634 Background: TAS-102 is comprised of an antineoplastic thymidine-based nucleoside analog, trifluridine, and a thymidine phosphorylase inhibitor, tipiracil hydrochloride. Efficacy and safety of TAS-102 in patients with metastatic colorectal cancer refractory/intolerant to standard therapies were evaluated in the RECOURSE trial. Original results of RECOURSE based on the cut-off date of January 24, 2014, in which 72% of mortality events had occurred, demonstrated a significant improvement in overall survival (OS) with TAS-102 vs placebo. Here we report results of an updated survival analysis from RECOURSE and a retrospective analysis of OS outcomes based on a clinical prognostic risk index. Methods: Patients were randomized 2:1 to receive TAS-102 or placebo. Study treatment continued until disease progression, death, or unacceptable toxicity. The primary endpoint was OS; final survival data were collected on October 8, 2014. A clinical OS prognostic risk score was assessed to evaluate OS effect in patient...