A 32-year-old woman presented with 3 months' history of rapid enlargement of the left breast and superficial ulceration. Staging F-18-FDG PET/CT performed after admission demonstrated a hypermetabolic mass in the left breast, with smaller hypermetabolic areas in the left axillary and internal mammary lymph nodes, as well as in the sternum. Postoperatively, the mass was diagnosed as metaplastic squamous cell carcinoma of the breast.