Downregulation in gene expression of the NKG2D ligands, ULBP-1, ULBP-3 and MICA/B has been shown in cisplatin-resistant lung cancer cell lines compared to their parental counterparts, with mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MAPK/Erk) signalling implicated in this reduced ligand expression [18]. This evidence concerns the gene KLRK1 and lung cancer.