ERBB3 and head and neck squamous cell carcinoma: Factors thought to contribute to cetuximab resistance in SCCHN patients include upregulation of ligands for EGFR and human epidermal growth factor receptor 3 (HER3) (7, 8), heterodimerization of EGFR and HER2 with HER3 (9), overexpression of HER2 and HER3 (10), and overexpression and aberrant nuclear localization of EGFR (11).