Treatment switching between Enzalutamide and Abiraterone Acetate and time to oral opioid initiation in castration-resistant prostate cancer patients

Abstract

Background and aims: Enzalutamide (ENZ) and Abiraterone Acetate (AA) are both first-line treatments for castration-resistant prostate cancer (CRPC). CRPC patients may switch from ENZ to AA or from AA to ENZ, if they do not respond well to the treatment, or experience intolerable side effects. This study examine treatment switching from ENZ to AA or from AA to ENZ, while investigating death as a competing risk. Whether ENZ compared to AA was associated with a longer time to starting oral opioids was also investigated.

Methods: An active comparator new-user design was used to identify 1406 men diagnosed with CRPC who received ENZ and AA using the Surveillance, Epidemiology, and End Results-Medicare Linked Database from 2012 to 2016. Inverse probability treatment weights (IPTW)-adjusted Fine-Gray competing risk models were used to compare the switching drugs and time-to-first use of oral opioids after initiating ENZ and AA.

Results: Most patients (61 %) received AA, while 39 % received ENZ. Overall, ENZ demonstrated a significant reduction in the Sub-distribution Hazard Ratio (SHR) for switching treatment (IPTW-adjusted SHR 0.63; 95 % CI, 0.54-0.73; P < 0.001), indicating a decrease in treatment switching compared to AA. Cumulative incidence curves revealed substantial differences in switching patterns over time (Gray's test, p < 0.001). For time-to-first oral opioid use, the IPTW-adjusted SHR when comparing ENZ to AA was 0.95 (95 % CI, 0.83-1.09; P = 0.48), showing no significant difference between the two groups.

Conclusion: Patients who began their treatment with ENZ exhibited a substantially lower hazard of switching to AA when compared to those who started with AA.

Keywords: Abiraterone Acetate; Enzalutamide; Oral opioids; Prostate cancer; Surveillance, Epidemiology, and End Results-Medicare linked database.