MMP9 and head and neck squamous cell carcinoma: Samara et al. [33] found that the binding of CXCR4 to CXCL12 lead to an increase in head and neck squamous cell carcinoma (HNSCC) cell adhesion and MMP-9 secretion, suggesting that CXCR4 may be a novel regulator of metastatic processes in HNSCC.