IDO1 and cancer: For example, Epacadostat tends to show the best inhibition against cancer cells with constitutive expression of IDO1 (i.e., the cancer cells produce IDO1 even when they are not inflamed) rather than those with inducible activity (i.e., the cancer cells produce IDO1 in response to T-cell infiltration); the concentration of Epacadostat administered may be insufficient for blocking the IDO1/AhR pathway; as mentioned earlier, there are multiple sources of IDO activation at different stages; IDO1 expression varies among different cancer cell lines.