Second line cabazitaxel treatment in castration-resistant prostate cancer (CRPC) clinical trials compared to standard of care in CAPRI: an observational study in the Netherlands

Abstract Aim Cabazitaxel has been shown to improve overall survival (OS) in mCRPC patients after docetaxel in the TROPIC trial. However trial populations may not reflect the real world population. The objective is to compare patient characteristics and outcome of cabazitaxel within and outside trials (standard of care - SOC). Methods mCRPC patients treated with cabazitaxel directly after docetaxel before 2017 were retrospectively identified and followed to 2018. Patients were grouped based on treatment within a trial or SOC. Outcomes included OS and PSA response. Results From 3,616 patients in the CAPRI registry, we identified 356 patients treated with cabazitaxel, of whom 173 patients in second line. Trial patients had favorable prognostic factors: less symptoms and visceral disease, lower LDH, higher hemoglobin, more docetaxel cycles and a longer treatment-free interval since docetaxel. PSA response (≥ 50% decline) was 28 vs 12%, respectively (p=0.209). mOS was 13.6 vs 9.6 months for trial and SOC subgroups, respectively (HR 0.73, p=0.067). After correction for prognostic factors, there was no difference in survival (HR 1.00, p=0.999). Longer duration of ADT treatment, lower LDH and lower PSA were associated with longer OS; visceral disease had a trend for shorter OS. Conclusion Patients treated with cabazitaxel in trials were fitter and showed outcomes comparable to registration trials. Conversely those treated in daily practice showed features of more aggressive disease and worse outcome. This underlines the importance of an adequate estimation of the trial eligibility and health status of mCRPC patients in daily practice to ensure optimal outcomes.