TPS405 Background: The most significant morbidity of prostate cancer (PC) is bone metastasis (BM). More than 90% of patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) have radiologic evidence of BM, which are a major cause of death, disability, decreased QoL, and increased treatment cost. Unlike deaths from many other types of cancer, deaths from PC are often due to bone disease and its complications. In vitro data demonstrate a role for taxanes in the regulation of osteoclast formation and function, with a decreased resorption activity. ÊSTAMPEDE study has shown a strong clinical benefit, in term of OS, PFS and skeletal related events (SREs) delay compared with ADT alone, in metastatic hormone-sensitive pts treated with docetaxel (DOC) and ADT. TROPIC Study has shown that cabazitaxel (CBZ) prolongs OS regardless of DOC response in responder, resistant and refractory pts. Some data are available on pain progression, pain response and ECOG PS deterioration but in a unselected ITT population with a low prevalence of only BM disease at baseline, 25% of men had visceral metastasis. No data are available on effects of CBZ on BM and his direct impact on quality of life, bone turnover markers and time to the first SRE events. The aim of CaBone phase II study is to investigate, specifically, the effects on bone disease, bone turnover and on the bone related quality of life of CBZ in mCRPC pts with skeletal involvement without visceral disease. Methods: CaBone is a single arm, prospective, open label, multi center, phase II - GOIM - cooperative study of CBZ 25 mg/m2 q21 plus daily PDN (10 mg) in mCRPC pts with bone mets without visceral disease progressed during or after DOC treatment. Primary endpoint is Bone PFS according to PCWG2 while the Secondary are related on Evaluation of bone disease: Time to SRE, Time to Bone Pain Progression, Bone Pain Response, Time to opiate use for cancer-related pain, Time to deterioration in ECOG PS, Evaluation of Quality of Life and Functional status, Safety and centralized bone turnover markers: ALP, Bone ALP , LDHÊ, Serum CTx, iPTH, 1.25 (OH)2ÊD3. 107 subjects will be enrolled in CaBone study. CaBone is partially supported by Sanofi Genzyme. Clinical trial information: 2016-001253-41.