Carcinoma derived from the lining epithelial cells in malignant phyllodes tumor is a rare neoplasm of the breast and belongs to the category of carcinosarcoma. We report a case of ductal carcinoma with squamous differentiation arising in malignant phyllodes tumor. A 54-year-old woman was admitted with a rapidly enlarging left breast mass. A breast tumor with a diameter of 6 cm was located mainly in the left outer area of the breast. Mammography revealed a high-density mass with an irregular margin and ultrasound showed a cystic tumor. A pathological diagnosis of ductal carcinoma with squamous differentiation was made by fine needle aspiration and a core needle biopsy. She underwent neoadjuvant chemotherapy followed by a modified radical mastectomy with a skin flap. Histopathological examination revealed that the invasive ductal carcinoma with squamous differentiation originated from the lining epithelial cells in malignant phyllodes tumor and that there was no transition area between the carcinomatous and the sarcomatous component. She experienced lung and facial bone metastases, microscopic features of which were consistent with the sarcomatous component of the original breast carcinosarcoma. This is an extremely rare case of carcinosarcoma and the histopathological findings and review of the literature are discussed.
2007 by The Japanese Breast Cancer Society