The purpose of this study is to demonstrate the safety and effectiveness of abiraterone acetate when co-administered with prednisone in patients with chemo-naive metastatic castration resistant prostate Cancer (mCRPC).

This is a multinational, multicenter, randomized (the study drug is assigned by chance), double-blind (neither physician nor patient knows the treatment that the patient receives), placebo-controlled (an inactive substance that is compared with a drug to test whether the drug has a real effect in a clinical trial) study. All patients will be randomly assigned in a 1:1 ratio between the abiraterone acetate group (abiraterone acetate and prednisone) and the placebo group (placebo and prednisone). The study will consist of a screening phase (within 28 days prior randomization on Cycle 1, Day 1), a treatment phase (28-day cycles until disease progression), and a follow-up phase (all patients will be contacted for every 3 months up to Month 60, focusing primarily on survival status). Patients will receive either abiraterone acetate 1,000 mg daily and prednisone 5 mg twice daily or placebo and prednisone 5 mg twice daily.

Inclusion Criteria:

• Has a confirmed diagnosis of adenocarcinoma of the prostate with evidence of metastatic disease
• Prostate cancer progression documented by PSA progression or radiographic progression
• Asymptomatic or mildly symptomatic from prostate cancer
• Surgically or medically castrated, with testosterone levels of <50 ng/dL
• Previous anti-androgen therapy and progression after withdrawal
• ECOG performance status score of 0 or 1
• If opiate analgesics for cancer-related pain, treatment must not be administered within 4 weeks of Cycle 1 Day 1
• If radiation therapy for treatment of the primary tumor is given, treatment must not be administered within 6 weeks of Cycle 1 Day 1
• If previously treated with ketoconazole for prostate cancer, duration of treatment must not be greater than 7 days
• Life expectancy of at least 6 months

Exclusion Criteria:

• Active infection or other medical condition that would make prednisone (corticosteroid) use contraindicated
• Any chronic medical condition requiring a higher dose of corticosteroid than 5 mg prednisone twice daily
• Pathological finding consistent with small cell carcinoma of the prostate
• Liver or visceral organ metastasis, brain metastasis, and other malignancy, except non-melanoma skin cancer, with a 30% probability of recurrence within 24 months
• Prior cytotoxic chemotherapy or biologic therapy for the treatment of metastatic castration-resistant prostate cancer (mCRPC)
• Radiation or radionuclide therapy for treatment of mCRPC
• Uncontrolled hypertension, patients with a history of hypertension are allowed provided blood pressure is controlled by anti hypertensive treatment
• History of pituitary or adrenal dysfunction