PDCD1 and hepatocellular carcinoma: PD-1 was shown to be highly expressed in tumour-infiltrating lymphocytes (TIL) of the liver tissues in HBV-related HCC [22, 26] and the expression levels correlated with portal vein tumor thrombosis [22], indicating the potential of PD-1 expression in TIL of liver tissues to serve as a prognostic marker of HBV-related HCC.