Fine needle aspiration cytology of high grade mucoepidermoid carcinoma of the breast: a case report.

Background: Primary mucoepidermoid carcinoma of the breast is a very unusual tumor. It is often misdiagnosed, masquerading under different diagnoses. The cytologic assessment is especially difficult when the lesion is high grade. One reported case was initially diagnosed by fine needle aspiration cytology.

Case: A 69-year-old woman presented with a 6 x 4-cm tumor located in the upper outer quadrant of the right breast. The first cytologic diagnosis suggested ductal carcinoma with atypical squamous metaplasia; further review disclosed that the clusters of epithelial ductal cells displayed a mixed pattern of glandular, squamous and intermediate cells. There also was a scant intracellular and extracellular mucous substance, confirming the diagnosis of mucoepidermoid carcinoma. Histochemistry and immunohistochemistry, performed on the tumor and lymph node metastases, showed cellular staining for periodic acid-Schiff, and keratin, epithelial membrane antigen and carcinoembryonic antigen demonstrated the epithelial origin. The high expression of Ki-67, as well as the finding of 24 metastasized nodes in the axilla, demonstrated the tumor's aggressiveness.

Conclusion: Fine needle aspiration cytology is a very reliable tool in achieving a fast and accurate diagnosis of primary mucoepidermoid carcinoma of the breast.