Left shoulder pain may be an early manifestation of some cancers, such as osteosarcoma. However, it may also be related to other reasons, such as cervical spondylosis, frozen shoulder, left shoulder trauma, etc. It is not absolutely early cancer, therefore, it needs to be divided into situations and cannot be generalized. 1. Osteosarcoma: Osteosarcoma is a kind of tumor disease with high malignant degree, and adolescents are the high incidence group. In the early stage, there will be symptoms of bone pain, such as dull pain in the shoulder and knee joints, which will be accompanied by restricted movement of the shoulder joints and swelling of the shoulder. 2. Cervical spondylosis: If you have cervical spondylosis, it can also cause left shoulder pain, which is mostly seen in neurogenic cervical spondylosis, which is mainly caused by nerve root compression, resulting in radiating pain in the left shoulder; in addition to this, spinal cervical spondylosis can also cause left shoulder pain, which can be accompanied by radiating pain in the back and chest. 3. Frozen shoulder: Most of the cases are due to acute injury of the shoulder and prolonged over-activity, due to the aseptic inflammation of the shoulder joint, the surrounding soft tissues are stimulated, and then the left shoulder pain will appear. 4. Trauma to the left shoulder: If the left shoulder is accidentally hit by external force or impact, resulting in fracture, left shoulder pain will also occur. Therefore, although left shoulder pain may be seen in the early stage of some kind of cancer, it is not absolute, and it may be caused by other factors; it is recommended to go to the hospital in time to find out the cause and take active treatment, so as to avoid delaying the condition.