Differential infiltration of CD4+ and CD8+ T cells and expression of PD-L1 in paired biopsy and resection specimens of gastric and colorectal adenocarcinomas.

Objective: To compare CD4+ T cell, CD8+ T cell infiltration and PD-L1 expression between paired biopsy and resection specimens in gastric and colorectal adenocarcinoma, and evaluate their clinical significance. Methods: Paired biopsy and resection specimens from 38 gastric and 40 colorectal adenocarcinoma patients were assessed by immunohistochemistry for CD4+ T cell, CD8+ T cell density and PD-L1 expression. Correlations with clinicopathological parameters and tumor markers were analyzed. Results: In gastric adenocarcinoma, resection specimens showed significantly higher CD4+ T cell, CD8+ T cell density and PD-L1 expression than biopsies (all P<0.05), with CD4+ T cells positively correlated with CA19-9 (R = 0.523, P = 0.026). In colorectal adenocarcinoma, CD8+ T cell density was higher in resection specimens (P = 0.0353); CD4+ T cells negatively correlated with Ki-67 (R=-0.370, P = 0.019), and CD4+/CD8+ ratio negatively correlated with mismatch repair protein expression (R=-0.342, P = 0.029). In both cancers, CD4+/CD8+ ratios at tumor center and invasive margin were positively correlated (gastric: R = 0.5683, P = 0.0002; colorectal: R = 0.7324, P<0.0001). Preoperative neutrophil-to-lymphocyte ratio positively correlated with tumor diameter in both cancers (gastric: R = 0.449, P = 0.011; colorectal: R = 0.631, P = 0.001). CD4+ T cell density differed significantly between cancer types (P <0.0001). ROC analysis demonstrated limited predictive value of biopsy specimens for surgical findings, particularly in colorectal cancer (AUC 0.5-0.7). Conclusion: Biopsy specimens inadequately represent the immune microenvironment of resection specimens, especially in gastric adenocarcinoma. Tumor-type-specific immune assessment of biopsies is essential for guiding precise immunotherapy decisions.