MMP9 and neoplasm: MMP-9 is one of the most important MMPs involved in tumor invasion and metastasis (Si et al. 2018), whereas MMP-1 has also been reported to activate endothelial PAR-1 to facilitate endothelial permeability and transendothelial migration of tumor cells, and thus to promote metastatic dissemination (Andrae et al. 2008).