Abiraterone Followed by Enzalutamide Versus Enzalutamide Followed by Abiraterone in Chemotherapy-naive Patients With Metastatic Castration-resistant Prostate Cancer.

BACKGROUND: Abiraterone (AA) and enzalutamide (ENZA) are increasingly being used in chemotherapy-naive patients with metastatic castration-resistant prostate cancer owing to efficacy and favorable toxicity. However, the order in which they should be administered has not been determined. PATIENTS AND METHODS: We retrospectively reviewed the records of chemotherapy-naive patients with metastatic castration-resistant prostate cancer who had received sequential treatment with either AA followed by ENZA (AA-ENZA) or the converse (ENZA-AA). Prostate-specific antigen (PSA) response rates (defined as ≥ 50% PSA decline from baseline), first-line progression-free survival (PFS), second-line PFS, combined PFS (defined as first-line PFS plus second-line PFS), and overall survival are compared between the 2 sequence groups. RESULTS: A total of 97 patients received sequential treatment with AA and ENZA; 50 patients were in the AA-ENZA group, and 47 patients were in the ENZA-AA group. The PSA response rate to first-line treatment was not significantly different between AA (48%) and ENZA (51%) (P = .840). However, a significant difference was observed in the PSA response rate to second-line treatment (AA, 6.4% vs. ENZA, 30%; P = .004). The median combined PFS was not significantly different between sequence groups (hazard ratio, 0.71; 95% confidence interval, 0.46-1.08; log-rank P = .105). The order of addition also had no significant effect on median overall survival (hazard ratio, 0.98; 95% confidence interval, 0.64-1.52; log-rank P = .834). CONCLUSION: With the exception of the second-line PSA response, there was no significant difference in clinical outcomes between the AA-ENZA and ENZA-AA groups. Our results might be useful reference in daily practice, especially for patients who do not have a suitable general condition for chemotherapy.