Surgical Pathology Criteria–

Flat Epithelial Atypia of the Breast

Differential Diagnosis

Flat Epithelial Atypia Columnar Cell Change / Hyperplasia
Enlarged atypical ovoid to round nuclei Bland oval to elongate nuclei
Chromatin may be marginated Bland chromatin
Nucleoli may be prominent Nucleoli not prominent
Basal polarization of nuclei usually lacking Nuclei usually basally polarized
Frequently more abundant cytoplasm Moderate amount of cytoplasm

Low Grade Ductal Carcinoma In Situ and Atypical Ductal Hyperplasia Flat Epithelial Atypia
Architectural complexity manifested by a) partial or complete filling of ducts or b) arcades or micropapillary formations Lacks architectural complexity
All three have low grade nuclear atypia, except for some cases of ADH, which must have architectural complexity

High Grade Ductal Carcinoma In Situ Flat Epithelial Atypia
Grade III nuclear atypia Low grade nuclear atypia
Frequent comedonecrosis Lacks comedonecrosis

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