Objectives: Abiraterone acetate (ABI) and enzalutamide (ENZ) are the first two oral novel hormonal therapies (NHTs) approved for treatment of metastatic castration-resistant prostate cancer (mCRPC). The objectives were to compare prostate cancer (PCa)-related and all-cause emergency department (ED) utilization between ABI and ENZ and examine the impact of demographic and clinical characteristics on ED utilization.

Methods: This study utilized 2013-2017 Humana Medicare medical and prescription claims data and included continuously enrolled (6 months pre- to 12 months post-index) men aged>65 with PCa as the primary cancer, with one inpatient/outpatient PCa diagnosis, and at least one prescription for ABI or ENZ. The index date was the first NHT prescription date. Dependent variables included proportion of men with ≥1 PCa-related and all-cause ED visits. Index NHT type was the primary predictor variable and demographic and clinical characteristics served as covariates. Statistical methods included chi-square tests and multiple logistic regression (MLR).

Results: Among included patients (N=1,254), unadjusted analyses showed no significant differences in PCa-related (23.3% vs. 18.9%) or all-cause (53.5% vs. 49.4%) ED visits between ABI and ENZ. The adjusted MLR model for PCa-related ED visits indicated significantly (p<0.05) lower odds of ≥1 PCa-related ED visits in: 66-70 age group (vs. ≥85), men with lymph node metastases only and other metastases (vs. >1 metastasis), and adherent men (vs. non-adherent). Regarding ≥1 all-cause ED visits, MLR model indicated (p<0.05): lower odds in 66-70, 71-74, and 75-80 age groups (vs. ≥85), men with other metastases (vs. >1 metastasis), and adherent (vs. non-adherent); while higher odds in men with Klabunde Comorbidity Index (NCICI)≥2 (vs. NCICI=0), after controlling for covariates.

Conclusion: While ED utilization was similar between ABI and ENZ, older age groups, greater number of metastases, and non-adherence to NHTs were significantly associated with higher ED utilization. Additional efforts are needed to improve adherence to NHTs.