Methods: mRNA expression of genes encoding enzymes involved in the ISGylation process (EFP, HERC5, UBA1, UBC and USP18) was evaluated by quantitative real-time PCR in 38 pairs of tumour and adjacent non-tumour tissues from patients with hepatocellular carcinoma and correlated with distinct clinical laboratory parameters. This evidence concerns the gene USP18 and hepatocellular carcinoma.