Evaluation of the Initial Dose and Therapeutic Effect of Cabazitaxel in Japanese Patients

Cabazitaxel (CBZ), used for castration-resistant prostate cancer, has a high frequency of severe myelosuppression. Pegfilgrastim is administered to prevent febrile neutropenia (FN);however, it may still occur, and in many cases, the CBZ dose is reduced for safety considerations. Therefore, a retrospective survey was conducted to investigate the impact of the initial CBZ dose of 25 mg/m 2 on the myelosuppression status, relative dose intensity (RDI), prostate-specific antigen (PSA) response rate, treatment duration , and overall survival (OS) in Japanese patients. In the 25 mg/m 2 group, 6 patients had neutropenia higher than grade 3 (100 ％ ) and 1 patient had FN. There were 26 patients in the reduced-dose group, and neutropenia of ≥ grade 3 was observed in 5 patients (19 ％ ). The frequency of neutropenia was significantly higher in patients aged ≥ 74 years ( P = 0.017). The 25 mg/m 2 group had significantly higher RDI (median: 96 ％ vs 67 ％ , P = 0.016) and PSA response rate (50 ％ vs 19 ％ , P = 0.043) than the reduced-dose group. In contrast, there was no difference between the two groups in terms of treatment duration (median: 5.9 vs 3.3 months, P = 0.220) and OS (median: 10 vs 13.5 months, P = 0.552). The risk of developing ≥ grade 3 neutropenia was low, and no impact on the OS was observed in the reduced-dose CBZ group. It is recommended to reduce the initial dose of CBZ from 25 mg/m 2 to 20 mg/m 2 in Japanese patients.