Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) play pivotal roles in cancer viability and motility, and they facilitate tumor cells escaping the host immune system by catalyzing the initial step of the Kyn production. The gene discussed is TDO2; the disease is neoplasm.