Abstract
BACKGROUND: Management of metastatic prostate cancer often requires combining androgen deprivation therapy (ADT) with novel androgen receptor signaling inhibitors (ARSIs). Although these agents improve survival, older patients may face acute care utilization from medication burden, reflected in polypharmacy and nonadherence. METHODS: Using SEER-Medicare data, the authors identified patients ≥66 years old with de novo metastatic prostate cancer prescribed abiraterone, enzalutamide, or apalutamide (2010-2017). Polypharmacy was defined by the Youden index (≥8 medications). ARSI adherence was measured by medication possession ratio (≥0.8) from initiation to discontinuation, assessed over 6 months. Acute care use was defined as any inpatient hospitalization or emergency visit within 6 months. Demographic characteristics were compared by t-tests/χ(2). Negative binomial regression estimated incidence rate ratios (IRRs) for acute care use. RESULTS: Among 2697 patients (mean age, 75 years), most were White (80.3%), married (63.1%), and received prior ADT (85.3%). Polypharmacy was present in 50.6% of patients before ARSI initiation, whereas ARSI nonadherence in the 6 months post-initiation was 34.0%. Polypharmacy and adherence were not significantly associated. In adjusted analyses controlling for demographic, clinical, and treatment factors, both polypharmacy (IRR, 1.59; 95% confidence interval [CI], 1.28-1.98) and ARSI nonadherence (IRR 2.50; 95% CI, 2.00-3.03) independently prognosticated higher acute care use. CONCLUSIONS: Medication burden, as characterized by suboptimal adherence and polypharmacy, is an independent risk factor for acute care use among older adults initiating ARSI treatment for metastatic prostate cancer. These findings highlight an opportunity for potential interventions to reduce downstream acute care use.