EGFR and chronic obstructive pulmonary disease: At the same time, altered expression of its ligands by extracellular stimuli and injury, such as cigarette smoking and consequent oxidative stress, can lead to upregulation of EGFR and activation of its signaling pathways, causing structural and functional alterations in the lung epithelium and impairment of cell phenotype, that contribute to different forms of chronic obstructive pulmonary disease (COPD).