EGFR and head and neck squamous cell carcinoma: A systematic review of a 113-patient HNSCC cohort found that the L858R substitution, associated with sensitivity to EGFR TKIs in NSCLC, was found in only 2.5% of the patients; the T790M substitution in exon 20, was found in 7.5% of patients; and in-frame deletions in exon 19, making up 45% of all EGFR mutations in NSCLC and linked to responsiveness to EGFR TKIs, were observed in 22% of all EGFR-mutated HNSCCs (37).