AHR expression is increased in aggressive malignancies and constitutively localises to the nucleus, suggesting that it is chronically activated to facilitate tumour progression.195,196 Moreover, AHR antagonism diminished cell viability in patient-derived glioma and meningioma cells following in vitro drug treatments,195 unlike inhibition of Trp-degrading enzymes. This evidence concerns the gene AHR and central nervous system cancer.