Other carcinoma subtypes, not WHO classified


Topic Completed: 1 September 2012

Minor changes: 19 March 2021

Copyright: 2001-2022,, Inc.

PubMed search: myoepithelial carcinoma[title] breast

Monika Roychowdhury, M.D.
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Cite this page: Roychowdhury M. Myoepithelial. website. Accessed January 21st, 2022.
Definition / general
  • Rare tumor composed solely of cytologically malignant myoepithelial cells with mitotic activity
  • Also called malignant myoepithelioma
  • Median age 60 years
Prognostic factors
Case reports
  • Complete excision with negative margins
Gross description
  • Up to 21 cm, well defined with focal marginal irregularity and may be stellate
  • Large tumors may have hemorrhage and necrosis
Microscopic (histologic) description
  • Infiltrating spindle cells with fibrillar eosinophilic cytoplasm
  • Tumor appears to arise from myoepithelial cells of ductules at periphery of lesion
  • Cells have variable atypia
  • Mitotic figures common, but may be less than 4/10 HPF
  • May have clear cells (Tohoku J Exp Med 2003;200:103), due to glycogen (J Clin Pathol 1997;50:700)
  • May have necrosis
  • Infiltrative growth pattern most frequently with thin anastomosing cords of tumor cells associated with an intimately admixed reactive spindle cell stroma (Virchows Arch 2010;457:337)
Microscopic (histologic) images

Case #407


CK 5/6+

pan CK

Ki67 (high index)


PR+ (weak)


Images hosted on other servers:

Irregular dense proliferation of pleomorphic spindle cells

Tumor cells invade normal breast tissue

Figs 3E & 3F: adenomyoepithelioma with spindle cell elements & epithelioid cell elements


Various images

Cytology description
  • Cohesive cell groups composed of spindle cells with atypical cigar shaped nuclei
  • Also epithelioid cells, mitotic figures
Cytology images

Images hosted on other servers:

Crowded haphazard
cluster of cells
in metachro-
matic stroma

Nest of pleomorphic cells
is composed of large
epithelioid, plasmacytoid
and spindle cells

Positive stains
Negative stains
Electron microscopy description
  • Perinuclear tonofilaments, subplasmalemmal bundles of microfilaments with dense bodies, intermediate junctions, poorly developed desmosomes, pinocytic vesicles and fragmented external lamina (Int J Surg Pathol 2002;10:281)
Differential diagnosis
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Image 01 Image 02