Exosomes were also drivers for tumor cells metastatic spread, circ_MMP2 was found to be driven by high metastatic tumor cells-secreted exosomes into normal hepatocellular cells and promoted tumorigenesis and metastasis in hepatocellular cancer via sponging miR-136-5p to enhance parental gene MMP2 (matrix metalloproteinases 2) expression (26, 64). Here, MMP2 is linked to hepatocellular carcinoma.