Prostate-specific antigen doubling time following radium-223 treatment as a predictor of the clinical course in patients with metastatic castration-resistant prostate cancer

OBJECTIVES: To identify useful biomarkers by reviewing laboratory data for a predictor of the clinical course following treatment with radium-223 dichloride (Ra-223) in patients with metastatic castration-resistant prostate cancer. METHODS: Eighteen metastatic castration-resistant prostate cancer patients who were administered Ra-223 at our hospital were retrospectively enrolled in this study. Prostate-specific antigen doubling times before and after the administration of Ra-223 were evaluated as prognostic factors for metastatic castration-resistant prostate cancer patients treated with Ra-223 using the Kaplan–Meier method and Log-rank test. RESULTS: Four patients failed to complete the planned six-time Ra-223 treatments with the exacerbation of their condition. In the 14 patients who completed the planned Ra-223 treatment, before the Ra-223 treatment, no significant differences were observed in overall survival between patients with prostate-specific antigen doubling time of 6 months or less and those with prostate-specific antigen doubling time of more than 6 months or stable (p = 0.642). Following the completion of the Ra-223 treatment, overall survival was significantly shorter in patients with prostate-specific antigen doubling time of 6 months or less than in those with prostate-specific antigen doubling time of more than 6 months or stable (p = 0.007). CONCLUSION: Prostate-specific antigen doubling time after the Ra-223 treatment is a useful predictor of the clinical course following treatment in metastatic castration-resistant prostate cancer patients.