Moreover, many other targets have been considered as prognostic indicators for HCC, including immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) (49), epithelial neutrophil-activating peptide-78 (CXCL5) (50), CXCR6 (51), and so on. This evidence concerns the gene IDO1 and hepatocellular carcinoma.