ERBB4 and head and neck squamous cell carcinoma: No significant differences in the percentages of EGFR‐, HER2‐, HER3‐, and HER4‐positive cells (P ≥ 0.143) and the ΔMFI of receptor‐positive cells (P ≥ 0.170) were observed between cetuximab‐sensitive, intrinsically cetuximab‐resistant, and acquired cetuximab‐resistant HNSCC cell lines.