Behavior of total alkaline phosphatase after radium-233 therapy in metastatic castration-resistant prostate cancer: a single-center, real-world retrospective study

OBJECTIVE: To describe the behavior of total alkaline phosphatase (tALP) in patients with metastatic castration-resistant prostate cancer receiving radium-223 therapy, in a real-world scenario, and to describe overall survival (OS) among such patients. MATERIALS AND METHODS: This was a retrospective study involving 97 patients treated between February 2017 and September 2020. Patients were stratified by the baseline tALP (normal/elevated). A tALP response was defined as a ≥ 30% reduction from baseline at week 12. For patients with elevated baseline tALP, we also evaluated treatment response as a ≥ 10% reduction in tALP after the first cycle of treatment. We defined OS as the time from the first treatment cycle to the date of death. RESULTS: There was a significant reduction in the median tALP after each cycle of treatment (p < 0.05 for all). Data for tALP at week 12 were available for 71 of the 97 patients. Of those 71 patients, 26 (36.6%) responded. Elevated baseline tALP was observed in 47 patients, of whom 19 (40.4%) showed a response. Longer OS was observed in the patients with normal baseline tALP, in those with elevated baseline tALP that showed a response to treatment (≥ 10% reduction), and in those who received 5-6 cycles of therapy. CONCLUSION: The tALP may be used to predict which patients will benefit from treatment with a greater number of cycles of radium-223 therapy and will have longer OS.