A case of malignant phyllodes tumor of the breast with osteosarcomatous features.

A 64-year postmenopausal woman had noticed a left breast lump 5 months before presentation and was admitted due to increasing tumor size. Physical examination showed a well demarcated, movable mass 5 cm in diameter in the upper outer quadrant of the left breast. The lesion was not painful. She had no past history of malignancy or chest wall irradiation. She had no family history of malignancy. Mammography revealed an irregular tumorous lesion with coarse calcifications in the left breast. Intracystic papillary cancer was suspected by ultrasonography. Aspiration breast cytology yielded insufficient material for diagnosis. Laboratory findings were all within the normal limits including alkaline phosphatase and three tumor markers (CEA, CA 15-3, ST-439). An excisional biopsy of the left breast tumor was performed. Histopathological examination revealed malignant phyllodes tumor with osteosarcomatous features and negative tumor margins. Positive vimentin and negative cytokeratin staining was confirmed by immunohistochemistry, suggesting that the tumor did not originate from epithelial cells of the breast. The estrogen receptor (ER) status of the tumor was negative but progesterone receptor (PgR) was weakly positive. Positive p53 nuclear immunoreaction but negative c-erbB-2 overexpression by immunohistochemical staining was observed in this tumor. There was no evidence of generalized disease. She has been well 6 months after surgery without adjuvant therapy.