MMP2 and hepatocellular carcinoma: The metastasis of HCC involves in elevating expression of metastasis‐related molecules, including keratin 19 (K19) 9, epithelial cell adhesion molecules (EpCAM) 10, matrix metalloproteinase 2/9 (MMP2/9) 11 and CXCR4 12 in hepatoma cells.