Microglandular adenosis of the breast. A clinicopathologic study of 11 cases with ultrastructural observations.

The clinical and pathologic features of 11 examples of microglandular adenosis of the breast are presented. Microglandular adenosis is a rare, benign lesion that is easily confused with carcinoma. It is characterized by a concentrated proliferation of round glands with open lumens in a densely homogeneous stroma that clearly delineates microglandular adenosis from the adjacent uninvolved breast. The glands are lined by a single layer of cells with distinctly vacuolated or granular cytoplasm. Ultrastructurally, the single layer of epithelial cells lacks cytoplasmic protrusions and is surrounded by a thick multilayered basement membrane. Light- and electron-microscopic features that help distinguish microglandular adenosis from well-differentiated (tubular) carcinoma and sclerosing adenosis, entities with which it is easily confused, are discussed.