A case of intracystic carcinoma of the breast: the importance of measuring carcinoembryonic antigen in aspirated cystic fluid.

We report a case of intracystic carcinoma of the breast in which a correct preoperative diagnosis was achieved on the basis of an increased level of carcinoembryonic antigen (CEA) in the aspirated cystic fluid. A 62-year-old woman was admitted with a 10 x 10 cm painful mass occupying the right breast. Ultrasonography revealed a cystic lesion with papillary projections arising from the cyst wall. Cytological examinations showed no malignant cells in the hemorrhagic aspirated fluid. However, the CEA level in the fluid was 5.5 times higher than the serum CEA level using a murine anti-CEA monoclonal antibody. The high level of CEA led to the preoperative diagnosis of intracystic carcinoma. Histological examinations confirmed the diagnosis of intracystic carcinoma after a modified radical mastectomy. Immunohistochemical staining by an anti-CEA monoclonal antibody elicited a strong positivity with diffuse intracytoplasmic distribution in the carcinoma cells, although heterogeneity of staining was observed. It is suggested that the measurement of the CEA value by anti-CEA monoclonal antibody in the aspirated fluid is easy, safe, and helpful for the definitive diagnosis of intracystic carcinoma of the breast.