Significant prognostic difference between Grade Group 4 and 5 in the 2014 International Society of Urological Pathology Grading System for High Grade Prostate Cancer with Bone Metastasis

Background To investigate prognostic difference between Gleason Score (GS) 8 and 9-10, as the 2014 International Society of Urological Pathology Gleason Grading Systems proposed, in patients with prostate cancer (PCa) with bone metastasis. Materials and methods We retrospectively reviewed data on 106 patients with GS 8-10 between 2006 and 2016. All patients received androgen deprivation therapy immediately. We validated biochemical recurrence, PCa-specific survival, and overall survival, and analyzed the predictive value for overall survival. Results Patients with GS 9-10 had significantly lower PCa-specific survival (50.5% vs. 83.4%, P = 0.01) and overall survival (38.8% vs. 66.3%, P = 0.04) at 5 years than those with GS 8, while biochemical recurrence rate was not significantly different (P = 0.26). Furthermore, these significant differences between GS 8 and 9-10 were also observed among high-risk groups proposed in Japan Cancer of the Prostate Risk Assessment Stratification (prostate cancer-specific survival: P = 0.03, overall survival: P = 0.04, respectively). Pathological GS 9-10 was an independent prognostic factor for overall survival (hazard ratio = 1.97, P = 0.04) in multivariable cox proportional hazard regression analysis. Among patients with GS 9-10, albumin level was an only prognostic factor for overall survival (hazard ratio = 0.33, P < 0.01). Conclusion Pathological GS 9-10 predicts significantly worse outcomes than GS 8 in Japanese PCa patients with bone metastasis. Our data indicated clinical significance of discriminating the 2014 International Society of Urological Pathology Gleason Grading Group 4 and 5 among high-risk PCa patients with bone metastasis.