MMP9 and neoplasm: Furthermore, the expression levels of proliferating cell nuclear antigen (PCNA), matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and IL-6 were significantly elevated in the tumor tissues of the RFA-treated group compared to the control group (Ke et al., 2010).