TPS9151 Background: Although chronic obstructive pulmonary disease (COPD) and lung cancer share a common risk factor, namely smoking, health care providers usually overlook the symptom of COPD in the management of lung cancer. Should, then, lung cancer patients undergo pulmonary function tests (PFT) to identify the presence of COPD? Our study was performed to describe the results of pulmonary function tests and define risk factors for COPD in non-small cell lung cancer (NSCLC) patients. Methods: A total of 31 eligible patients with NSCLC but no obvious symptoms of COPD participated. We collected baseline characteristics and conducted a detailed assessment of pulmonary function, particularly spirometry, lung volume measurement, and diffusing capacity of carbon monoxide (DLCO). Dyspnea was assessed using modified Borg (mBorg) and modified Medical Research Council (mMRC) scores. Results: Twelve patients had airflow limitation (FEV1/FVC<0.7). These patients had mean percent predicted FEV1, RV and DLCO of 52%, 143% and 66% respectively, and a mean RV/TLC of 0.55. Being male, and having a smoking history, low body mass index and squamous cell carcinoma were significantly associated with obstruction in univariate analysis. However, obstruction was not more common in advanced stage than in locally advanced NSCLC. Neither mBorg nor mMRC differed between obstructive and non-obstructive groups. Discussion: COPD was found in patients with NSCLC who had never been diagnosed as, or showed symptoms of, COPD. Male, smoking history, low BMI and squamous cell carcinoma were significantly associated with obstruction.