Lung cancer is late stage once it is detected mainly because the clinical manifestations of lung cancer are very complex, and the typical symptoms and signs are often already in the advanced stage of the disease when they appear. If clinicians can fully grasp the clinical characteristics of lung cancer, especially be alert to the suggestive early manifestations, it is possible to obtain diagnosis at an early stage of lung cancer. In actual clinical work, early diagnosis of lung cancer is difficult because most patients do not have any symptoms in the early stage of the tumor, and even those who have symptoms are easily confused with pre-existing symptoms or signs due to the non-specific nature of their clinical manifestations, thus affecting the timely acquisition and correctness of diagnosis.