We recently encountered two patients who presented to orthopedics with lower extremity joint pain, resulting in a final diagnosis of confirmed lung cancer. Neither of the patients had ever had symptoms such as cough, hemoptysis or chest pain. This is exactly the complexity of the clinical manifestations of early lung cancer, the so-called extra-pulmonary manifestations of lung cancer. In a small percentage of lung cancer patients, signs and symptoms of extra-thoracic organs can appear before, during and after the discovery of lung cancer, which is now believed to be related to certain special hormones, antigens, enzymes or metabolites produced by lung cancer cells, and not related to direct tumor invasion. The rate of such extra-pulmonary manifestations generally occurs in about 10%. The main manifestations are as follows, which need to be noticed and detected in clinical practice to improve the early diagnosis of lung cancer 1. Systemic changes: mainly unexplained fever, anorexia, and cachexia; 2. Ectopic endocrine syndrome: commonly includes abnormal antidiuretic hormone secretion syndrome, which manifests as persistent hyponatremia and the manifestation of central nervous system disorder brought by it, most commonly in small cell lung cancer; and ectopic pro-adrenocorticotropic hormone syndrome, which manifests edema, hypertension, and weight loss, and may appear in the long term Cushing’s syndrome, commonly seen in small cell lung cancer; 3. Musculoskeletal changes: pestle and mortar fingers, hypertrophic pulmonary osteoarthropathy, showing symmetrical finger and toe swelling, symmetrical arthralgia, ankle, knee wrist and elbow joints are often involved, commonly seen in squamous carcinoma, adenocarcinoma and small cell lung cancer; 4. Neuroparaneoplastic syndrome: mostly seen in small cell lung cancer lung cancer, commonly There are myasthenia gravis syndrome, subacute cerebellar degeneration, encephalomyelitis-subacute sensory neuropathy, limbic encephalitis, etc. 5.Other: deep vein thrombosis, pulmonary artery thromboembolism, non-bacterial thrombotic endocarditis, polymyositis, dermatomyositis, scleroderma, etc. As it can be seen, the extra-pulmonary manifestations of lung cancer are complex and diverse, which can be easily confused with endocrine, orthopedic and neurological diseases.