CD8A and cancer: The digestive tract tumor microenvironment encompasses highly complex cellular populations, such as cytotoxic T lymphocytes (CD8+ T cells) with immune surveillance functions, B cells involved in antigen presentation, TAMs with highly plastic phenotypes, and cancer-associated fibroblasts (CAFs) that regulate invasion and metastasis through the secretion of extracellular matrix (ECM) components (97, 98).