MMP9 and neoplasm: When either CRC or CSC presents the CD51 marker and is co-localized with the TGFβ receptor, they can promote TGFβ/Smad signaling that upregulates epithelial–mesenchymal transition (EMT)-related genes, such as PAI1, MMP9, and Snail, which then promotes sphere formation, cell motility, and subsequent tumor formation (22, 23).