Bone scan index can be a useful biomarker of survival outcomes in patients with metastatic castration‐resistant prostate cancer treated with radium‐223

Background Bone metastasis of prostate cancer is associated with pain and reduced overall survival (OS). Radium‐223, which is expected to reduce bone pain and prolong OS, was recently approved in Japan. Aim The aim of this study was to investigate the usefulness of the bone scan index by comparing the outcomes and factors according to response in Japanese patients treated with radium‐223. Methods and results Twenty patients receiving radium‐223 were divided into two groups according to whether they did or did not achieve a bone scan index decrease of at least one point (beneficial and non‐beneficial groups, respectively). The clinical characteristics at baseline and after three and six treatment cycles were compared using χ2 tests and Student's t‐tests or Mann–Whitney U tests, and survival was estimated and compared using the Kaplan–Meier method and log‐rank test, respectively. Fourteen (70%) and six patients (30%) were categorized into the beneficial and non‐beneficial groups, respectively. Patients in the former group were significantly more likely to have a higher Eastern Cooperative Oncology Group performance status score and receive a greater number of radium‐223 injections (P