MMP9 and cancer: Zhou et al. demonstrated that cancer-derived exosomal miR-21 could convert hepatic stellate cells (HSCs) to CAFs by downregulating PTEN, thereby activating CAFs and promoting cancer angiogenesis by upregulating the expression of VEGF-α, MMP2, MMP9, bFGF, and transforming growth factor-β (TGF-β).