Phyllodes tumors (PTs) are rare but complex fibroepithelial lesions of the breast. The present report describes an unusual case of a giant malignant PT with a rich blood supply treated with dominant blood supply internal thoracic artery interventional embolization before surgery. A 41-year-old woman without underlying systemic disease presented with a tumor >20 cm in diameter growing rapidly in the left breast. Radiological results indicated a giant circular tumor with a clear boundary occupying the whole breast, possible invasion of the major pectoralis muscle and several enlarged lymph nodes in the left axillary region. Computed tomography angiography showed a large mass with a rich and powerful blood vessel supply and preoperative interventional embolization was performed to block the internal thoracic artery. Three days after artery embolization, mastectomy and grade I axillary lymph node dissection were performed. The giant tumor measured 17x16x11 cm. The surgery successfully treated the pain and tumor necrosis and the patient received chemotherapy and local radiotherapy. No recurrence was found at the 14-month follow-up.