This involves (1) up-regulating TDO2, IDO1 and IDO2 in this order of preference; (2) expressing two Trp transporters to provide and ensure continued availability of the substrate of the above enzymes; (3) expressing the next enzyme FAMID to ensure that Kyn production is not hampered; (4) by expressing KAT1, tumours appear to favour the production of KA and while KA possesses both anti- and pro-inflammatory properties, it is likely that tumours intend to take advantage of these latter properties. The gene discussed is IDO1; the disease is neoplasm.