IDO1 and breast carcinoma: Doxorubicin was found to increase the level of indoleamine 2,3-dioxygenase (IDO), an enzyme that converts tryptophan to kynurenines and is involved in the suppression of the immune response of breast cancer cells in murine models, but in combination with a small molecule of an IDO inhibitor (NLG919) it enhanced ICD, inducing a synergistic therapeutic effect via the reversal of CD8+ T cell suppression [95].