Upregulated expression of MMP9 in tumor samples and serum of cancer patients was discovered to positively correlate with tumor stage and poor clinical outcome in a large variety of malignancies, including ovarian, colorectal, breast, and non-small cell lung cancer, suggesting that MMP9 could even be considered a potential prognostic marker for cancer patients [5,135,136,137,138]. Here, MMP9 is linked to cancer.