TDO2 catalyses the first step of tryptophan (Trp) catabolism along the kynurenine pathway (KP) and is known to play an important role in GBM as it promotes tumor cell motility and suppresses anti-tumor immune responses via production of Trp metabolities that activate the aryl hydrocarbon receptor (AHR) (24). This evidence concerns the gene AHR and neoplasm.