Testosterone Revival Abolishes Negative Symptoms, Fosters Objective Response and Modulates Enzalutamide Resistance

Eligible patients will have metastatic CRPC with no disease related symptoms and progression on Androgen deprivation therapy and will have progressed post-treatment with abiraterone. Patients will continue on Androgen deprivation therapy with Luteinising Hormone Releasing Hormone agonist (i.e. Zoladex, Trelstar, Eligard or Lupron) or Luteinising Hormone Releasing Hormone antagonist (Degarelix) if not surgically castrated throughout the duration of the study to inhibit endogenous testosterone production. Patients will be randomized 1:1 and stratified based on duration of prior abiraterone acetate therapy (6 months or less or greater than 6 months). Patients randomized to BAT (Arm A) will receive intramuscular injections with either testosterone cypionate or testosterone enanthate at a dose of 400 mg every 28 days. This dose was selected based on data demonstrating that it produces an initial supraphysiologic serum level of T (i.e. \> 1500 ng/dL or 3-10 times normal level) with eugonadal levels achieved at the end of two weeks and near castrate levels after 28 days. Patients randomized to enzalutamide (Arm B) will receive daily oral dose of 160 mg. Each cycle is defined as 28 days. Patients will have Prostate-specific antigen level and symptoms assessment checked every cycle. Every 3 cycles patients will have repeat bone/CT scans to evaluate treatment response status. On CT scan, radiographic progression will be defined by RECIST criteria (i.e. \>20% increase in the sum of target lesions). On bone scan, radiographic progression will be defined by PCWG2 criteria as ≥ 2 new bone lesions. However, for the first reassessment scan only, patients should remain on study and have a confirmatory scan performed 12 weeks (3 cycles) later. If this confirmatory scan shows 2 or more additional new lesions, this defines progression. The date of progression is the date of the first reassessment bone scan. If the confirmatory scan does not show any additional new lesions, patient remains on study. If progression is observed on subsequent bone scans, a confirmatory scan is not required; the date of this bone scan is the date of progression. Patients with Prostate-specific antigen progression but with disease response or stable disease on imaging studies will remain on study until radiographic or other clinical progression criteria are met. Patients with radiographic disease progression will not receive continued BAT (arm A) or enzalutamide (arm B) and will be eligible for crossover to the opposite therapy. Patients on the BAT arm A can cross over to receive enzalutamide at time of progression or can choose to go off study and be treated with other standard of care treatments. Patients on the enzalutamide arm B will be allowed to cross-over to receive BAT or can choose to go off study and be treated with other standard of care treatments. Patients with clinical progression due to prostate cancer must meet study exclusion criteria to be permitted to cross-over to the opposite treatment. Patients with clinical progression due to pain from prostate cancer are not permitted to cross-over.