IDO2 and cancer: The overview derived from the TCGA dataset shows a wide range of IDO2 expression among different cancer types [37], including non-small cell lung cancer (NSCLC) [40], glioma [41], colon, gastric, and renal tumors [9,32], and medullary thyroid carcinoma [42], with the highest median expression in diffuse large B-cell lymphoma and the lowest median expression in acute myeloid leukemia [43].