Left shoulder and back pain may be caused by the following cancers: 1. lung cancer, tumors in the lung can cause shoulder and back pain, especially those occurring at the tip of the lung. 2. esophageal cancer, esophageal cancer can also cause back pain in the left shoulder. 3. leukemia, shoulder and back pain can also occur when there is infiltration of bone marrow and bone. 4. bone metastasis of liver cancer and bone metastasis of breast cancer can cause shoulder and back pain and other symptoms. How to differentiate: 1. Bone scan or bone CT is mainly performed to find bone with bone destruction. 2. PET-CT examination of the whole body is done to find the primary lesion. For specific clarification, a pathological puncture biopsy of the bone destruction site is required.