The purpose of this study is to describe the rate of 3-year progression free survival in men with recurrent PSA-only disease after prostatectomy, who receive combined apalutamide (ARN-509) and standard ADT with salvage radiation therapy followed by docetaxel, ADT, and apalutamide, AND who have had testosterone recovery to >100 ng/dl at 36 months. The hypothesis is that AR inhibition with apalutamide added to standard salvage external beam radiation with androgen deprivation therapy, as well as the addition of 6 cycles of docetaxel, will further prolong progression free survival.