Described are two epithelial lesions of the breast displaying extremely rare, widespread acinic cell-like differentiation (metaplasia). Two women, 70 and 40-year-old, one with invasive ductal papillocarcinoma, the other one with conventional intraductal hyperplasia without atypia, both demonstrated massive diffuse, PAS positive, granular eosinophilic transformation of the cell cytoplasm. This unusual cell appearance closely simulated acinar cells in normal serous salivary gland/acinic cell carcinoma or Paneth cells. Both extensive expression of lysozyme and finding of numerous zymogen granules ultrastructurally confirmed the acinic cell-like fenotype. Discussed is differential diagnosis of the breast neoplasm containing overt eosinophilic and granular cytoplasm. Reviewing literature and comparing our unique finding of unusual salivary-type differentiation in conventional ductal hyperplasia of the breast, biologic implications are considered.

        Key words: breast – acinic cell-like carcinoma – salivary gland-like carcinoma – ductal hyperplasia – differentiation