EGFR (HER1, ErbB1) is an RTK expressed on the surface of cells of mesodermal and ectodermal origin, and it mediates cell growth, proliferation, and differentiation in numerous organs [16, 17]. EGFR belongs to the ErbB family of RTKs,
which also includes HER2 (ErbB2), HER3 (ErbB3), and HER4 (ErbB4). EGFR
binds at least seven highly variable growth factor ligands [18]. Upon stimulation,
EGFR undergoes combinatorial homo- or hetero-dimerization with one of the proteins of the HER family, thereby activating an expansive signaling network [16, 19,
20]. The EGFR transmembrane protein has a large extracellular component (with 4
domains, ~620 amino acids) that primarily serves as ligand-binding sites and which
is anchored by a short helical transmembrane domain to the intracellular tyrosine
kinase domain (TKD) (Fig.?1) [18].
EGFR is believed to play a role in the pathogenesis of lung cancer and is overexpressed in a majority of NSCLCs [21, 22]. However, the clinical importance of
EGFR expression in the general NSCLC population is unclear. There was some
suggestion that EGFR expression may serve as a predictive biomarker [21], but this
has been superseded by mutational analysis after the identification of actionable
driver mutations in the EGFR gene.
