Lung cancer is one of the leading causes of cancer-related death in Taiwan. Early diagnosis of lung cancer may improve cancer survival. Low-dose computed tomography (LDCT) was thought to be the best screening tool for lung cancer. However, there is growing concerns about radiation exposure, high cost, and high rate of false-positive screening result. Epidemiologic studies from western countries showed that cigarette smoking is the major cause of lung cancer, and other risk factors may include age, environmental pollution, occupational exposures (included of radon exposure), gender, race, and pre-existing lung diseases. Adenocarcinoma is the major type of lung cancer in Taiwan and is less attributable to smoking. The investigators need a different risk prediction model adapted to the investigators country.