Breast - nonmalignant
Benign tumors / changes
Myoepithelioma of breast

Author: Hind Nassar, M.D. (see Authors page)

Revised: 9 August 2017, last major update April 2010

Copyright: (c) 2002-2017,, Inc.

PubMed Search: Myoepithelioma [title] breast [title]

Cite this page: Nassar, H. Myoepithelioma of breast. website. Accessed December 13th, 2018.
Definition / general
  • Bland spindle cell lesion with myoepithelial phenotype
  • Rare
Clinical features
  • Usually benign, may recur locally
Case reports
Microscopic (histologic) description
  • Dense spindle cell neoplasm, may be arranged in storiform pattern
  • Tumor cells have eosinophilic cytoplasm, oval and regular nuclei
  • May have polygonal cells with clear cytoplasm and hyperchromatic nuclei
  • May infiltrate fat or surround normal ducts
  • No mitotic figures, no necrosis, no atypia
Microscopic (histologic) images

Images hosted on PathOut server:

Invasive dense spindle cell lesion

Plump interlacing spindle cells with ovoid nuclei


polygonal cells with

Actin+ spindle
cells with positive
internal control in
normal duct at top

Images hosted on other servers:

Broad fascicles

Resembles leiomyoma

Muscle specific actin+

Cytology description
  • Epithelial and spindled cells
  • Mild to moderate nuclear pleomorphism, occasional intranuclear cytoplasmic vacuoles, naked bipolar cells, metachromatic myxoid or fibrillary material
  • No necrosis, no mitotic figures
Positive stains
Negative stains
Electron microscopy description
  • Activated, differentiated myoepithelial cells (cytoplasmic bundles of myofilaments, desmosomes and basal lamina), variable squamous metaplasia (Am J Surg Pathol 1982;6:785)
Differential diagnosis