Knee pain is usually not present in the early stages of lung cancer. A small portion of lung cancer patients develop knee joint pain because of lung-derived osteoarthritis hyperplasia. Lung cancer is a malignant tumor originated from bronchial mucosa or glands in the lungs. Early symptoms of lung cancer are atypical, and patients mostly have cough, fever, chest tightness and chest pain, and seldom have knee joint pain. However, some special active substances produced by some lung cancers will cause periosteal hyperplasia of distal end of long bones and formation of new bones, resulting in symptoms of swelling and pain in affected joints. If bone metastasis occurs in patients with advanced lung cancer, the metastatic tumor will compress the nerve root innervating the knee joint, resulting in serious edema of the nerve root, which will lead to the symptoms of knee joint pain. Patients with knee joint pain in early stage of lung cancer should go to regular hospitals, undergo examination to clarify the cause of the disease, and then carry out treatment under the guidance of doctors.