Hospitalizations Among Veterans Treated for Metastatic Prostate Cancer With Abiraterone or Enzalutamide

Abstract

BackgroundAbiraterone and enzalutamide are second generation androgen receptor pathway inhibitors (ARPIs) used to treat advanced or metastatic prostate cancer. Without head-to-head comparative studies identifying 1 agent as preferred initial therapy, physician preferences guide initial ARPI choice. This study compares hospitalizations among patients treated initially with abiraterone versus enzalutamide. Patients and MethodsUnited States veterans treated with abiraterone or enzalutamide between May 13, 2011 and December 31, 2019; then compared hospitalization rate during first treatment with ARPI in the Veterans Healthcare Administration. Baseline incidence rate of hospitalization was determined from data 1 year prior to ARPI. Incidence Rate Difference (IRD) was calculated using χ2 test and difference in IRD using Poisson Regression. Results19,775 veterans were identified; 13,527 (68.4%) were initially treated with abiraterone and 6248 (31.6%) initially with enzalutamide. The enzalutamide cohort was older (75.8 vs. 74.5 years, P < .001) and had higher baseline comorbidities at ARPI initiation (4.4 vs. 4.0, P < .001). Patients were treated with enzalutamide longer than abiraterone (median 9.0 vs. 8.0 months, P < .001). Total hospitalizations increased from 465 per 1000 person-years in the year prior to treatment with abiraterone to 567 during treatment. Total hospitalizations increased from 417 per 1000 person-years in the year prior to treatment with enzalutamide to 430 during treatment. Total rate of hospitalization increased 22% for abiraterone compared to a 3% increase for enzalutamide in the 12 months after ARPI initiation (P < .0001). Abiraterone was associated with greater increase in rates of acute heart failure, atrial fibrillation, acute kidney injury, urinary tract infections, sepsis, and pneumonia. ConclusionBy comparing the rate of hospitalization before vs. during treatment, real world analyses identified a 22% versus 3% increase in hospitalizations with abiraterone compared to enzalutamide respectively, despite being used in a younger population with less comorbid disease. Abiraterone was also associated with higher risk of infections, a novel finding.