Introduction: The aim of this study was to validate contemporary grading systems, in particular, the Gleason grade group (GGG) 5. Patients and Methods: We retrospectively reviewed the clinicopathologic data of 176 patients who underwent radical prostatectomy and whose pathologic results were GGG 4 or 5. The endpoints were biochemical recurrence (BCR) and castration-resistant prostate cancer (CRPC). Results: The GGG 4 group was composed of 69 patients. The GGG 5 group consisted of 78 patients with GS 4+5 and 29 patients with GS 5+4 or higher. The 5-year BCR-free survival rates for men with GGG 4, GS 4+5, and GS 5+4 or higher were 59%, 54%, and 20%, respectively, and the 5-year CRPC-free survival rates were 98%, 100%, and 88%, respectively. Both the BCR- and CRPC-free survival rates were significantly higher in GS 4+5 than in GS 5+4 or higher (P < .001 and P = .002, respectively), but there were no significant differences between GGG 4 and GS 4+5 (P = .702 and P = .803, respectively). The multivariate analysis demonstrated that GS 5+4 or higher (hazard ratio, 3.4; P = .002) and lymphovascular invasion (hazard ratio, 3.4; P < .001) greatly affected BCR. Conclusion: Our follow-up study revealed that men with GS 4+5 and those with GGG 4 had a similar prognosis. However, there was a significant discrepancy in prognosis between GS 4+5 and GS 5+4 or higher. This suggested that GGG 4 and 5 in the contemporary prostate cancer grading system should be reviewed. Furthermore, lymphovascular invasion may be useful to subgroup these pathologically high-risk patients.
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