ORIGINAL ARTICLESMicroglandular Adenosis With Transition Into Adenoid Cystic Carcinoma of the BreastAcs, Geza M.D., Ph.D.; Simpson, Jean F. M.D.; Bleiweiss, Ira J. M.D.; Hugh, Judith M.D.; Reynolds, Carol M.D.; Olson, Sandy; Page, David L. M.D.Author Information From the Department of Pathology and Laboratory Medicine (G.A.), University of Pennsylvania Medical Center, Philadelphia, Pennsylvania; Department of Pathology (J.F.S., S.O., D.L.P.), Vanderbilt University Medical Center, Nashville, Tennessee; Department of Pathology (I.J.B.), Mount Sinai School of Medicine, New York, New York; Department of Pathology (C.R.), Mayo Clinic, Rochester, Minnesota, U.S.A.; and Department of Pathology (J.H.), Cross Cancer Institute, Edmonton, Alberta, Canada. Presented in part at the 91st Annual Meeting of the United States and Canadian Academy of Pathology, Chicago, IL, February 23 to March 1, 2002. Address correspondence and reprint requests to Geza Acs, MD, PhD, Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, 6 Founders Pavilion, 3400 Spruce Street, Philadelphia, PA 19104, U.S.A.; e-mail: [email protected] The American Journal of Surgical Pathology: August 2003 - Volume 27 - Issue 8 - p 1052-1060 Buy Abstract Microglandular adenosis (MGA) is a well-recognized, if rare and incompletely characterized, entity in which carcinoma is rarely thought to develop. We report 17 cases in which patterns of adenoid cystic carcinoma (ACC) coexisted with MGA. Immunocharacterization with β-catenin, E-cadherin, cytokeratins (AE1/AE3), epithelial membrane antigen, S-100 protein, smooth muscle actin, and vimentin was also performed. Most cases had areas of invasive ACC characterized by its defining dual-lumen types. Some cases of ACC appeared to have expanded glands intermingled within the MGA, whereas in other cases ACC formed a transition with the characteristic small, gland-like spaces of MGA. MGA and “atypical MGA” stained irregularly and similarly to that seen in myoepithelium with the three markers of myoepithelial cells in breast: S-100 protein, smooth muscle actin, and vimentin. These markers were also positive in the more solid elements of the ACC. Our study suggests that ACC may develop in a background of and in continuity with MGA. Altered myoepithelial cells appear to be the major neoplastic element in both ACC and “atypical MGA.” “Atypical MGA” with transition to ACC may show histologic patterns and an immunohistochemical profile similar to that of ACC. These lesions might be best interpreted as ACC in situ. Both MGA and ACC of the breast grow in an expansile and diffusely infiltrative pattern without having significant metastatic capacity. Their unusual interaction with the surrounding stroma may play a role in this benign biologic behavior. © 2003 Lippincott Williams & Wilkins, Inc.