MMP9 and neoplasm: Because recent evidence suggests that MT1-MMP (but not MMP-2 or MMP-9) express proteolytic activity that mediates fibroblast migration through type I collagen [14] and MMP-2 and MMP-9 deficient mice develop normally, it is possible that MMP-2 or MMP-9 play a role in more complex models of tumor invasion or growth because they disrupt tumor-stromal signaling rather than matrix degradation.