MDSCs promote tumor progression by enhancing angiogenesis and metastasis via STAT3-driven VEGF upregulation, MMP-9 expression (57, 172, 173), and epithelial-mesenchymal transition (EMT) with TGF-β, IL-6, and IL1-β (172, 173) and prepare pre-metastatic niches in through mechanisms involving exosomes, TGF-β, S100A8/A9, and VEGF (58, 169, 172, 173). The gene discussed is MMP9; the disease is neoplasm.