Neutropenia in Patients With Castration-Resistant Prostate Cancer Treated Using Cabazitaxel and Prophylactic Administration of Pegfilgrastim.

Background and Aims: Cabazitaxel has demonstrated survival benefits in patients with metastatic castration-resistant prostate cancer (CRPC). However, Japanese patients are reported to experience higher rates of hematologic toxicity compared to their Caucasian counterparts. Although primary prophylaxis with pegfilgrastim is now routinely used in clinical practice, febrile neutropenia (FN) may still occur. In this study, we aimed to evaluate the real-world safety of cabazitaxel with universal pegfilgrastim prophylaxis in Japanese patients with CRPC, particularly focusing on FN during the first treatment cycle. Methods: We retrospectively evaluated 86 patients with CRPC who received cabazitaxel at Showa Medical University-affiliated hospitals between 2015 and 2021. Cabazitaxel was administered every 3-4 weeks at doses determined by the treating physicians, generally 20-25 mg/m Results: Among the 86 patients, FN occurred in 12 patients (14.0%) during the entire treatment course, including 8 events (9.3%) during the first cycle. In univariate analyses, the only factor significantly associated with first-cycle FN was a longer interval from CRPC diagnosis to cabazitaxel initiation (median, 1194.5 vs. 689 days, Conclusion: Despite universal pegfilgrastim prophylaxis, approximately 10% of Japanese patients developed FN during the first cycle of cabazitaxel therapy. A longer interval from CRPC diagnosis to cabazitaxel initiation showed a consistent trend toward association with FN risk in Japanese patients across analyses. These findings provide real-world safety data and highlight the importance of careful hematologic monitoring, particularly in patients treated later in the CRPC disease course.