IDO1 and cancer: Indeed, in NSCLC, the activation of HIF-1α and EGFR, which has been shown to induce a CSC (cancer stem cell) phenotype, and the activation of the RAS-RAF-MEK-ERK or lipoyltranferase 1174 signaling pathway, along with the presence of markers for tumor regeneration such as high Ki-67 expression and the overexpression and enhanced activity of indoleamine 2,3-dioxygenase (IDO), are all associated with radioresistance.175