Fine-needle aspiration cytology of ductal adenoma: report of a case associated with a mucocele-like lesion.

Ductal adenoma (DA) is an uncommon breast lesion that can histologically and clinically mimic carcinoma. We performed a fine-needle aspiration (FNA) of a DA. Cytologically, the lesion had features overlapping with those of mucinous carcinoma (MC), mucocele-like lesion, lactating adenoma (LA), and in retrospect with intraductal papilloma (IP). The smears were highly cellular and contained numerous monolayered sheets of ductal cells with prominent punched-out, small vacuoles distending the cytoplasm. The nuclei were mostly round to oval and had bland chromatin. Occasionally cells with enlarged nuclei and conspicuous nucleoli were present. The background showed large mucin pools, scattered single cells with mild nuclear atypia, some with apocrine metaplasia, rare stripped nuclei, and a fibrovascular stromal component. Calcifications were also present. We compare our cytologic findings with those of the lesions considered in the differential diagnosis. Due to its rare incidence and unusual features. DA may represent a diagnostic pitfall on FNA. Increased awareness of its cytologic appearance may help prevent a misdiagnosis.