CD8A and neoplasm: In recent years, tumor immune microenvironment has been critical in the occurrence and development of gastrointestinal tumors, tumor infiltration by T lymphocytes, including helper T cells (CD4+), cytotoxic T cells (CD8+), and T regulatory cells (Tregs, FOXp3+), is known to predict prognosis in multiple cancers including breast cancer, colorectal cancer, head and neck carcinoma, lung cancer, and esophageal cancer [12–20].