MMP9 and neoplasm: CAFs could secrete a large number of growth factors, cytokines and chemokines and mediate related signalling pathways such as TGF-β/TGF-β receptor, VEGF/VEGF receptor and SDF-1 (CXC12)/CXC chemokine receptor type 4, or synthesize related proteins such as podoplanin, FAP and Winglesstype MMTV integration site family member 2 (47), or secret MMP-9/13 to promote tumour angiogenesis (48–51).