IDO1 and hepatocellular carcinoma: The results are shown in Figure 8, and the TIMER analysis showed that STAT1 was significantly positively correlated with PD1 (r = 0.448); PD-L1 (r = 0.444); CTLA-4 (r = 0.436); FGFR2 (r = 0.354); FGFR3 (r = 0.36); and IDO1 (r = 0.387) in HCC, and these checkpoints were regulated by purity.