Since it is unknown whether high IDO-1 expression is a sufficient predictor of response to IDO-1 inhibitors or whether high expression of other genes in the IDO pathway (IDO-2 and TDO-2) is also necessary for response to IDO-1 inhibitors, in this study, we looked for the genomic and immunologic correlates of IDO pathway expression in cancer using the Cancer Genome Atlas (TCGA) dataset. This evidence concerns the gene TDO2 and cancer.