Adenoid cystic carcinoma of the breast: diagnosis by fine-needle aspiration.

Adenoid cystic carcinoma rarely occurs as a primary breast malignancy. When seen in fine-needle aspiration (FNA) material, it is identical to its counterpart in the salivary glands. We report six cases diagnosed by aspiration in patients aged 32-82 yr. The smears were highly cellular and featured extracellular spheres of metachromatic material. These were surrounded by small, uniform cells with bland nuclei and very little cytoplasm. Numerous similar cells occurred singly in the background. The cytologic differential diagnosis of adenoid cystic carcinoma includes other entities that produce extracellular metachromatic spheres including collagenous spherulosis. We describe and illustrate similar material originating in inspissated secretions or stromal fragments from fibrocystic change and fibroadenoma, as well as infiltrating ductal carcinoma. Diagnostic criteria for adenoid cystic carcinoma and the clinical relevance of distinguishing this rare tumor from typical infiltrating ductal carcinoma are discussed.