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flat epithelial atypia

Tuesday 7 August 2012


Definition: Flat epithelial atypica is a proliferation of epithelial cells in the terminal duct-lobular units (TDLU) of the breast.

FEA shows one to two columnar cell layers within the duct, with mild atypia and apical snouts. It is associated with tubular and lobular carcinomas.


- FEA is just DCIS without the architecture

Sometimes this neoplasm is called ‘columnar cell hyperplasia‘ due to the architecture of the growth pattern.

It tends to grow in a ‘flat‘ pattern, without any strange build-ups or unevenness, and tends to grow into ‘columns‘; growing taller without growing wider.

Flat epithelial atypica can grow to a thickness of 5 or 6 epithelial cells, as opposed to the normal thickness of the breast duct lining of about 2 cells.

It is generally considered to be a benign neoplasm, although there is still some debate as to whether or not flat epithelial atypica is associated with a very low grade ductal carcinoma in situ.

There can also be functional breast complications with flat epithelial atypia as it does tend to cause the terminal duct lobular units to become distended, and to partially or fully block breast ducts.

Differential diagnosis

- Flat epithelial atypia (FEA) of the breast

  • Flat epithelial atypia (FEA) of the breast typically is a localized alteration involving only few, neighboring terminal ducto-lobular units.
  • However, occasionally there are cases with extensive FEA and morphologic evidence of direct transitions between FEA and classical low-grade ductal carcinoma in situ (lg-DCIS).
  • There is a direct transitions between FEA and lg-DCIS and FEA can be considered as a part of the low-grade pathway in the development of breast cancer.

See also

- mammary epithelial atypia
- mammary columnar cell anomalies


- Transitions Between Flat Epithelial Atypia and Low-grade Ductal Carcinoma In Situ of the Breast. Aulmann S, Braun L, Mietzsch F, Longerich T, Penzel R, Schirmacher P, Sinn HP. Am J Surg Pathol. 2012 Aug;36(8):1247-52. PMID: 22790863