Thus, while the AhR is activated in hepatocellular carcinoma [156] and reported to enhance tumour growth, migration and metastasis [157] possibly acting via IDO induction [34], and is associated with malignant progression and poor survival of patients with brain tumours [24], others [158] reported that AhR activation by kynurenine impairs progression and metastasis of neuroblastoma. Here, IDO1 is linked to neoplasm.