MMP9 and lung cancer: We previously showed that cigarette smoke extract (CSE) and cigarette smoke (CS) induced oxidative stress, inflammation, EMT and fibrosis in a lung cancer cell culture and in the lungs of mice through the activation of SH2 domain-containing phosphatase (Shp) 2 and Rac1 signaling pathways, respectively, which further activate MMP-9 production [11–13].