KLRK1 and neoplasm: The NK group 2, member D (NKG2D) serves as an activating immune receptor expressed on the surface of a vast majority of NK cells, CD8+ T cells, γδ T cells, and in certain subsets of CD4+ T cells [8], NKG2D could trigger cytotoxic activity of immune effector lymphocytes after binding to its distinct ligands, which consist of the MHC class I-related chain (MIC) family (MICA and MICB) and the UL16 binding protein or retinoic acid early transcript (ULBP/RAET) family (ULBP1-6) expressed on the surface of tumor cells.