CXCR4 and neoplasm: In concert with the regulation of these intracellular proteolytic systems, extracellular matrix metalloproteases such as MMP-1, MMP-7 and MMP-9 have been reported to play a pivotal role in human tumor systems and autoimmune disorders to provide and actively change an appropriate microenvironment for the tumor cells as well as relay intracellular signals by involving cytokine receptors such as CXCR4 [27-29].