MET and head and neck squamous cell carcinoma: It has been shown in vitro and in tumor specimens that the expression of the ligand hepatocyte growth factor (HGF) scatter factor and its receptor HGFR (MET) increase during invasive growth of SCCHN and this pathway, by constitutively co-activating other important pathways, may play a critical role in the metastatic process of SCCHN cells [25].