MMP2 and neoplasm: Studies have shown that CAFs exist at the PNI site and the produced inactive matrix metalloproteinase-2(MMP-2) is activated by membrane-type 1 matrix metalloproteinase (MT1-MMP) produced by tumor cells, which degrades extracellular collagen in the perineural niche and promotes the spread of cancer cells in the perineural space [68,75].