MMP9 and neoplasm: Proprotein convertase subtilisin/kexin 9 (PCSK9) mediates epithelial-mesenchymal transition (EMT) in colon tumor cells by upregulating snail homolog 1 (Snail 1), downregulating E-cadherin expression, and simultaneously upregulating N-cadherin and matrix metallopeptidase 9 (MMP9) expression, thereby promoting tumor metastasis (86).