Relationship of tumour stroma ratio andmicroenvironment with PDL-1 expression andprognostic parameters in gastric adenocarcinomas

Tumor-stroma ratio is an important component of microenvironment assessment. In our study, perineural invasion, deep invasion and increased lymph node metastasis according to Tumor-Node-Metastasis staging, and high clinical stage were observed in the high tumor stroma ratio group in accordance with the literature. High stroma ratio was observed in tumors with widespread infiltration in the stomach. Histologically, high stroma rates were found in poorly cohesive and mixed types. Progression-free survival and overall survival were low in the group with high stroma rates. Cluster of differantiation 8 (+) T lymphocytes are important in antitumor immunity. Tumoral cells are recognized by cluster of differantiation 8 (+) T lymphocytes and eliminated by their cytotoxic activity. Therefore, the amount of cluster of differantiation 8 (+) lymphocytes is an indicator of tumor regression. In our study, although not statistically significant, higher progression-free and median survival was observed in the group with higher cluster of differantiation 8 (+) lymphocytes. The group with high cluster of differantiation 8 (+) T lymphocyte ratio is associated with increased Programmed Cell Death Ligand-1 expression and low stroma ratio. Immune checkpoints are immune regulators. Blockade of the Programmed Death Protein-1 / Programmed Cell Death Ligand-1 pathway activates the antitumor function of the immune system. This is the most commonly used immunotherapy. Programmed Cell Death Ligand-1 expression identifies patients who will benefit from this therapy. In our study, 3 different combined positive score thresholds were used. For all of them, combined positive score positivity was positively correlated with cluster of differantiation 8 (+) T lymphocyte density and negatively correlated with tumour stroma ratio. Although not statistically significant, Programmed Cell Death Ligand-1 expression can be mentioned as associated with better survival in combined positive score group with threshold value 1. Our study provides a comprehensive perspective on the concept of tumor microenvironment in gastric adenocarcinomas, and its results reveal the importance of the tumor microenvironment. Further studies on this topic are still needed. Key words: Programmed Cell Death Ligand-1, CD8, Tumour Stroma Ratio, Tumour Microenvironment