Breast - nonmalignant
Atypical hyperplasia
Flat epithelial atypia of breast

Topic Completed: 1 October 2014

Revised: 11 December 2019

Copyright: 2002-2019,, Inc.

PubMed Search Flat epithelial atypia [title] breast

Jaya Ruth Asirvatham, M.B.B.S.
Julie M. Jorns, M.D.
Page views in 2019: 7,407
Page views in 2020 to date: 1,111
Cite this page: Asirvatham JR. Flat epithelial atypia of breast. website. Accessed February 20th, 2020.
Definition / general
  • Replacement of epithelium by up to 5 layers of mildly atypical cells, presumably neoplastic
  • Introduced by WHO Working Group on Pathology and Genetics of Tumours of the Breast to encompass columnar cell lesions with low grade / monomorphic cytologic atypia that lacked architectural features of ADH or low grade DCIS
  • Also called atypical columnar change (columnar cell change with atypia or columnar cell hyperplasia with atypia), flat ductal intraepithelial neoplasia grade 1A (DIN1A), low grade clinging carcinoma monomorphous type, atypical columnar alternation with prominent apical spouts and secretions, columnar cell change with atypia
  • Biology still being investigated - may be an early neoplastic breast lesion (Semin Diagn Pathol 2010;27:37)
  • Mitochondrial DNA sequencing and phylogenetic tree clustering revealed direct transitions between FEA and LG DCIS in 10 of 10 cases, supporting the interpretation of FEA as part of the low grade pathway in the development of breast cancer (Am J Surg Pathol 2012;36:1247)
Clinical features / prognostic factors
Microscopic (histologic) description
  • Atypia that does not fulfill criteria of ADH or low grade DCIS
  • Distention of terminal duct lobular unit (TDLU); usually more blue than normal TDLU at low power
  • Replacement of epithelial cells by single or stratified layer of cells with low grade cytologic atypia resembling low grade DCIS
  • Flat growth pattern usually resembles blunt duct adenosis; cells are not regularly oriented perpendicular to basement membrane
  • Also cystically dilated ducts with secretions or apocrine features (apical snouts)
  • Nuclei are usually round with variably prominent nucleoli
  • Often calcifications
  • Usually no / rare micropapillary formations
Microscopic (histologic) images

Contributed by Dr. Mark R. Wick:

Various images

Images hosted on other servers:

Various images

Compare to blunt duct adenosis

Columnar cell change

Variably dilated acini

Low grade cytologic atypia

Positive stains
Negative stains
Molecular / cytogenetics description
  • Phosphatidylinositol 3 kinase catalytic subunit (P13KCA) mutations frequently observed similar to other breast epithelial proliferations (Mod Pathol 2014;27:740)
  • Does not share similar molecular profiles of p16 (INK4a) epigenetic modification with atypical ductal hyperplasia and low grade ductal carcinoma in situ (Hum Pathol 2008;39:1637)
  • Clonally related to invasive tubular carcinoma (Am J Surg Pathol 2009;33:1646)
Differential diagnosis
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