A031201 Castration Resistant Metastatic Prostate Cancer (PRO00001965)

About 1224 people will take part in this research study. Eligible patients will be assigned to one of two groups. Neither the participant nor their study doctor can choose the group they will be in. Participants will have a one in two chance of being placed in either group. Those assigned to Group 1 (often called “Arm A”) will take enzalutamide by mouth once daily every morning. Those assigned to Group 2 (often called “Arm B”) will take enzalutamide and prednisone by mouth every morning, and abiraterone and prednisone by mouth every evening. Participants in both arms will receive a 4-week supply of enzalutamide with or without abiraterone and prednisone every 28 days in this study. This 28 day period is called a cycle. The cycle will be repeated for as long as the participant’s prostate cancer is responding to the medication. Study drug doses should be taken as close as possible to the same time each day. If, for any reason, a dose is missed, skip that dose and continue taking the drug as prescribed. Participants will be asked to record the day, number of pills taken, and time of each dose of enzalutamide and/or abiraterone and prednisone on a medication calendar. Participants should bring the calendar and pill bottles to their clinic visits. Participants will have a CT scan or MRI of their abdomen and pelvis, a CT scan or X-ray of their chest, and a bone scan every 8 weeks for the first 6 months of treatment, and then every 12 weeks.