A rotator cuff tear causes shoulder pain and limits movement of the shoulder joint. A chronic degenerative change or impingement is the reason for a rotator cuff tear. Diagnosis is made based on medical history and, physical and radiological examinations. Other causes of shoulder pain include calcific tendinitis, degenerative arthropathy, joint dislocation, fracture, and primary or metastatic neoplasm. However, metastatic cancer in the shoulder joint is difficult to diagnosis. We experienced a case in which a 46-year-old female patient complained of left shoulder pain and limited joint mobility, and these symptoms were due to metastatic breast cancer in the shoulder.