There are four main reasons for the difficulty of early diagnosis of lung cancer as follows: 1. Early stage of lung cancer is often asymptomatic, especially for tumors growing in the periphery of the lung. About 1/3 of lung cancers are discovered during routine physical examination or examination due to other diseases, and some of them are not early when discovered. There are various symptoms of lung cancer, none of which is unique to lung cancer and can be easily covered up by other acute and chronic lung diseases. There is no easy and simple method for lung cancer screening, such as checking a few drops of blood to determine whether there is a tumor, as people hope. 4. People’s awareness of health checkups still needs to be improved, and many people are still proud of not going to hospitals and not having checkups. Now it is advocated that normal people over 40 years old, especially those who smoke, have chronic lung disease, or are exposed to harmful substances such as chemical materials or minerals for occupational reasons, should have annual chest CT examination.