Left shoulder pain may be cancer, but other benign diseases such as frozen shoulder may also cause soreness in the left shoulder. Clinically, some cancer patients do have left shoulder pain, when the cancer invades the left shoulder, it can be bones, lymph nodes and the surrounding soft tissues, invading these tissues can lead to left shoulder pain, for example, breast cancer metastasizes to the lymph nodes on the left supraclavicular region, when the lymph nodes are enlarged, it can cause left shoulder pain when the lymph nodes are enlarged, and compressing the nerves in the left shoulder. Of course, left shoulder pain can also be caused by other benign diseases, such as frozen shoulder, patients usually also have left shoulder pain. Overall, left shoulder pain is a non-specific manifestation, not unique to certain diseases, and needs to be combined with other symptoms to identify the disease. Frequent occurrence of left shoulder pain is recommended to go to the hospital in time to find out the cause of the disease and treat it.