Abiraterone acetate (AA) is a prodrug of abiraterone, an irreversible inhibitor of 17α hydroxylase/C17, 20-lyase (cytochrome P450c17 [CYP17]).The inhibition of CYP17A1 blocks androgen and cortisol synthesis. AA has a pharmacodynamic potential to reduce cortisol excess and it has never been tested before in Cushing's syndrome.