MMP9 and metastatic malignant neoplasm in the lymph nodes: Among MMPs, MMP-2 and MMP-9 are collagenase that can selectively degrade type IV collagen, a major component of ECM; overexpression of MMP-2 or MMP-9 is associated with more lymph node metastases, distant metastases and poor survival in head and neck SCC (21–24).