Glucocorticoids may also modulate the patterned immune response via the glucocorticoid induced tumor necrosis factor receptor (GITR) [64], which also induces IDO [65], being another route whereby CAR and HPA axis activation can suppress tryptophan and the tryptophan-melatonin pathway, whilst increasing kynurenine-driven AhR activation to heighten the NAS/melatonin ratio, to modulate cancers and their interactions with immune cells in the tumor microenvironment. The gene discussed is IDO1; the disease is neoplasm.