IDO1 and neoplasm: The adult neural tube cell tumors represent low tumor mutational burden (TMB) tumors that upregulated IDO1 expression in an inflammatory environment and enhanced IDO1 expression shaped a suppressive microenvironment by suppressing T-cell activity, which is one of the mechanisms of immune evasion in adult neural tube cell tumors (Folgiero et al., 2016; Munn and Mellor, 2016).