Real-world safety and effectiveness of radium-223 in Japanese patients with castration-resistant prostate cancer (CRPC) and bone metastasis: exploratory analysis, based on the results of post-marketing surveillance, according to prior chemotherapy status and in patients without concomitant use of second-generation androgen-receptor axis-targeted agents

Background: Based on results from Japanese post-marketing surveillance, exploratory analyses were performed to investigate real-world outcomes of radium-223 for metastatic CRPC (mCRPC) according to patient characteristics.

Methods: This non-interventional, prospective study enrolled mCRPC patients selected for radium-223 treatment in clinical practice. Six-month safety and effectiveness were evaluated in subgroups who had/had not received prior chemotherapy (prior-chemo/no prior-chemo groups), and a subgroup who had not received concomitant androgen-receptor axis-targeted agents (ARATs).

Results: In the overall population (n = 296), the prior-chemo group (n = 126) tended to have more bone metastases, more analgesic use, and higher prostate-specific antigen values than the no prior-chemo group (n = 170). Incidences of treatment-emergent adverse events (TEAEs), drug-related TEAEs, and ≥ grade 3 drug-related hematological TEAEs were 47% vs. 53%, 25% vs. 29%, and 4% vs. 7% in the no prior-chemo and prior-chemo groups, respectively. Incidences of TEAEs (61%), drug-related TEAEs (36%), and ≥ grade 3 drug-related hematological events (12%) were numerically higher in 33 patients who had received two lines of prior chemotherapy. Multivariate analysis showed that two lines of prior chemotherapy, and hemoglobin, platelet, and lactate dehydrogenase values were baseline factors significantly related to ≥ grade 2 platelet count decreased. Safety and effectiveness in patients without concomitant ARATs (n = 201) were similar to those in the overall population.

Conclusion: In a real-life setting, radium-223 was well tolerated irrespective of prior chemotherapy, but relatively higher incidences of TEAEs and hematotoxicities were suggested in patients with two lines of prior chemotherapy, possibly reflecting more advanced disease. Radium-223 safety and effectiveness in patients without concomitant ARATs were favorable.