Sequential Use of Androgen Receptor Axis-targeted Agents in Chemotherapy-naive Castration-resistant Prostate Cancer: A Multicenter Retrospective Analysis With 3-Year Follow-up

Background There has been no established clinical evidence for using sequential treatment in castration-resistant prostate cancer (CRPC). Despite evident cross-resistance, androgen receptor axis-targeted agents (ARTAs), namely abiraterone (ABI) and enzalutamide (ENZ), are often used sequentially owing to less toxicity compared with chemotherapy. Patients and Methods A multicenter retrospective review of chemotherapy-naive patients with CRPC who had received ABI followed by ENZ (ABI-to-ENZ) or ENZ followed by ABI (ENZ-to-ABI) was conducted. Combined progression-free survival (PFS), overall survival (OS), and prostate-specific antigen (PSA) response (≥ 50% PSA decline) to each drug were compared between the 2 groups at the median follow-up of 36.0 months. Results There were no significant differences in combined PFS (12.4 vs. 10.9 months; hazard ratio [HR], 0.94; 95% confidence interval [CI], 0.72-1.23; P = .6594) or OS (28.3 vs 29.3 months; HR, 0.96; 95% CI, 0.66-1.38; P = .8314) between the ABI-to-ENZ and ENZ-to-ABI groups. PSA response rate was not significantly different in first-line ARTAs (48.9% vs. 58.4%; P = .153) but significantly higher in ENZ as a second-line ARTA (40.4% vs. 13.7%; P < .0001). Although multivariate analysis revealed that the ABI-to-ENZ sequence was associated with favorable PFS on second-line ARTA (HR, 0.65; 95% CI, 0.49-0.85; P = .0019), it was not associated with an increased combined PFS or OS. Conclusion With relatively longer follow-up, ARTA sequence did not affect clinical outcomes of CRPC treatment except for PSA response and PFS on a second-line ARTA. These findings will be useful information in clinical decision-making, particularly in chemotherapy-unfit patients with CRPC.