IDO1 and liver cancer: In this study, we found that EBV+ gastric cancer, HPV+ cervical and head-neck squamous cell cancer, and HCV+ liver cancer (but not HBV+ liver cancer) showed over-expression of IDO-1 (Figure 4A), but only EBV+ gastric cancer and HPV+ head and neck squamous cell cancer showed over-expression of IDO-2 (Figure 4B).