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. Here, IDO2 is linked to cancer.