Beyond secretion of growth factors for cancer stem cells and proteases, which increase the laxity of the extracellular matrix and promote metastatic spread, M2 macrophages also release mediators such as IL-10, TGFβ, prostaglandins, and indoleamine 2,3-dioxygenase, which promote the expansion of regulatory T cells and metabolically starve effector T-cells. This evidence concerns the gene IDO2 and cancer.