Inclusion Criteria:
* Biopsy proven prostate cancer and the diagnosis can be established through either prostate biopsy or biopsy of a metastatic lesion.
* No androgen deprivation therapy (ADT) with LHRH analog for more than 4 weeks after the diagnosis of metastatic prostate cancer. Prior ADT in the non-metastatic setting is allowed if it was given \> 2 years prior to the diagnosis of metastatic prostate cancer.
* Achieved \>50% PSA decline and \<4 ng/ml PSA after the run-in period.
* Adequate organ function with absolute neutrophil count \> 1000/l, Hb \> 10 g/dl, Platelet \> 100,000/l, Creatinine and liver enzymes within 1.5 folds of upper limits of normal.
* No uncontrolled arrhythmia; patients with h/o myocardia infarction or history of congestive heart failure, need to have estimated left ventricle ejection fraction above 40% either on echocardiogram or MUGA scan within 6 months of study enrollment.
* ECOG performance status 0-1.
* Non-sterilized men who are sexually active with a female partner of childbearing potential treated or enrolled on this protocol must agree to use adequate contraception prior to the study, for the duration of study participation, and for 6 weeks after last dose of ARSI or docetaxel administration.
* Ability to understand and the willingness to sign a written informed consent document or have a legally authorized representative sign on the subject's behalf. Stated willingness to comply with all study procedures and availability for the duration of the study.
Exclusion Criteria:
* Prior treatments with TAK-700/Orteronel, abiraterone, apalutamide or enzalutamide.
* Surgical castration.
* Documented liver or brain metastases
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to docetaxel (including any drugs formulated with polysorbate 80), or LHRH analog (e.g., leuprolide, triptorelin, relugolix, degarelix)
* Treatment with any investigational compound within 30 days prior to the first dose of study drugs.
* Diagnosis or treatment for another systemic malignancy within 2 years before the first dose of LHRH analog, or previously diagnosed with another malignancy \& have any evidence of residual disease. Patients with early-stage skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection.
* Uncontrolled inter-current illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
* Subjects with delayed healing of wounds, ulcers, and/or bone fractures.
