IDO1 and neoplasm: - Competing glucose substrate utilization by rapidly expanding carcinoma cells.- Lactate synthesis and tumor reliance on anaerobic glycolytic pathway: Associated suppression by M2 macrophages; Upregulation in tumor PD-L1 production and CD8+ T cell apoptosis- Depletion of critical amino acids such as tryptophan (IDO overproduction) and glutamine.