MDSCs contribute to tumor progression through different mechanisms, including the induction of angiogenesis and EMT, the secretion of matrix metallopeptidase 9 (MMP9), VEGF (in STAT3-dependent manner), transforming growth factor (TGF)-β, and growth factors (i.e., EGF), and the promotion of pre-metastatic niches and immune evasion (Figure 3) [62,74]. Here, STAT3 is linked to neoplasm.