Some insidious tumors, especially breast and lung cancer, can cause polyarthritis. Tumor polyarthritis often occurs in the elderly, and the affected joints are mostly asymmetrical. Small joints of the hands and wrists are rarely involved, and the blood sedimentation is often increased, but the imaging of the joints is normal. Arthritis can occur between or at the same time as tumors, and its pathogenesis is not clear. In clinical practice, patients who are hospitalized for joint pain, redness, swelling, and limitation of movement are sometimes seen, only to be diagnosed with malignancy after examination. At first glance, it seems that arthritis and tumor are simply unrelated to each other, but in fact, they are not. However, the arthritic symptoms and signs of these tumor patients are a special early clinical manifestation of some malignant tumors. Recent studies have shown that some malignant tumors that do not originate from endocrine glands or tissues can also secrete ties or proteins that resemble the functions of various hormones. Scientists call such abnormal secretions that are not secreted by endocrine glands or tissues “heterologous hormones”. Various malignant tumors such as lung cancer and gastric cancer can secrete heterologous growth hormone, which can stimulate bone and joint enlargement, swelling and pain, presenting hypertrophic osteoarthropathy, similar to acromegaly. This kind of osteoarthrosis can appear earlier than the symptoms of the primary lesion, and if the patient is treated as arthritis only, it is bound to be misdiagnosed and delayed.