DPP4 and hepatocellular carcinoma: Having shown that DPP9, DPP8, DPP4 and FAP were overexpressed in liver tumors (Figure 2A–D), and that high co-expression of the DPP4 gene family members was significantly associated with shorter survival times in HCC (Figure 4B), we next assessed the gene expression signature correlated with the DPP4 gene family in HCC patients to gain mechanistic insights.