Previous clinical studies have also shown that high levels of NKG2D ligands were not associated with the extent of NK cell infiltration into the tumors or better prognosis for patients with breast, lung, or ovarian cancers [41], suggesting that expressions of NK cell-activating ligands likely vary significantly between cancer types and tumor context, thus hindering their stand-alone prognostic potential. This evidence concerns the gene KLRK1 and ovarian carcinoma.