LAUSR

50Background: Although immune checkpoint inhibitors have demonstrated promising results in melanoma and lung cancer, their effects on gastrointestinal cancer are still under investigation. Understand the prognostic effect of PDL1 expression, infiltration by CD8+ and CD3+ T cells in gastric cancer (GC) might help the identification of candidate patient who might benefit from immunotherapy. Methods: Immunohistochemistry were performed on a tissue microarray including 1,014 GC specimens with PD-L1 antibodies. Immune cell markers CD3 and CD8 were also stained and the quantitative differences were calculated using automated image analysis. Results: 37.8% of the cases showed a membranous PD-L1 expression in tumor cells and 74.9% in tumor infiltrating immune cells. GC patients with high level PDL1 expression in tumor cells or in immune cells were both associated with better survival compared with those with negative expression (5-year OS, 61% vs. 48%, P = 0.000, and 55% vs. 45%, P < 0.0001, respectively). As con...