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Surgical Pathology Criteria

Flat Epithelial Atypia of the Breast


  • Breast epithelial proliferation of 1-5 cell layers composed of cells with low-grade nuclear atypia but with architectural features not meeting the criteria for ductal carcinoma in situ

Alternate/Historical Names

  • Columnar cell alteration with prominent apical snouts and secretions (CAPSS) with atypia
  • Columnar cell change with atypia
  • Columnar cell hyperplasia with atypia

Diagnostic Criteria

  • Flat growth pattern
    • Proliferative epithelium 1-5 cell layers thick
    • Architectural complexity falls short of low grade DCIS and ADH (atypical ductal hyperplasia)
      • No partial or complete filling of ducts
      • Arcades and micropapillary formations absent or very rare
      • Tufts and mounds may be seen
    • Involves distended terminal duct lobular units
  • Low grade nuclear atypia
    • Nuclei 2-3x size of a RBC (10-15 microns)
    • Minimal pleomorphism
    • Short of high grade DCIS
  • Lined by cuboidal to round cells
    • Frequently with eosinophilic cytoplasm
    • Frequently with prominent apical snouts
  • Columnar cell change and hyperplasia (lesions without nuclear atypia) are considered separately

Kristin C Jensen MD
Richard L Kempson MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: January 16, 2007

Supplemental studies


  • No diagnostically useful markers are currently reported

Genetic Analysis

  • No diagnostically useful markers are currently reported

Flat epithelial atypia is likely a precursor of low-grade DCIS and shares markers and genetic changes

  • ER and PR frequently positive
  • bcl2 positive
  • Loss of heterozygosity at similar loci

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


  • May be associated with or adjacent to ductal carcinoma in situ, lobular carcinoma in situ and/or invasive carcinoma
  • The finding of flat epithelial atypia on a needle core biopsy warrants an excisional biopsy because of the frequent (15-30%) association with worse lesions on excision

Grading / Staging / Report


  • Flat epithelial atypia is not graded, although many pathologists prefer to categorize the atypia into mild, moderate and severe degrees


  • Not applicable


  • Needle core biopsies
    • Because of the frequent association with worse lesions on excision, a recommendation for excisional biopsy should be included in the pathology report when flat epithelial atypia is identified in a needle core biopsy
  • Excisional biopsies
    • The significance of flat epithelial atypia in an excisional biopsy and/or at a surgical margin of an excisional biopsy is not yet established
    • It is currently recommended that flat epithelial atypia not be taken into account in size measurement of ductal carcinoma in situ and not be reported as a positive margin when present at the margin of a ductal carcinoma in situ excisional biopsy
    • The finding should be noted in the report



Intraductal and Intralobular Proliferative Lesions


  • Tavassoli FA, Hoefler H, Rosai J, Holland R, Ellis IO, Schnitt SJ, Boecker W, Heywang Köbrunner SH, Moinfar F, Lakhani SR. Intraductal proliferative lesions. In: Tavassoli FA, Devilee P, editors. Pathology and genetics: tumours of the breast and female genital organs. Lyon, France: IARC Press, 2003, pp. 63-73.
  • Schnitt SJ. Flat epithelial atypia classification, pathologic features, and clinical significance. Breast Cancer Res 2003;5:263-8.
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