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