Adherence to abiraterone or enzalutamide in elderly metastatic castration-resistant prostate cancer

Purpose: To evaluate adherence to abiraterone or enzalutamide for the treatment of metastatic castration-resistant prostate cancer (mCRPC). Methods: In an observational prospective cohort study, we monitored patients with mCRPC for their adherence to abiraterone or enzalutamide in the pre- or post-chemotherapy setting. Results: Fifty-eight patients with median age of 76 years (range 56–94), age-adjusted Charlson comorbidity score of 10 (range, 4–15), and geriatric G8 score of 14 (range, 6–17) were enrolled. Twenty-two (38%) patients were treated with abiraterone and 36 (62%) with enzalutamide, while forty-two (72%) were in the pre-chemotherapy setting. Forty-seven patients (81%) had a caregiver. Based on the pill counting, a non-adherence rate of 4.8% and 6.2% was observed for the whole period and the first 3 months, respectively, without a statistically significant difference between abiraterone and enzalutamide cohorts. A lower non-adherence rate (1.3%) was reported by patients during the whole period, mainly due to a misperception (77%) and forgetfulness (19%). Non-adherence rate to the fulfilling of the clinical diary was 38% for the whole period. Non-adherence in the whole period was related to the radiological response (p = 0.03) and geriatric G8 score (p = 0.005). By the receiver operating characteristic (ROC) curve based on the radiological response, non-adherence cut-off was 1.87% (p = 0.04). By this non-adherence cut-off, the G8 cut-off was 14.75 (p = 0.0003). Conclusion: Non-adherence to abiraterone or enzalutamide for mCRPC may have an impact on disease response and be related to patients’ frailty, suggesting their geriatric assessment and clinical interventions to monitor and increase their adherence.