Tryptophan through its degradation by indoleamine-2,3-dioxygenase 1 (IDO1) and tryptophan-2,3-dioxygenase 2 (TDO2) to kynurenine has emerged as an important metabolic regulator of tumor progression, immune suppression and immune tolerance in the tumor microenvironment. This evidence concerns the gene TDO2 and neoplasm.