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EGFR is a 170 kDa transmembrane receptor that induces tyrosine kinase activity affecting cell growth. EGFR mutations can occur in various parts of the gene. In NSCLC, the mutations occur almost exclusively in the exons encoding the kinase domain （exons 18 to 21）. They most commonly include the in-frame deletion of exon 19 （del19） and L858R mutation in exon 21.Del19 constitutes 44–51%, and exon 21 L858R mutation constitutes 38–40%.