Mr. Jiang was admitted to the local hospital with unexplained headache, vomiting, aphasia, and hemiparesis. He had a history of smoking for more than 30 years. Cranial CT showed large cerebral infarction and he was transferred to a higher hospital. Further examination led to the final diagnosis of lung cancer complicating cerebral infarction. In fact, lung cancer with extrapulmonary manifestations is not rare. How can lung cancer be associated with cerebral infarction? One of the reasons is that in early stage of lung cancer, patients have increased coagulation factors, which puts the body in hypercoagulable state and easily induces cerebral thrombosis, thus causing stroke; in late stage of lung cancer, the cancer cells are transferred to brain tissues, which damages brain function, so as to make the patient suffer from hemiplegia and other symptoms. This suggests that we should not miss the chest examination in the process of diagnosis and treatment. The following extrapulmonary manifestations of lung cancer should also draw your attention. Hyponatremia: In 1938, experts firstly found that hyponatremia was related to lung cancer, among which small cell lung cancer accounted for 90%. It is related to the secretion of ectopic antidiuretics by tumor cells. It is called ectopic antidiuretic secretion syndrome. Its main manifestation is low blood sodium with urine concentration. Clinical encounter of unexplained intractable hyponatremia, especially for those with long history of smoking, should be highly alert to the possibility of lung cancer. Spontaneous pneumothorax Lung cancer may be complicated by pneumothorax because: the cancer invades the pleura under the peripheral pleura of the lung, leading to necrosis and pleura rupture; the cancer causes incomplete obstruction of bronchial tubes, and the alveoli at the distal end of the lungs rupture due to over-expansion; when the cancer obstructs the airway after having obstructive lung diseases or pulmonary alveoli in the past, the pulmonary alveoli may be induced to rupture. Lung cancer with pneumothorax as the first symptom is rare and easily neglected by clinic. Lumbar intervertebral disc herniation is the result of bone metastasis of lung cancer. From anatomical and physiological point of view, with rich blood flow in pulmonary circulation, lung cancer cells can reach the left atrium through pulmonary venous system, and then reach the whole body skeletal system with the blood flow in body circulation, resulting in bone metastasis. Therefore, lung cancer is one of the most common primary causes of bone metastatic cancer, which is often misdiagnosed as lumbar intervertebral disc herniation. Difficulty in swallowing Lung cancer combined with mediastinal lymph node metastasis may cause difficulty in swallowing. When encountering dysphagia in clinic, if the cause cannot be found in digestion, lung cancer should be thought of. Pericardial effusion Lung cancer may invade or metastasize to pericardium and cause large amount of pericardial effusion or even pericardial tamponade, which is fatal. Edema of upper limbs, neck and face Complete or incomplete obstruction of superior vena cava caused by various etiological factors may obstruct the return of blood from the superior vena cava, thus causing edema of upper limbs, neck and face, as well as superficial varicose veins of the upper body, among which bronchial lung cancer is the most common. In addition, patients with lung cancer may also have muscle weakness, dermatomyositis, anorexia, long-term persistent high fever, anemia with wandering embolic phlebitis, and abnormal penile erection. Clinicians should improve the identification of people at high risk for lung cancer.