Association of Cabazitaxel Treatment Beyond 10 Cycles with Survival Outcomes in Metastatic Castration-Resistant...

Background/Objectives: Cabazitaxel is an established treatment option for patients with metastatic castration-resistant prostate cancer (mCRPC), but outcomes beyond the conventional 10-cycle threshold remain incompletely characterized. This threshold largely reflects clinical trial design. We therefore evaluated outcomes associated with cabazitaxel treatment beyond 10 cycles using a predefined 8-month landmark analysis intended to reduce early immortal time bias. Methods: This retrospective single-center study included 98 patients with mCRPC treated with cabazitaxel between 2010 and 2020. The final cohort comprised 74 patients who were alive at the predefined 8-month landmark. The primary endpoint was overall survival (OS) from the landmark, and secondary endpoints included conditional radiologic progression-free survival (rPFS), conditional prostate-specific antigen progression-free survival (PSA-PFS), treatment response, and safety. Results: Among the 74 patients included in the landmark cohort, 45 (60.8%) ultimately received ≤10 cycles and 29 (39.2%) received >10 cycles. The median landmark OS was numerically longer in the >10-cycle group (17.6 vs. 10.4 months; p = 0.123). Conditional rPFS and PSA-PFS did not differ significantly between groups (>10 vs. ≤10 cycles: 4.4 vs. 2.3 months; p = 0.255 and 4.2 vs. 2.2 months; p = 0.137, respectively). In a broader baseline-adjusted sensitivity model, the treatment duration association was not statistically significant (HR for ≤10 vs. >10 cycles, 1.58; 95% CI, 0.91-2.74; p = 0.105). The crude cumulative proportions of grade ≥3 neutropenia and febrile neutropenia were higher in the >10-cycle group. Conclusions: Cabazitaxel treatment beyond 10 cycles appeared feasible in selected patients. However, future-derived exposure classification and responder enrichment limit causal interpretation. The survival association was not consistently maintained across sensitivity analyses, supporting a hypothesis-generating interpretation rather than evidence of a survival benefit from continuation beyond 10 cycles.