ARG1 and neoplasm: In return, microglia secrete tumor proliferation promoting factors including epidermal growth factor (EGF) (Coniglio et al., 2012) and vascular endothelial growth factor (VEGF), TGF-β, arginase-1 (ARG1), and IL-10 (Gabrusiewicz et al., 2011; Li and Graeber, 2012).