MMP2 and osteosarcoma: Expression of MMP-2 and MMP-9 is highly negatively correlated with the occurrence and development of tumors (Song et al., 2016), and invasive osteosarcoma cell lines secrete large amounts of these proteins (Liu B. et al., 2016) also reported that MMP-2 and MMP-9 expression was significantly increased in tumor tissues of breast cancer patients.