IDO1 and nasopharyngeal carcinoma: These results are consistent with and extend the findings of previous studies that reported IDO-1 over-expression in EBV+ nasopharyngeal cancer (Liu et al., 2014), HPV+ cervical (Kobayashi et al., 2008) and head-neck squamous cell cancer (Sailer et al., 2019), and chronic HCV infected liver (Larrea et al., 2007).