Fine-needle aspiration cytology of mammary adenomyoepithelioma: report of a case with intranuclear cytoplasmic inclusions.

Adenomyoepithelioma of the breast is an uncommon lesion which may recur and rarely metastasizes. We report the fine-needle aspiration (FNA) findings in one case of mammary adenomyoepithelioma in which this tumor's unusual cytomorphology led to a cytologic diagnosis of malignancy, possible metastatic to the breast. Large, atypical, polygonal cells, some with intranuclear cytoplasmic inclusions, were most worrisome cytologically, but corresponded in the biopsied specimen to cells immunohistochemically documented to be of myoepithelial origin. Nests of epithelium and myoepithelial cells sometimes embedded in fibrous, stromal fragments were suggestive of an infiltrating pattern. Recognition of such unusual features in breast FNA is most important since definitive therapy may follow an FNA diagnosis of carcinoma in some clinical settings. In cases with unusual morphology, surgical biopsy should be recommended to clarify the nature of the lesion.