This is a single arm two-site study of 37 men with unfavorable prostate cancer (defined as having a single high risk factor). Patients will concurrently initiate 6 months of standard-of-care GNRH agonist therapy and once daily abiraterone acetate/prednisone. After 2 months of lead-in hormonal treatment, definitive standard-of-care prostate/seminal vesicle radiotherapy will be delivered, to a total dose of 75-80 Gy.