CABAzitaxel With or Without Prednisone in Patients With Metastatic CAstration REsistant Prostate Cancer Progressed During or After a Previous Docetaxel-based Chemotherapy

Patients will be randomly assigned (1:1) to receive either: Arm A Cabazitaxel 25 mg/m² intravenously (Day 1) every 3 weeks, plus prednisone 10 mg orally given daily. Premedication must be administered according to Cabazitaxel Package Insert. Arm B Cabazitaxel 25 mg/m² intravenously (Day 1) every 3 weeks, without daily prednisone. Premedication must be administered according to Cabazitaxel Package Insert. Each patient will be treated until radiological disease progression, unacceptable toxicity, or patient refusal. Patients will be followed through subsequent therapy lines of treatments until death or the study cut-off, whichever comes first. Every effort will be made to administer the full dose regimen to maximize dose-intensity. Dose reduction and/or treatment delay and/or treatment discontinuation are planned in case of severe toxicity. If toxicity occurs, dose of Cabazitaxel can be reduced to 20 mg/mq in both arms. If a second dose reduction is required the patient should be withdrawn from study. Prednisone doses should not be delayed or modified or stopped (unless there is a contraindication to continue, the decision will be let to the investigator's discretion). In case a dose reduction is required, cabazitaxel dose cannot be re-escalated. Prophylactic use of G-CSF is allowed, as per EORTC / ASCO guidelines and according to physician judgment. Patients experiencing neutropenia G 3-4 have to receive G-CSF in prophylaxis in subsequent cycles. Primary Objective(s) To evaluate whether cabazitaxel alone is non inferior in terms of radiographic PFS with respect to cabazitaxel plus daily prednisone in patients with castration resistant prostate cancer Secondary Objective(s) Safety in the two treatment arms; Health-Related Quality of Life (HRQL) and pain; Objective Response Rate (ORR) according to Response Evaluation Criteria In Solid Tumors (RECIST 1.1); Biochemical response (assessed considering PSA decrease ≥50% and waterfall plot results); Time to PSA Progression (TTPP); Radiographic Time to Progression (rTTP); Overall Survival (OS); Association of Overall l Survival (OS), Progression Free Survival (PFS) and Objective Response Rate (ORR) with AR-V7 and RB status in circulating tumor cells assessed at flow-cytometry; Time to Skeletal-Related Event (SRE); Primary end Point Radiographic Progression-Free Survival (rPFS). Secondary end points Safety in the two treatment arms; Health-Related Quality of Life HRQL and pain; Objective Response Rate (ORR) according to Response Evaluation Criteria In Solid Tumors (RECIST 1.1); Biochemical response (PSA decrease ≥50%, waterfall plot); Time to PSA Progression (TTPP); Radiographic Time To Progression (rTTP); Overall Survival (OS); Association of Overall Survival (OS), Progression Free Survival (PFS) and Objective Response Rate (ORR) with AR-V7 and RB status in circulating tumor cells by the use of a DNA test; Time to Skeletal-Related Event (SRE).