Previous studies showed that the serum level of soluble MICA (sMICA) is an independent prognostic factor for advanced hepatocellular carcinoma [22], and the interaction of NKG2D and corresponding ligands MICA/B may play an important role in immune-surveillance against cholangiocarcinoma and hepatocellular carcinoma [23,24]. Here, KLRK1 is linked to cholangiocarcinoma.