A 38-year-old woman with metastatic breast cancer presents with severe cancer pain (VAS 9/10) localized to the right chest wall and axilla. She is currently on morphine 60 mg twice daily (total 120 mg/day) but reports inadequate pain control despite good compliance. She denies nausea, constipation, or sedation. Physical examination reveals a firm, fixed mass in the right breast with axillary lymphadenopathy. What is the most appropriate next step in opioid management?