MMP9 and breast cancer: Mainly, MMP-2 and MMP-9 are most well-studied in cancer cells since these MMPs are highly secreted in breast cancer cells as a proenzyme before activation through hydrolysis and degrade collagen type-IV basement membrane (BM), which in turns alters the ability of BM to disrupt cancer cell mobility (Li et al., 2017; Zhang et al., 2014).