KLRK1 and neoplasm: Among activating receptors, Natural-Killer receptor group 2, member D (NKG2D), Natural cytotoxicity receptors (NCRs) and DNAX-associated molecule-1 (DNAM-1 or CD226) are mainly involved in tumor immune surveillance, since they bind self-proteins that are normally absent or poorly expressed on healthy cells and up-regulated upon tumor transformation.