253 Background: Abiraterone acetate (AA) provided a survival advantage compared to placebo in patients (pts) with castration resistant prostate cancer (CRPC) who had received docetaxel (de Bono JS et al, NEJM 2011). The present retrospective study is aimed to assess safety and clinical outcome in an unselected CRPC population which received AA in a named patient program (NPP). Methods: We retrospectively reviewed the clinical records of all pts treated with AA for CRPC by NPP in our institutions. All pts have been previously treated with a docetaxel-based first-line chemotherapy and received the standard AA dose of 1,000 mg daily plus prednisone 10 mg daily. For each pt we recorded the pre- and post-AA clinical history, the AA treatment details toxicities and clinical outcomes. Results: To date we have collected a consecutive series of 245 pts from 18 Italian hospitals. The median age was 73 (range 45 to 91). The median baseline prostate-specific antigen (PSA) level was 100 ng/ml (range 0.33->100.000); 79% of the pts had bone metastases, while nodal, lung and liver metastases were observed in 52%, 9%, and 7% of the pts, respectively. The median duration of AA treatment was 5 months (range, 1 to 26). Grade 3 to 4 toxicities were anemia (11 pts), fatigue (nine pts), bone pain (four pts), constipation (two pts), thrombocytopenia (two pts), nausea (one pt), diarrhea (one pt), dyspnea (one pt), edema (one pt), hypertension (one pt), hyperbilirubinemia (one pt), and hypokaliemia (one pt). A PSA reduction of more than 50% was observed in 50.9% of the pts. The median progression-free survival (PFS) and overall survival (OS) were 6 months and 15 months, respectively; the 1 year PFS and OS rates were 24.3% and 56.9%, respectively. Conclusions: Our results have confirmed the safety and efficacy of AA in an unselected population of pts with pre-treated CRPC outside clinical trials and provided further support concerning the good safety profile of the drug.