This is a randomized (individuals will be assigned by chance to study treatments), double-blind (individuals and study personnel will not know the identity of study treatments), 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 in approximately 1,000 medically or surgically castrated male patients with metastatic CRPC who have shown tumor progression and are asymptomatic or mildly symptomatic. The study period will consist of screening, treatment, and follow-up phases. Patients will receive study treatment (abiraterone acetate or placebo) plus prednisone until radiographic progression of disease and/or unequivocal clinical progression. Efficacy evaluations will be performed throughout the treatment period and safety will be assessed until 30 days after the last dose of abiraterone acetate. throughout the study. Follow-up will continue for up to 60 months (5 years) or until the patient dies, is lost to follow-up, or withdraws informed consent. At the interim analysis of overall survival (OS; 43% of death events), the independent data monitoring committee (IDMC) reviewed the efficacy and safety data and concluded that all of the data pointed to a significant advantage for patients in one arm of the study compared with the other arm thereby unanimously recommending unblinding the study and allowing crossover from the placebo arm to active therapy. Patients currently receiving placebo will be offered crossover therapy to abiraterone acetate. Treatment for patients who were originally randomized to the abiraterone acetate treatment group will not change. Patients will be discontinued from long term follow-up at the time of the Clinical Cut-Off Date for Final Analysis (CCO-FA); however, patients still receiving treatment with abiraterone acetate at the CCO-FA will be offered to receive continued treatment for an additional period of up to 3 years or until disease progression or unacceptable toxicity. For these patients, safety assessment will be performed while continuing treatment, and for 30 days after the last dose of abiraterone acetate.
