and post-treatment models (range: 0–0.008). Similar findings were observed when we focused our analyses in patients with BCR after RP. The use of the five-tier GG system did not result into higher net-benefit relative to the other three Gleason grade classifications. CONCLUSIONS The difference in accuracy between the five-tier GG system and the other Gleason grade classifications, using CR as an endpoint, is clinically negligible. Current evidence suggests that the five-tier GG system represents a simplified user-friendly scheme available for patient counseling rather than a new histopathological diagnostic system that improves the prediction of CR. Prostate © 2016 Wiley Periodicals, Inc.