HIF1A and neoplasm: Together with these soluble factors, tumor hypoxia, via HIF-1α stabilization and the production of downstream effectors, plays a role in facilitating MDSC mobilization into the circulation and recruitment to tumors (Du et al., 2008; Erler et al., 2009; Wong et al., 2011; Sceneay et al., 2012; Chafe et al., 2015; Figure 2), and regulates the immunosuppressive functions of MDSC (Corzo et al., 2010).