The indoleamine dioxygenase-kynurenine -aryl hydrocarbon receptor (IDO–Kyn–AhR) axis was also identified as a driving signaling pathway in thyroid tumorigenesis, mediating an immunosuppressive microenvironment that promoted the acquisition of the mesenchymal phenotype, leading to enhanced tumor invasiveness and metastasis [24]. The gene discussed is IDO1; the disease is neoplasm.