Subjects

Three groups of subjects comprising 10 non-smokers without COPD (non-smokers group), 9 smokers without COPD (smokers group), and 9 smokers with COPD (COPD group), respectively, were recruited from Qilu Hospital (Cheeloo College of Medicine, Shandong University), where all subjects underwent therapeutic lung resection for the removal of tumors. Noncancerous lung tissue blocks 15–25 mm in size located at least 5 cm from the tumor margin were collected from resected specimens, fixed in 10% formaldehyde, and embedded in paraffin. According to the guidelines of the Global Initiative of Chronic Obstructive Lung Disease (GOLD), all subjects underwent spirometry and those with a ratio of forced expiratory volume in one second over forced vital capacity (FEV₁/FVC) of less than 70% were diagnosed as having COPD. Patients were excluded from this study if they had respiratory infections, bronchial asthma, bronchiectasis, congestive heart failure, or neuromuscular disorders. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Ethics Committee of Qianfoshan Hospital of Shandong University (approval number 2019S044). Informed consent was obtained from all subjects.