EGFR and lung cancer: As a result, several important genes in lung cancer have been identified, such as EGFR, ALK and ROS1. EGFR tyrosine kinase inhibitors (TKIs) erlotinib and gefitinib were the first class of molecularly targeted agents approved by the U.S, Food and Drug Administration (FDA) in 2004, up to today, erlotinib, gefitinib and other EGFR TKIs such as afatinib and osimertinib are all used for the treatment of metastatic NSCLC patients whose tumors have EGFR exon 19 deletions or exon 21 L858R mutations [16–20].