EGFR and head and neck squamous cell carcinoma: EGFR-targeted recombinant immunotoxin hDT806 exhibits significant antitumor activities in HNSCC, causing the direct disruption of EGFR signaling; hDT806 further induces transcription inhibition, DNA damage, as well as apoptotic responses, which, in turn, may contribute to the antitumor efficacy of hDT806 distinct from erlotinib or cetuximab.