Inclusion Criteria:

          -  Pathologically (histologically) proven diagnosis of prostate adenocarcinoma;
             prostatectomy must have been performed within 10 years prior to Step 1 registration
             and any type of radical prostatectomy is permitted, including retropubic, perineal,
             laparoscopic or robotically assisted

          -  Post-prostatectomy patients with a detectable serum PSA (≥ 0.1, but ≤ 1.0 ng/mL) at
             study entry (within 90 days of Step 1 registration) and at least one of the following:

               -  Gleason score 7-10 (International Society of Urological Pathology [ISUP] grade
                  group 2 to 5)

               -  ISUP grade group:

                    -  Grade Group 1: Gleason score ≤ 6,

                    -  Grade Group 2: Gleason score 3 + 4 = 7,

                    -  Grade Group 3: Gleason score 4 + 3 = 7,

                    -  Grade Group 4: Gleason score 8,

                    -  Grade Group 5: Gleason scores 9 and 10

               -  >= T3a disease

               -  Persistent elevation of PSA after prostatectomy measured within 90 days after
                  surgery (PSA never became undetectable) of > 0.04 but < 0.2 ng/mL (PSA nadir)

          -  pN0 or pNx

          -  History/physical examination within 90 days prior to Step 1 registration

          -  Karnofsky performance status of 70-100 within 90 days prior to Step 1 registration

          -  Surgical formalin-fixed paraffin-embedded (FFPE) specimen must be available for
             submission to GenomeDx for genomic analysis on Decipher GRID platform; Note: if
             Decipher results have already been obtained, in lieu of tissue, results must be
             submitted to GenomeDx for validation

          -  Prior androgen deprivation therapy (luteinizing hormone-releasing hormone [LHRH]
             agonist and/or non-steroidal anti-androgen) is allowed if discontinued at least 90
             days prior to Step 1 registration and given for ≤ 90 days duration

               -  For example: patients on prior LHRH analogs (post-prostatectomy), the
                  discontinuation date should be calculated based on the expected duration of the
                  sustained release injection, not simply the injection date of the drug; for
                  instance, if a 22.5 mg sustained release dose of leuprolide acetate is given (3
                  month duration), then the expected duration of such a dose would be 90 days after
                  the injection date; for a 7.5 mg leuprolide (1 month duration), the
                  discontinuation date would be 30 days after the injection date

               -  Please note: finasteride or dutasteride must be stopped before treatment starts
                  but prior usage will not affect eligibility

          -  Hemoglobin ≥ 9.0 g/dL, independent of transfusion and/or growth factors within 90 days
             prior to Step 1 registration

          -  Platelet count ≥ 100,000 x 10^9/uL independent of transfusion and/or growth factors
             within 90 days prior to step 1 registration

          -  Serum albumin ≥ 3.0 g/dL within 90 days prior to Step 1 registration

          -  Glomerular filtration rate (GFR) ≥ 35 mL/min estimated by Cockcroft-Gault or measured
             directly by 24 hour urine creatinine within 90 days prior to Step 1 registration

          -  Serum total bilirubin ≤ 1.5 x upper limit of normal (ULN) (Note: in subjects with
             Gilbert's syndrome, if total bilirubin is > 1.5 x ULN, measure direct and indirect
             bilirubin and if direct bilirubin is ≤ 1.5 x ULN, subject is eligible) within 90 days
             prior to Step 1 registration

          -  Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) < 2.5 x ULN within
             90 days prior to Step 1 registration

          -  Testosterone > 50 ng/dL within 90 days prior to Step 1 registration

          -  Concomitant medications known to lower the seizure threshold discontinued or
             substituted at least 4 weeks (30 days) prior to Step 1 registration.

          -  The patient must agree to use a condom (even men with vasectomies) and another
             effective method of birth control if he is having sex with a woman of childbearing
             potential or agree to use a condom if he is having sex with a woman who is pregnant
             while on study drug and for 3 months following the last dose of study drug

          -  The patient must agree not to donate sperm during the study treatment and for 3 months
             after receiving the last dose of study drug

          -  The patient or a legally authorized representative must provide study-specific
             informed consent prior to study entry

        Exclusion Criteria:

          -  Definitive clinical, radiologic, or pathologic evidence of metastatic disease (M1) or
             lymph node involvement (N1)

          -  Prior invasive malignancy (except non-melanomatous skin cancer, carcinoma in situ of
             the male breast, penis, oral cavity, or stage Ta of the bladder, or stage I completely
             resected melanoma) unless disease free for a minimum of 2 years

          -  Prior systemic chemotherapy for the study cancer; note that prior chemotherapy for a
             different cancer is allowable

          -  Prior radiotherapy to the region of the study cancer that would result in overlap of
             radiation therapy fields

          -  History of any of the following:

               -  Seizure or known condition that may pre-dispose to seizure (e.g. prior stroke
                  within 1 year prior to Step 1 registration)

               -  History of documented inflammatory bowel disease

               -  Transmural myocardial infarction within the last 4 months prior to Step 1
                  registration.

               -  Unstable angina and/or congestive heart failure requiring hospitalization within
                  the last 6 months prior to Step 1 registration

               -  History of any condition that in the opinion of the investigator, would preclude
                  participation in this study

          -  Current evidence of any of the following:

               -  Known gastrointestinal disorder affecting absorption of oral medications

               -  Active uncontrolled infection (eg, human immunodeficiency virus [HIV] or viral
                  hepatitis)

               -  Uncontrolled hypertension

               -  Any current condition that in the opinion of the investigator, would preclude
                  participation in this study

          -  Prior whole gland ablative therapy (i.e. cryoablation or high intensity focused
             ultrasound [HIFU]) for prostate cancer is not allowed

          -  HIV positive with CD4 count < 200 cells/microliter within 30 days prior to
             registration

          -  HIV patients under treatment with highly active antiretroviral therapy (HAART) within
             30 days prior to registration regardless of CD4 count. (Note: HIV testing is not
             required for eligibility for this protocol as it is self-reported.)

          -  For patients who have not undergone prior Decipher analysis, submission of the
             specimen to GenomeDx should be as soon as possible after study registration (Step 1)
             as these results can take up 21 days after the specimen is received at GenomeDx; Step
             2 registration must occur within 6 weeks (42 days) of Step 1 registration; if Decipher
             results have already been obtained, in lieu of tissue, results must be submitted to
             GenomeDx for validation