Pancoast’s syndrome may be the result of neoplastic, inflammatory or infectious disease. We report an unusual case of Pancoast’s syndrome in a patient with metastatic breast cancer. A 54-year-old woman, affected by metastatic breast cancer, presented for severe shoulder pain, paraesthesia and numbness in the right arm. Despite further multiple lines of systemic chemotherapy, she developed a progressive enlargement of retropectoral, supraclavicular and infraclavicular lymph node metastases, which involved brachial plexus, apex of lung and anterior mediastinum. Physical examination revealed severe weakness of proximal muscles of the right arm. Neuropathic pain was managed with pharmacological treatment. Lastly, the patient has been treated with intrathecal analgesia with morphine and ziconotide with a good control of pain. The patient died after 3 months.