Yamada Y, Sakamoto S, Rii J, et al. - A retrospective multicenter cohort study was conducted to propose a novel definition for “high-volume” prostate cancer in Asians. Between 1999 and 2017, researchers retrospectively pursued 426 individuals with de novo metastatic castration-naïve prostate cancer from multiple institutions. The number of bone metastases at diagnosis was evaluated to elucidate the clinical significance for progression-free survival and overall survival (OS). By using the Mann-Whitney U test, Cox proportional hazard models, and Kaplan-Meier methods, the statistical analyses were conducted. Individuals with ≥ 11 bone metastases displayed the highest HR for OS (2.766). Compared with ≤ 10 metastases individuals with 11 to 20 bone metastases had a significantly shorter OS. It was demonstrated that the modified criteria were the only independent prognostic factors for OS in multivariate analysis. There were no significant differences in OS between individuals with 1 to 3 bone metastases and 4 to 10. In Asians, the study implied ≥ 11 bone metastases as a suitable definition for “high-volume” prostate cancer. A larger, prospective study is needed to verify the findings.