title: Flat epithelial atypia of the breast.
abstract: Flat epithelial atypia is a presumably neoplastic alteration of terminal duct-lobular units that is characterized by the replacement of the native luminal epithelium by ductal cells demonstrating low-grade cytologic atypia. The atypical cells maintain a "flat" pattern of growth without evidence of architectural atypicality. Morphologic, immunohistochemical, and molecular investigations support that flat epithelial atypia represents an early step in the evolution of low-grade ductal carcinomas. It is frequently seen in association with atypical ductal hyperplasia, low-grade ductal carcinoma in situ, invasive tubular carcinoma, and lobular neoplasia. The risk for subsequent breast carcinoma remains to be defined, but flat epithelial atypia likely represents a nonobligate precursor with an extended time course to progression. Certain benign alterations may superficially mimic its appearance; careful attention to cytologic and architectural characteristics can help one distinguish these unrelated entities from flat epithelial atypia.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA 02114, USA. mlerwill@partners.org
authors.forename: Melinda F
authors.initials: MF
authors.lastname: Lerwill
mesh_terms: D001706:Biopsy; D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000175:diagnosis / Q000473:pathology; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000175:diagnosis / Q000473:pathology; D003937:Diagnosis, Differential; D004847:Epithelial Cells / Q000473:pathology*; D005260:Female; D006801:Humans; D006965:Hyperplasia / Q000175:diagnosis / Q000473:pathology; D010336:Pathology / Q000193:education*