Safety and Efficacy of Oral Testosterone Undecanoate Followed by Enzalutamide as Therapy for Men With Metastatic Castrate Resistant Prostate Cancer

Inclusion Criteria:

* Patient has the ability to understand and willingness to sign a written informed consent document.
* Patient is a male aged 18 years or older.
* Patient has histologically-confirmed adenocarcinoma of the prostate
* Patient has an Eastern Cooperative Oncology Group (ECOG) performance status of ≤2 (as defined in Appendix A: Performance Status Criteria;
* Patient has evidence of metastatic, measurable disease by CT scan. Measurable disease is defined by RECIST 1.1 as at least one measurable lesion ≥10mm by CT scan
* Patient is progressing on continuous androgen ablative therapy (either surgical castration or LHRH agonist/antagonist)
* Patient has documented castrate level of serum testosterone (\<50 ng/dl)
* Patient is progressing on luteinizing hormone-releasing hormone (LHRH) agonist/antagonist plus anti-androgen or abiraterone for CSPC. (Note: Must be off anti-androgen or abiraterone for 4 weeks prior to first treatment with OT.) LHRH (luteinizing hormone-releasing hormone)
* Patient has had prior docetaxel for CSPC. Note: Docetaxel is permitted if ≤ 6 doses were given in conjunction with first-line androgen deprivation therapy and \>6 months since last dose of docetaxel. (CSPC-castrate sensitive prostate cancer)
* Patient is currently taking prednisone and cannot be weaned entirely off. Note: Patient's dose must be maintained on lowest stable dose that relieves symptoms. Patient is receiving prednisone in conjunction with abiraterone acetate must be weaned off prednisone if possible prior to starting OT.
* Patient has had a rising PSA on two successive measurements at least two weeks apart.
* Patient agrees to continue on castrating therapy throughout OT treatment.
* Patient's screening lab values are within the following parameters:

  1. Absolute neutrophil count (ANC) ≥ 1500 cells/mm3 (1.5 ×109/L)
  2. Platelet count ≥ 100,000 platelet/mm3 (100 ×109/L)
  3. Hemoglobin ≥ 9 g/dL
  4. Serum creatinine \< 2.5 times ULN
  5. Bilirubin \< 2.5 times institutional upper limit of normal (ULN)
  6. Aspartate aminotransferase (AST) and Alanine Aminotransferase (ALT) \< 2.5 times ULN
* Patient has had surgery, has completed at least 4 weeks of recovery and has no persistent toxicity \> grade 1.

Exclusion Criteria:

* Patient has pain due to metastatic prostate cancer requiring opioid analgesics.
* Patient has had prior treatment with any agent for metastatic castration-resistant prostate cancer. (Includes docetaxel, cabazitaxel, anti-androgen, abiraterone, or investigational agents)
* Patient requires urinary catheterization for voiding due to obstruction secondary to prostatic enlargement thought to be due to prostate cancer or benign prostatic hyperplasia. Note: Patients with indwelling catheter/suprapubic catheter to relieve obstruction are eligible.
* Patient has evidence of disease in sites or extent that, in the opinion of the investigator, would put the patient at risk from therapy with testosterone (e.g. femoral metastases with concern over fracture risk, epidural spinal metastases with concern over spinal cord compression, lymph node disease with concern for ureteral obstruction).
* Patient has evidence of disease in sites or extent that, in the opinion of the investigator, would put the patient at risk from therapy with testosterone (e.g. femoral metastases with concern over fracture risk, epidural spinal metastases with concern over spinal cord compression, lymph node disease with concern for ureteral obstruction).
* Patient has active uncontrolled infection, such as HIV/AIDS or chronic hepatitis B or untreated chronic hepatitis C.
* Patient has had prior history of a thromboembolic event within the past two years and not currently on systemic anticoagulation.
* Patient is on Coumadin. Note: If anticoagulation therapy is mandatory, patient must be switched to an alternative medication) Patients receiving anticoagulation therapy with warfarin, rivaroxaban or apixaban are not eligible for study. \[Patients on enoxaparin or edoxaban are eligible for study. Patients on warfarin, rivaroxaban or apixaban, who can be transitioned to enoxaparin prior to starting study treatments, will be eligible.
* Patient has hematocrit \>50%, untreated severe obstructive sleep apnea, uncontrolled or poorly controlled heart failure \[per Endocrine Society Clinical Practice Guidelines\].