Initial treatment outcome and feasibility of low-dose cabazitaxel against docetaxel- and castration-resistant prostate cancer in a Japanese hospital.

Cabazitaxel (CBZ) is used worldwide for castration-resistant prostate cancer after docetaxel treatment. In July 2014 the drug was approved in Japan with the same induction dose used for Caucasian patients. In this study, we examined and compared the results of an initial low-dose CBZ treatment in patients admitted to our hospital. Between July 2014 and August 2018, sixteen mCRPC patients were enrolled and underwent a low-dose CBZ treatment at our hospital. We compared the results with those of a Japanese metastatic docetaxel- and castration-resistant prostate cancer Phase I study. The median patient age was 77 years (range, 53-84 years). Of the 16 patients, eight (50%) had a lymph node metastasis and 11 (68.8%) had a distant metastasis, 10 of whom had only a bone metastasis. The median dose of CBZ was 30 mg (range, 20-32 mg) and the median number of CBZ cycles was 2.5 (range, 1-18). The PSA level of 9 (56.3%) patients decreased after CBZ treatment, including 4 (25%) who showed a decrease to <50%. The median time interval in which the PSA level decreased was 2 months (range, 1-18 months). The observed adverse events (AE) were neutropenia (31.3%), febrile neutropenia (6.3%), fatigue (43.8%), nausea (18.8%), diarrhea (12.5%), decreased appetite (25%), dysgeusia (6.3%), white blood cell count decrease (43.8%), platelet count decrease (12.3%), and anemia (75%). However, no patient listed an AE as the reason for discontinuing the treatment. Even at a low dose, CBZ could improve the PSA value in patients with CRPC previously treated with docetaxel. Dose reduction and prophylactic administration of sustained G-CSF were also safe treatment options. Further studies involving an introduction period including a modulation of duration and dose are necessary, especially in Japanese patients.