Immunohistochemical Expression of Programmed Death Ligand-1 (PD-L1) in Gastric Adenocarcinoma and Non-Neoplastic Gastric Epithelium

Background: Tumor progression is heavily influenced by immune evasion strategies such as the expression of Programmed Death Ligand-1 (PD-L1), which also presents as a promising target for cancer therapies. This study aimed to investigate the immunohistochemical presence of PD-L1 in gastric adenocarcinoma tissues and to compare it with non-cancerous gastric mucosa, and explore its relationship with various clinicopathological factors. Methods: This comparative analytical cross-sectional study was conducted at the Histopathology Division, Department of Pathology, Peshawar Medical College, Riphah International University, Islamabad, over one year (March 2022–February 2023). A total of 60 formalin-fixed, paraffin-embedded (FFPE) samples were analyzed, comprising 30 gastric adenocarcinoma specimens from gastrectomies and 30 non-neoplastic gastric mucosa samples from endoscopic biopsies. Samples were selected using non-probability consecutive sampling. PD-L1 expression was assessed by standardized immunohistochemistry, scored for intensity and proportion of positive cells, and reviewed independently by two pathologists. Statistical analysis was performed using SPSS version 20.0; Chi-square and Fisher’s exact tests were applied, with p < 0.05 considered significant. Although a smaller comparison group (e.g., 2:1 ratio) could suffice to demonstrate absence of PD-L1 in non-neoplastic tissue, an equal ratio (1:1) was chosen to strengthen comparability and analysis. Results: PD-L1 expression was detected more frequently in 14 out of 30 neoplastic gastric tissues (46.6%) compared to 2 out of 30 non-neoplastic samples (6.6%), although this difference was not statistically significant (p=0.171). No significant associations were found between PD-L1 expression and patient age, sex, tumor location, histological subtype, tumor grade, stage, lymph node involvement, or presence of perineural or vascular invasion. Conclusion: PD-L1 is commonly expressed in gastric adenocarcinoma; however, its expression does not appear to be significantly linked to major clinicopathological characteristics. Multicenter studies with larger study population are warranted to better understand the prognostic value and therapeutic potential of PD-L1 in gastric cancer.