MMP9 and hepatocellular carcinoma: Based on the current findings, however, CK-19, which is expressed in the cytoplasm and cytomembrane of HCC cells, may be directly secreted into the extracellular matrix, where is hypothetically involved in initiation of a signaling cascade involving cytomembrane integrin, thereby inducing various matrix-degrading enzymes such as MMP-9 [20, 21].