The efficacy and toxicity of cabazitaxel for treatment of docetaxel-resistant prostate cancer correlating with the initial doses in Japanese patients

Background: We analyzed the efficacy and toxicity of cabazitaxel (CBZ) at high and low initial doses in Japanese patients with docetaxel-resistant castration-resistant prostate cancer (CRPC). Methods: We retrospectively evaluated 118 patients who received CBZ for docetaxel-resistant CRPC in 10 university hospitals in Japan between 2014 and 2016. The rate of decrease of prostate-specific antigen (PSA), adverse events, progression-free survival (PFS), and overall survival (OS) were compared between patients receiving initially high (≥22.5 mg/m², n = 36) and low (≤20 mg/m², n = 80) CBZ doses. Factors associated with survival and grade 4 neutropenia were evaluated. Results: PSA values decreased by > 50% in 22 patients (19%), with a higher frequency in the high-dose group than in the low-dose group (29 and 14%, P = 0.073). The median PFS time for the all-patient, high- and low-dose groups was 2.8 months (95% confidence interval [CI] 1.9-4.4), 2.1 months (1.2-5.5), and 3.0 months (2.0-4.4), respectively (P = 0.904). The median OS times were 16.3 months (95% CI 9.7-30.9), 30.9 months (11.8-47.4), and 10.2 months (8.6-20), respectively (P = 0.020). In multivariate analyses, PFS was significantly associated with existing bone metastasis at diagnosis (P = 0.005) and OS with PSA > 100 ng/ml (P = 0.007), hemoglobin < 12 g/dl (P = 0.030), and low initial CBZ dose (P = 0.030). Grade 4 neutropenia occurred in 53 patients (45%) and was associated with a low CBZ dose (hazard ratio 0.21, 95% CI 0.08-0.59, P = 0.002). Conclusions: CBZ at a higher initial dose may have similar response rate and response duration, but longer survival duration after treatment with higher toxicity than a lower initial dose for docetaxel-resistant CRPC in Japanese patients.