C6 and hepatocellular carcinoma: According to the result from Gepia database (Figure 2), the mRNA expressions of C1R, C6, C7, C8A, C9, CFP, CFHR3, and MBL2 were still significantly lower in HCC samples (n = 368) than in normal samples (n = 160), while the mRNA expression of C1QA was significantly higher in HCC samples (n = 368) than in normal samples (n = 160).