In this placebo-controlled , double-blind , randomised phase 3 study , 1088 asymptomatic or mildly symptomatic patients with chemotherapy-naive prostate cancer stratified by Eastern Cooperative Oncology performance status ( 0 vs 1 ) were randomly assigned with a permuted block allocation scheme via a web response system in a 1:1 ratio to receive either abiraterone acetate ( 1000 mg once daily ) plus prednisone ( 5 mg twice daily ; abiraterone acetate group ) or placebo plus prednisone ( placebo group ) .