Treatment outcomes with radium-223 in patients with metastatic castration-resistant prostate cancer with bone metastasis in real-world practice: a multiinstitutional study.

Background: Radium-223 (Ra-223) treatment is used to extend the overall survival (OS) of patients with metastatic castration-resistant prostate cancer (mCRPC) with bone metastases. However, the optimal timing for its administration remains ambiguous. Hence, this study aimed to determine the optimal timing for Ra-223 administration. Materials and methods: We retrospectively included Japanese men with mCRPC with bone metastases who were treated with Ra-223. The primary endpoint was OS from Ra-223 treatment. Secondary endpoints included the maximum reduction in alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and prostate-specific antigen (PSA) levels and the incidence of adverse events following Ra-223 treatment. The exploratory endpoint was the association between clinical parameters and OS. Results: Overall, 100 men with mCRPC with bone metastasis treated with Ra-223 wereenrolled. The median OS from the Ra-223 treatment was 38.6 months. Post Ra-223 treatment, ALP, LDH, and PSA levels decreased in 78.6%, 56.1%, and 44.9% of patients, respectively. Grade ≥3 anemia occurred in three (4.1%) patients. The median OS of patients with ≥10 months from diagnosis to developing mCRPC (52.4 months, P < 0.014), a PSA doubling time ≥3 months (52.4 months, P = 0.035), prior docetaxel (DOC) treatment (108.2 months, P = 0.002), five or less numbers of bone metastasis (97.9 months, P = 0.006), five or more cycles of Ra-223 treatment (46.1 months, P = 0.045), hemoglobin measuring ≥13.1 g/dl (52.4 months, P = 0.003), ALP measuring ≤260 (54.8 months, P = 0.003), or LDH measuring ≤220 (46.1 months, P = 0.002) was significantly longer than that of those who had <10 months from diagnosis to developing mCRPC, a PSA doubling time <3 months, absence of prior DOC treatment, more than five bone metastasis, less than four cycles of Ra-223 treatment, hemoglobin measuring <13.1 g/dl, ALP measuring >260, or LDH measuring >220. Multivariate analysis showed that prior DOC administration prolonged the OS. Conclusions: Ra-223 treatment is safe and effective for mCRPC.