Flat ductal epithelial atypia

A breast lesion characterized by the presence of dilated terminal ductal lobular units in which the epithelial lining has been replaced by a single layer of mildly atypical cells, or there is atypical, monotonous epithelial hyperplasia of three to five layers. This lesion relates to columnar cell change with atypia and columnar cell hyperplasia with atypia.