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

Abstract

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 < 0.05). Furthermore, patients in the beneficial group had a significantly longer OS (P < 0.05). Regarding safety, one and three patients in the beneficial and non-beneficial groups, respectively, prematurely discontinued radium-223 because of an increased prostate-specific antigen level, decreased hemoglobin level, or femoral fracture. Conclusion: Radium-223 appears generally safe in this population. Patients with good bone scan index response have better performance status, receive more injections of radium-223, and achieve OS prolongation. Bone scan index is a useful biomarker of survival outcomes and can be a valuable assessment tool in patients with metastatic castration-resistant prostate cancer who are treated with radium-223.