Abstract
Acinic cell carcinoma (ACC) of the breast is extremely rare and is characterized by widespread acinar cell-like differentiation. We report of a 39-year-old woman presented with a palpable breast mass with significant morphological, immunohistochemical and ultrastructural findings. Histologically, ACC showed a diffuse glandular infiltrative pattern, with small acinar or glandular structures mixed with solid nests. Neoplastic cells were monotonous proliferation of cells with a granular or clear cytoplasm, resembling acinar cells of the salivary glands or Paneth cells. Both glandular and solid tumor cell populations were strongly positive for lysozyme and α-1-antitrypsin.