Figure 1.

Flat epithelial atypia: columnar cell change with atypia. (a) This terminal duct lobular unit shows variably dilated acini, many of which contain intraluminal secretions and calcifications. Most acini are lined by only one or two layers of columnar epithelial cells, many of which show prominent apical cytoplasmic snouts (hematoxylin & eosin, original magnification 10×). (b) The columnar epithelial cells lining the acini show cytologic atypia, characterized by enlarged, monotonous nuclei; the nuclear/cytoplasmic ratio is increased. Nucleoli are evident in some of the nuclei (hematoxylin & eosin, original magnification 40×).