To investigate whether the suggested decreased efficiency of cetuximab binding to the R521K mutant extracellular domain of EGFR in PE/CA-PJ15 cells results in a less effective inhibition of EGFR phosphorylation, we monitored the level of phospho-EGFR and phospho-ERK in HNSCC cells by immunoblots. The gene discussed is EGFR; the disease is head and neck squamous cell carcinoma.