In particular, the activating receptor, NKG2D, recognizes various ligands (e.g., MHC class I polypeptide-related sequence A (MICA), MHC class I polypeptide-related sequence B (MICB) and UL16 binding proteins (ULBPs) 1–6) on cancer cells and is critical for tumor lytic abilities of NK cells. This evidence concerns the gene KLRK1 and cancer.