Patients with left shoulder pain will need a pathologic biopsy and other tests in order to determine if it is cancer. Multiple causes can cause left arm pain, such as cervical spondylosis, overexertion, bruises, and lipoma. If the shoulder pain is caused by metastatic spread of cancer, it is usually to have the symptoms of the primary tumor, such as swelling, pain, and mass in the affected area. Patients with shoulder pain who have lumps in the affected area can do pathological biopsy to confirm whether it is cancer or not, and pathological examination is the gold standard for diagnosing cancer. Other related tests such as ultrasound and tumor markers can also be done to assist in determining whether it is cancer or not. Shoulder pain alone cannot be used to determine whether it is cancer or not. Patients with left shoulder pain should actively seek medical treatment, and patients should not treat themselves to avoid adverse results.