Furthermore, by secreting VEGF, Bv8, MMP-9, and basic fibroblast growth factor (b-FGF), MDSCs play an important role in TME reorganization, cancer angiogenesis, metastasis, and the formation of pre-metastatic niches, hence regulating cancer initiation and progression (Fig. 9) [219, 221]. This evidence concerns the gene MMP9 and cancer.