Lung cancer has remained as the top cancer killer in Hong Kong. Even for early resectable stage of lung cancer, only around 60-70% of patients can survive for 5 years after operation, mostly related to disease recurrence. Therefore there is urgent need for predictive biomarkers that can potentially help in monitoring patients for risk of disease recurrence after operation. Recent studies have suggested an important role of oxidative stress in the development of lung cancer and our preliminary data have suggested that some of the oxidative stress markers in blood could be predictive of response to systemic chemotherapy for lung cancer. Apart from potential biomarkers from blood, ongoing study has also been conducted to investigate the predictive role of biomarkers in exhaled breath condensate in lung cancer patients undergoing chemotherapy. Exhaled breath condensate can be collected simply with a disposable commercially available device that allows trapping of breath condensate via a cooling column during normal breathing for 20 minutes. Therefore this study aims at investigating the role of blood and exhaled breath condensate oxidative stress biomarkers before and after surgical lung resection for lung cancer in predicting subsequent clinical outcome, i.e., timing of disease recurrence. Recruited subjects will undergo interval sampling of blood and exhaled breath condensate, without any additional invasive interventions. The study subjects will be followed up for 5 years for subsequent disease recurrence.