CD226 and neoplasm: In addition, reduced CD226 expression on peripheral NK cells or tumor-infiltrating lymphocytes is correlated with tumor progression, resistance to immunotherapy, and poor prognosis in gastric cancer, hepatocellular carcinoma, acute myeloid leukemia, pancreatic cancer, melanoma, neuroblastoma, and chronic lymphocytic leukemia [44,45,46,47,48,49,50,51].