Because of a situation encountered a few days ago, the patient had already had radiotherapy for NPC many years ago, and this time, coughing and hemoptysis were found on CT with tumor in the inner left lung, and the office hilar lymph nodes were a bit large. Therefore, it is important whether the lung is metastatic to NPC or not. After careful identification it was considered as primary lung cancer occurring in the lung and not metastasis. The thoracic surgeon also looked at it and recommended surgery. There are the following ways to differentiate whether it is primary lung cancer 1. Medical history: primary cancer occurs first in the lung and there is no tumor in other organs, or although there is tumor in other organs, the lesion in the lung is confirmed as the primary foci by pathological examination. In contrast, metastatic cancer occurs after tumors of other organs, and its tissue type is basically the same as that of the primary cancer; 2. Course of disease: certain primary cancers grow rapidly and are prone to lymphatic or hematogenous metastasis, while metastatic cancer develops slowly and is not easy to metastasize again; 3. Symptoms: primary lung cancer has obvious symptoms such as cough, chest pain and bloody sputum, while metastatic cancer has no obvious symptoms; 4. burr or lobulation, usually single, this is more important, and if it is squamous cancer tumor is mainly in the medial band of lung. Metastatic cancer, on the other hand, is more frequent, and metastatic lesions are often found in multiple places of the lung, and the location is often in the outer band. They are round in shape, with neat edges, complete envelope and often multiple; 5. Cytological examination: cancer cells can be easily detected in the sputum of primary cancer, while the detection rate of metastatic cancer is extremely low; 6. Prognosis: the prognosis of primary cancer is poor, while the prognosis of metastatic cancer changes with the primary foci.