Study of Abiraterone Acetate Without Exogenous Glucocorticoids in Men With Castration-resistant Prostate Cancer

Participants will be treated with abiraterone acetate (AA) in 28-day cycles. Participants will be monitored (weekly for the first two cycles, then on Day 1 of each subsequent cycle) for symptoms of persistent or severe mineralocorticoid excess (including hypertension, hypokalemia). For participants who experience symptoms of persistent or severe hypertension or hypokalemia as detailed in the above schema, prednisone 5 mg by mouth twice daily will be added. We will monitor for other symptoms of AA toxicity to include fluid retention and fatigue. For participations who tolerate AA monotherapy without the addition of prednisone to manage symptoms of persistent or severe mineralocorticoid excess, prednisone 5 mg by mouth twice daily will be added at Prostate Specific Antigen (PSA) progression. Participants will be continued on study until symptomatic or radiographic progression or taken off study for another reason as detailed in protocol.