Docetaxel Versus Cabazitaxel Post Abiraterone or Enzalutamide

Inclusion Criteria: * Diagnosis of histologically or cytologically confirmed prostate adenocarcinoma. * Metastatic disease. * Progressive disease (PD) while receiving AR targeted therapy with abiraterone acetate or enzalutamide by at least one of the following: * Progression in measurable disease (RECIST 1.1 criteria). Patient with measurable disease must have at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded). Each lesion must be at least 10 mm when measured by computed tomography (CT) \[CT scan thickness no greater than 5 mm\] or magnetic resonance imaging (MRI). Lymph nodes should be ≥ 15 mm in short axis. As defined by PCWG2, if lymph node metastasis is the only evidence of metastasis, it must be ≥ 20 mm in diameter when measured by spiral CT or MRI. Previously irradiated lesions, primary prostate lesion and bone lesions will be considered non-measurable disease, and/or * Appearance of 2 or more new bone lesions. They must be confirmed by other imaging modalities (CT; MRI) if ambiguous results (PCWG2), and/or * Rising PSA defined (PCWG2) as at least two consecutive rises in PSA to be documented over a reference value (measure 1) taken at least one week apart. The first rising PSA (measure 2) should be taken at least 7 days after the reference value. A third confirmatory PSA measure is required (2nd beyond the reference level) to be greater than the second measure and it must be obtained at least 7 days after the 2nd measure. If this is not the case, a fourth PSA measure is required to be taken and be greater than the 2nd measure. The third (or the fourth) confirmatory PSA should be taken within 4 weeks prior to randomization. * A PSA value of at least 2 ng/mL is required at study entry. * Effective castration (serum testosterone levels ≤0.5 ng/mL). * Prior AR targeted therapy (abiraterone acetate or enzalutamide) must be stopped at least 2 weeks before study treatment. * Signed written informed consent. Exclusion Criteria: Related to methodology: * Prior chemotherapy for prostate cancer, except estramustine and except adjuvant/neoadjuvant treatment completed \>3 years ago. Prior treatment with sipuleucel T immunotherapy is allowed at the condition patient did not received prior chemotherapy. No further anti-cancer therapy after the previous AR targeted therapy and before inclusion. * Less than 28 days elapsed from prior treatment with radiotherapy or surgery to the time of randomization. * Prior isotope therapy, whole bony pelvic radiotherapy, or radiotherapy to \>30% of bone marrow. * Adverse events (excluding alopecia and those listed in the specific exclusion criteria) from any prior anticancer therapy of grade \>1(National Cancer Institute Common Terminology Criteria \[NCI CTCAE\] v4.0) at the time of randomization. * Less than 18 years (or country's legal age of majority if the legal age is \>18 years). * Eastern Cooperative Oncology Group (ECOG) performance status \>1. * History of brain metastases, uncontrolled spinal cord compression, or carcinomatous meningitis or new evidence of brain or leptomeningeal disease. * Prior malignancy. Adequately treated basal cell or squamous cell skin or superficial (pTis, pTa, and pT1) bladder cancer are allowed, as well as any other cancer for which treatment has been completed ≥5 years ago and from which the patient has been disease-free for ≥5 years. * Participation in another clinical trial and any concurrent treatment with any investigational drug within 30 days prior to randomization. * Any of the following within 3 months prior to randomization: treatment resistant peptic ulcer disease, erosive esophagitis or gastritis, infectious or inflammatory bowel disease, diverticulitis, pulmonary embolism, or other uncontrolled thromboembolic event. * Acquired immunodeficiency syndrome (AIDS-related illnesses) or known HIV disease requiring antiretroviral treatment. * Any severe acute or chronic medical condition which could impair the ability of the patient to participate to the study or interfere with interpretation of study results, or patient unable to comply with the study procedures. * Patients with reproductive potential who do not agree to use accepted and effective method of contraception during the study treatment period and up to 6 months after the last administered dose. The definition of "effective method of contraception" will be based on the investigator's judgment. Related to study treatment * Known allergies, hypersensitivity or intolerance to prednisone. History of hypersensitivity to docetaxel or polysorbate 80. * Known history of mineralocorticoid excess or deficiency. * Unable to swallow a whole tablet or capsule * Inadequate organ and bone marrow function as evidenced by: 1. Hemoglobin \<10.0 g/dL 2. Absolute neutrophil count \<1.5 x 109/L 3. Platelet count \<100 x 109/L 4. AST/SGOT and/or ALT/SGPT \>1.5 x ULN; 5. Total bilirubin \>1.0 x ULN 6. Potassium \<3.5 mmol/L 7. Serum albumin \<3.0 g/dL 8. Child-Pugh Class B and C 9. Serum Creatinine ≤ 1.5 x ULN, * Contraindications to the use of corticosteroid treatment. * Symptomatic peripheral neuropathy grade \>2 (National Cancer Institute Common Terminology Criteria for Adverse Events \[NCI CTCAE\] v.4.0). * Clinically significant heart disease as evidenced by myocardial infarction, or arterial thrombotic events in the past 12 months, severe or unstable angina, or New York Heart Association (NYHA) Class III or IV heart disease or cardiac left ventricular ejection fraction (LVEF) measurement of \<50% at baseline.