NK cells express a variety of activating receptors, including the NK group 2 member D (NKG2D), the DNAX accessory molecule-1 (DNAM-1), and the natural cytotoxicity receptors (NCRs: NKp30, NKp44, and NKp46), that provide activating signals upon binding to stress-induced ligands that are expressed in tumor, but not in normal cells. This evidence concerns the gene KLRK1 and neoplasm.