OBJECTIVES: Novel hormonal agents such abiraterone (ABI) and enzalutamide (ENZA) have both demonstrated survival benefits in the post-chemotherapy setting in metastatic castration-resistant prostate cancer (mCRPC). However, there are currently no randomized head-to-head comparisons of both agents. The objective was to compare the effectiveness of ABI and ENZA as second-line treatments in the post-chemotherapy setting in patients with mCRPC.

METHODS: A retrospective population-based cohort was extracted from Quebec public healthcare administrative databases. Patients were selected on the basis of having sequentially received androgen deprivation therapy and chemotherapy prior to initiating a novel hormonal agent (ABI or ENZA) between 2012 and 2016. The index date corresponded to the date of the first prescription of ABI or ENZA. Kaplan Meier analysis and multivariable Cox proportional hazards regression were used to evaluate the primary outcome of overall survival.

RESULTS: The cohort is comprised of 621 patients, with 542 in the ABI group and 79 in the ENZA group. Median overall survival was 15.4 months in the ABI group and 17.9 months in the ENZA group (log-rank p=0.822). On multivariable analysis, the hazard ratio (HR) for ABI versus ENZA was 0.98 (95%CI 0.69-1.40; p=0.884). Age greater than 75 (HR 1.40; 95%CI 1.16-1.69; p=0.001), Charlson comorbidity scores greater than 2 (HR 1.35; 95%CI 1.09-1.66; p=0.005), presence of symptoms (HR 1.66; 95%CI 1.37-2.00; p<0.001), time from prostate cancer diagnosis < 3 years (HR 1.61; 95%CI 1.27-2.03; p<0.001), and time from last chemotherapy < 6 months (HR 1.24; 95%CI 1.01-1.54; p=0.038) were associated with worse survival.

CONCLUSIONS: In our study population, there was no difference in overall survival between ABI and ENZA as second-line treatments in the post-chemotherapy setting in mCRPC. Further evaluation of both drugs using real-world data are necessary to assess differences in other health outcomes such treatment-related complications and use of health services.