LAUSR

610Background: Growing evidence have shown promise for targeting programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) signaling in several tumors. However, the role of PD-L1 expression in colorectal cancer (CRC) tumor cells and its interaction with other clinicopathologic factors remain elusive. Methods: We constructed a tissue microarray with paraffin-embedded primary colon cancer tissue (n=103; stage I, 22; II: 44; III: 37). Expression levels of biomarkers (PD-L1, EGFR, p53, Ki67, LEF1, VEGF, COX2, MMR – by IHC, and MiR-34a - by in situ hybridization), clinicopathologic variables and clinical outcomes were investigated. H-score evaluation of PD-L1 was performed. Tumors with an H score >55, derived using Cutoff Finder, were considered PD-L1 positive for use in Kaplan-Meier survival analysis with log-rank test and in Cox regression models for recurrence-free survival (RFS) and overall survival (OS). Results: Median follow-up time for the entire cohort was 4.7 years (range 0.1-20.8). Positive PLD1 w...