A Study of Abiraterone Acetate Plus Low-Dose Prednisone Plus Androgen Deprivation Therapy (ADT) Versus ADT Alone in Newly Diagnosed Participants With High-Risk, Metastatic Hormone-Naive Prostate Cancer (mHNPC)

The purpose of this study is to determine if newly diagnosed (within previous 3 months) participants with metastatic (spread of cancer cells from one part of the body to another ) hormone-naive prostate cancer (mHNPC) who have high-risk prognostic factors will benefit from the addition of abiraterone acetate plus low-dose prednisone to androgen deprivation therapy (ADT; lutenizing hormone releasing hormone \[LHRH\] agonists or surgical castration).

This is a randomized (the treatment group is assigned by chance), double-blind (neither physician nor participant knows the treatment that the participant receives), placebo (an inactive substance that is compared with a drug to test whether the drug has a real effect in a clinical trial)-controlled study designed to determine the efficacy of abiraterone acetate plus low-dose prednisone in participants with mHNPC. The study consists of 4 parts: Screening Phase (that is, 28 days before study commences on Day 1); Double-blind treatment Phase (consists of 4-week dosing cycles wherein abiraterone acetate will be administered as 1,000 milligram \[mg\] plus 5 mg prednisone or only placebo orally); Follow-up Phase (every 4 months up to 60 months or until death, lost to follow up, withdrawal of consent or study termination) Open-label Extension (OLE) Phase. Participants in the Double-blind Treatment Phase will have the opportunity to enroll into the OLE Phase. The OLE Phase will allow participants to receive active drug (abiraterone acetate plus prednisone) until Long-term Extension (LTE) Phase for an additional period of up to 3 years. Participants will discontinue study treatment at disease progression or unacceptable toxicity unless, in the Investigator's opinion, it is deemed that the participants will continue to derive benefit from study treatment. Participants will be randomized in a 1:1 ratio to the active treatment group (abiraterone acetate 1000 mg daily plus prednisone 5 mg daily plus ADT) or the control group (ADT plus placebos).Efficacy will be evaluated primarily by overall survival and radiographic progression-free survival. Participants' safety will be monitored throughout the study.