EGFR (epidermal growth factor receptor) is a transmembrane tyrosine kinase receptor that, upon ligand binding, triggers two main signaling pathways. These include the RAS-RAF-MAPK axis, which is mainly involved in cell proliferation, and the PI3K-PTEN-AKT pathway, which is mainly involved in cell survival and motility. Mutations in KRAS, BRAF, or PIK3CA result in continuous activation of the downstream RAS-MAPK or PI3K pathways, regardless of whether EGFR is activated. EGFR missense and deletion mutations have been found in 13.4% of non-small cell lung cancer patients, within exons 18 through 21 of the kinase domain. EGFR is expressed by many epithelial tumor cells, including biliary and pancreatic cancers. EGFR mutations predict response to EGFR inhibitors in lung cancer.