Our hypothesis states that the three EGFR mutations commonly seen in lung cancer (L858R and the 15 bp and 18 bp deletions), which comprise >80% of all EGFR mutations seen in lung cancer, occur due to selection of cells with these mutations during lung development, resulting in greatly increased frequencies of these mutations compared to similar types of non-selected mutations in EGFR and other genes. The gene discussed is EGFR; the disease is lung cancer.