Study of Abiraterone Acetate in Participants With Metastatic Castration-Resistant Prostate Cancer (mCRPC), Chemo-Naive, Who Received a Prior Diethylstilbestrol Therapy

The purpose of this study is to evaluate the efficacy, based on prostate-specific antigen (PSA) progression, of abiraterone acetate in participants with metastatic (spread of cancer cells from one part of the body to another) castration (any action, surgical, chemical, or otherwise, by which a male loses the functions of the testes) resistant prostate cancer (cancer in prostrate; a gland that makes fluid that aids movement of sperm) (mCRPC), chemo-naive (treatment of cancer is not done using drugs), who received a prior diethylstilbestrol therapy (DES).

This is a Phase 2, multinational (when medical research study takes place in more than one country), multicenter (when more than one hospital or medical school team work on a medical research study), open-label (all people know the identity of the intervention), and single arm study to determine benefits of abiraterone acetate and low-dose prednisone to androgen deprivation therapy (ADT) in mCRPC participants who failed to prior DES therapy. The study will consist of a Screening Phase of up to 28 days before enrollment; a PSA Evaluation Phase; and a Follow-up Phase of up to 24 months. Each cycle of abiraterone therapy will be of 28 days. Participants will receive 1000 milligram (mg) abiraterone acetate orally once daily plus prednisone 5 mg orally once daily plus stable regimen of ADT (luteinizing hormone-releasing hormone \[LHRH\] agonists) as per Investigator's discretion. Treatment will continue until PSA progression, clinical progression, consent withdrawal, or the occurrence of unacceptable toxicity. Efficacy will primarily be assessed by time to PSA progression. Participants' safety will be monitored throughout the study.

Eligibility Criteria:
Inclusion Criteria:

* Histologically or cytologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell histology
* Prior therapy with diethylstilbestrol (DES) for castration resistant prostate cancer. Participants should demonstrate evidence of progression on DES or evidence of grades 3/4 toxicities on DES
* Metastatic disease documented by positive bone scan or metastatic lesions on computerized tomography (CT) or magnetic resonance imaging (MRI)
* May have received prior androgen blockage (bicalutamide or flutamide) but must have been discontinued for least 28 days
* Ongoing androgen deprivation therapy (ADT) (luteinizing hormone-releasing hormone \[LHRH\] agonist or orchiectomy), with serum testosterone level of less than 50 nanogram per deciliter (1.7 nanomole per liter) and eligible participants must maintain ADT

Exclusion Criteria:

* Active infection or other medical condition that would make prednisone use contraindicated
* Any chronic medical condition requiring a higher systemic dose of corticosteroid than 5 milligram (mg) prednisone per day
* Pathological finding consistent with small cell carcinoma of the prostate
* Known brain metastasis
* Has had prior cytotoxic chemotherapy or biologic therapy for the treatment of metastatic castration-resistant prostate cancer (mCRPC)