Lung shadow refers to the shadow of a lump or mass found in X-ray chest film, chest CT and other imaging examinations. Once a lung shadow is detected, many people’s first guess is “lung cancer”, and many people even talk about “shadow” with fear. However, lung shadow is not equal to lung cancer. Common diseases with shadows in the lungs include pneumonia, tuberculosis, inflammatory pseudotumor, pulmonary isolation, silicosis, pulmonary fibrosis, COPD, lung cancer (peripheral lung cancer), and so on. For early detection of lung cancer, regular checkups are required. In addition to the routine chest X-ray, regular checkups should include tests specifically designed to diagnose lung cancer. The purpose of this is to screen for “people who may have abnormalities in their lungs. When we see a lung shadow on an x-ray, we cannot say “it is lung cancer”, but we cannot rule out the possibility of lung cancer either. Therefore, if a lung shadow is found, it is not necessary to blindly fall into lung cancer panic, nor is it easy to think that it is inflammation or benign tumor and delay the treatment. Patients should go to a regular hospital for scientific examination in time, and then be judged by an experienced doctor. The examination means include X-ray chest film, chest CT, tumor markers, magnetic resonance imaging (MRI), sputum exfoliated cells, fiberoptic bronchoscopy, positron emission tomography (PET) scan, check lung puncture biopsy, etc., which should be chosen according to the situation. The following three groups of people are at high risk of lung cancer and should have regular medical checkups, pay attention to active prevention, and not take it lightly if lung shadows are found: ① long-term smokers, those who have smoked for more than 20 years, those who smoke more than 20 cigarettes a day, and their passive smoking family members; ② those who are over 40 years old; ③ those who have a family history of heredity. These three groups of people should preferably include a CT scan of the lungs as a mandatory test during their normal physical examination in order to detect small lung nodules in a timely and accurate manner. If common symptoms of lung cancer such as chest pain, unexplained blood in sputum, weight loss and weight loss occur, prompt medical consultation is required.