Columnar Cell Lesions and Flat Epithelial Atypia of the Breast

Lesions of the breast characterized by enlarged terminal duct lobular units lined by columnar epithelial cells are being encountered increasingly in breast biopsies performed because of mammographic microcalcifications. Some of these lesions feature banal columnar cells in either a single layer (columnar cell change) or showing stratification and tufting but without complex architectural patterns (columnar cell hyperplasia). In other columnar cell lesions, the lining cells exhibit cytologic atypia, most commonly of the low-grade, monomorphic type. Such lesions were included among lesions originally categorized by Azzopardi as “clinging carcinoma” (monomorphic type), and were more recently included among lesions designated “flat epithelial atypia” (FEA) by the World Health Organization Working Group on Tumors of the Breast. The role of columnar cell lesions and, in particular, FEA in breast tumor progression is still emerging. FEA commonly coexists with well-developed examples of atypical ductal hyperplasia, low-grade ductal carcinoma in situ, and tubular carcinoma. These findings, in conjunction with the results of recent genetic studies, suggest that FEA is a neoplastic lesion that may represent either a precursor to or the earliest morphological manifestation of DCIS. However, the few available clinical outcome studies suggest that the risk of progression of FEA to invasive cancer is extremely low, supporting the notion that categorizing such lesions as “clinging carcinoma” and managing them as if they were fully developed DCIS will result in overtreatment of many patients. Additional studies are needed to better understand the biological nature and clinical significance of these lesions.