A Study of JNJ-56021927 (ARN-509) and Abiraterone Acetate in Participants With Metastatic Castration-Resistant Prostate Cancer

This is a multicenter, open-label (participants will know the identity of study drug received) study in participants with Metastatic Castration-Resistant Prostate Cancer (mCRPC). The study is a single sequence design (ie, all participants will take abiraterone acetate + prednisone \[AAP\] once daily on Days 1-7 of Treatment Cycle 1 and then proceed with combined daily intake of AAP+JNJ-56021927 from Treatment Cycle 1, Day 8 through to the end of treatment \[ie, for up to an expected duration of approximately 18 months\] and will be conducted as two cohorts (group of participant's). The study will consist of a 28-day screening phase to determine eligibility, an open-label treatment phase consisting of 28-day treatment cycles, and a 30-day follow-up phase for collection of adverse events (AE) after last dose of study drug. Participants will have blood samples collected during the study to evaluate pharmacokinetics, safety, and antitumor activity (PSA). Participant safety will also be monitored by the collection of adverse events. Imaging assessments for disease evaluation will be planned at discretion of the Investigator. Once all participants have completed study treatment up to Cycle 3 Day 1, a data cutoff is planned to evaluate the short term safety profile of the combination and to complete the PK analysis up to the cutoff date. All participants will continue on study (ie, to receive treatment) until disease progression, withdrawal of consent, lost to follow-up, or the occurrence of unacceptable toxicity. The end of the study is defined when all participants have completed treatment. Participant's safety will be monitored throughout the study.