EGFR and head and neck squamous cell carcinoma: Moreover, several signaling pathways and key pathway components are known to be disrupted in HNSCC, such as epidermal growth factor receptor (EGFR) signaling, phosphatidylinositol-3-kinase/protein kinase B (PI3-K/Akt) signal transduction pathway, mammalian target of rapamycin (mTOR), nuclear factor–kB (NF-kB) transcription factors and heat shock protein 90 (Hsp90, 18].