STAT3 and neoplasm: The two groups of signaling previously described to be responsible for accumulation and differentiation of MDSCs include tumor—derived growth factors (STAT3, IRF8, C/EBPβ, Notch, adenosine receptors A2b signaling, NLRP3, Rb1) and proinflammatory cytokines produced by tumor stroma (NF-κβ pathway, STAT1, STAT6, PGE2, COX2) [7].