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.