ERBB4 and head and neck squamous cell carcinoma: EGFR, which is highly expressed in a significant majority (up to 80–100%) of HNSCC, is of the prototype receptor of the HER tyrosine kinase receptor family, which includes HER1/ErbB-1/EGFR, HER2/neu/ErbB-2, HER3/ErbB-3 and HER4/ErbB-4 [6].