Descriptive Study of Tumor Immune Microenvironment and Epstein-Barr Virus Infection in Gastric Adenocarcinoma

Introduction. The Cauca region, in Colombia, has a high incidence of gastric cancer and there are few studies describing tumor microenvironment in gastric cancer samples obtained from this geographic region.
Aim. The aim of this study was to describe the infiltration of CD3+, CD8+ T cells, the expression of programmed death-1 (PD-1) and programmed death ligand 1 (PD-L1), and Epstein-Barr virus infection in biopsies from Cauca patients with advanced intestinal-type gastric adenocarcinoma.
Methodology. This is a descriptive cross-sectional study of 24 gastrectomy samples out of 48 samples analyzed. Expression of CD3, CD8, PD-1, and PD-L1 was analyzed using immunohistochemistry, and infection by Epstein-Barr virus was analyzed by Epstein-Barr virus-encoded small RNA in-situ hybridization (EBER-ISH) in gastric tissue samples on formalin-fixed, paraffin-embedded. Finally, the immunoscore and the Combined Positive Score were calculated.
Results. ITGA samples were 21.8% ± 13.6% and 14.8% ± 14.8% CD3 + and CD8 + positive respectively, 100% had low PD-1 expression, CPS score for PDL-1, 91.7% had <1 and 8.3% had >1. In EBER-ISH, 20.8% were positive, and in immunoscore, 16.7% had a score > 25%.
Conclusion. This paper reports advanced ITGA cases with an atypical tumor microenvironment, compared to previously reported data. It is important to consider that the tumor microenvironment in gastric cancer is heterogeneous, which makes the analysis of microsatellite instability in this type of sample relevant.