Explicitly considering lung CA does not necessarily mean lung cancer. Clinically, patients will be considered as having lung cancer possibility based on clinical symptoms such as recurrent paroxysmal severe cough, blood in sputum or hemoptysis, chest pain, wasting and elevation of blood tumor markers, and when CT imaging of lung suggests lung occupancy. These bases can only be used as the basis of auxiliary diagnosis, but not as the basis of confirming the diagnosis. Even if PET-CT examination is considered to be lung cancer, it only indicates that there is 80%-90% probability of lung cancer, and still cannot confirm the diagnosis. Clinically, lung cancer can be diagnosed by bronchoscopy, percutaneous lung puncture biopsy and thoracoscopic biopsy, etc. Only when cancer cells are found in pathological examination, lung cancer must be lung cancer.