Impact of Abiraterone Therapeutic Drug Monitoring on Cortisol as a Surrogate Biomarker of CYP17 Inhibition in Metastatic Prostate Cancer Treatment

BACKGROUND: Prostate cancer is driven by androgen receptor activation caused by (dihydro)testosterone. Abiraterone, which is used against metastatic castration-resistant prostate cancer (mCRPC), improves survival by irreversibly inhibiting CYP17 to reduce androgen and cortisol synthesis. As such, cortisol is a potential biomarker for androgen suppression. This study assessed the impact of pharmacokinetically (PK)-guided interventions after therapeutic drug monitoring (TDM) of abiraterone on cortisol plasma concentrations as a biomarker for CYP17 inhibition in patients with mCRPC. METHODS: In this retrospective cohort study, patients with mCRPC receiving abiraterone with TDM based on abiraterone plasma concentrations were compared with a historical cohort receiving standard care. The primary end point was adequate CYP17 inhibition, defined as cortisol plasma concentration