Considering not only IDO1 but also IDO2 and TDO2 could catalyse the first and rate‐limiting step of tryptophan (Trp) catabolism, we analysed both of their expression status with GEPIA, a web‐based tool to deliver fast and customizable functionalities based on the cancer genome atlas (TCGA) and genotype‐tissue expression (GTEx) data. Here, IDO1 is linked to cancer.