Abstract 4031: Different expression of programmed death 1 (PD1) and its ligand (PD-L1) in esophageal and gastric cancer

Background: Prognosis of gastric and esophageal cancer remains poor. Improvements in gastric and esophageal cancer treatments are urgently needed. Programmed cell death 1 receptor (PD1) and its ligand 1 (PD-L1) are known to interact with T cells promoting epithelial cancer tolerance. Several therapeutic monoclonal antibodies blocking this interaction are reaching the clinical praxis. Therefore it is relevant to investigate the role of these biomarkers in different types of malignancy. Methods: Four different copies of tissue microarrays (TMA), each including healthy mucosa (n = 74) and a total of 241 clinically annotated malignancies of the esophagus (n = 80) and stomach (n = 161) were constructed and stained with PD1, PD-L1, and CD8 specific reagents. Results: Interestingly, only two cancer samples out of the 241 specimens investigated weakly expressed PD-L1. None of the normal mucosa epithelial cells expressed PD-L1. Stromal PD1 expression correlated with infiltration by CD8+ lymphocytes (rho = 0.4; P