Phyllodes tumor of the breast, or cystosarcoma phyllodes, is an unusual breast tumor. It is usually considered a benign lesion but may have malignant potential. Only a small proportion of malignant phyllodes tumors will metastasize. A phyllodes tumor of the breast metastasizing to the pancreas is rare. This 39-year-old female patient initially presented to us with a 5 x 4 x 2 cm tumor of a right breast. After excision of the tumor, she received another wise excision for a local recurrence of the tumor. Three years had passed when she started having hematemesis and tarry stools intermittently over a period of about one month. Clinical evaluation disclosed a huge mass with an ulcerated and bloody base over the second portion of the duodenum. A pancreatoduodenectomy was then performed. During the postoperative recovery period, a rapidly enlarging tumor of the right breast was noted. She subsequently underwent a total mastectomy of the right breast. Both the duodenal tumor and the breast tumor were found to be malignant phyllodes tumors. The rarity of this kind of patient and presentation is discussed.