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Surgical Pathology Criteria

Adenomyoepithelioma of the Breast


  • Biphasic epithelial/myoepithelial breast neoplasm with a clear expansion of the myoepithelial component

Diagnostic Criteria

  • Biphasic with prominent myoepithelial component
    • Tubules lined by cuboidal to columnar epithelial cells
      • Frequent apocrine differentiation
      • May be pushed to edge of nodule
      • May be compressed, resembling multinucleated giant cells
    • Prominent, expanded myoepithelial component
      • Usually polygonal with clear cytoplasm
        • May be spindled
      • Range from evenly distributed to focal nests/nodules to predominant
        • 95% of cases >25% myoepithelial
        • 84% of cases >50% myoepithelial
      • Positive staining for glycogen, keratin and muscle markers
    • Both components cytologically bland
      • Minimal pleomorphism
      • Low mitotic rate
  • Circumscribed lesion
    • Lobulated, multinodular or papillary
    • Pushing border but not infiltrating
  • Occasional findings
    • Basophilic background stroma
    • Central necrosis and dystrophic calcification
    • Focal fibromatosis-like myofibroblastic response
      • May contain rare keratin positive cells
      • No clinical significance
  • In the literature, the term adenomyoepithelioma has been applied loosely to a variety of lesions
    • If cytologically atypical or invasive, diagnose instead as appropriate type of carcinoma, sarcoma or malignant myoepithelial neoplasm
    • Any other lesion present should be diagnosed separately as such
    • Criteria above derived largely from McLaren 2005
  • Identical in appearance to epithelial-myoepithelial carcinoma of salivary gland

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: May 15, 2006

Supplemental studies



Epithelial Cells

Myoepithelial Cells

Keratin Positive Variable
EMA Positive Positive, variable
p63 Negative Positive
Calponin Negative Positive, variable
Smooth muscle actin Negative Positive, variable
Muscle specific actin Negative Positive, variable
Desmin Negative Positive, variable
CD10 Negative Positive, variable
GFAP Negative Positive, variable
S100 Negative Positive, variable



  • PAS stain demonstrates glycogen in myoepithelial cells

Differential Diagnosis


Various processes may have prominent atypical myoepithelial cells

  • Cytologic atypia, increased mitotic rate, stromal invasion are not permitted in adenomyoepithelioma
  • Such cases should be diagnosed based on the malignant component present
  • Some such cases have been designated as "solid pattern adenomyoepithelioma" (Tavassoli 1991)
    • We do not use that terminology


Adenomyoepithelioma Myoid Hamartoma
Myoepithelial component positive for keratin, p63, smooth muscle actin Myoid component positive only for smooth muscle actin
Tubules without lobules Well formed ducts and lobules
No admixed fat Admixed fat


Pleomorphic Adenoma Adenomyoepithelioma
Chondromyxoid stroma Lacks chondromyxoid stroma
Otherwise the lesions may be identical


Low Grade Adenosquamous Carcinoma Adenomyoepithelioma
Squamous differentiation frequent Squamous differentiation not described
Infiltrative pattern Circumscribed, not infiltrative
Otherwise the lesions may be identical


Papilloma with Prominent Myoepithelial Cells Adenomyoepithelioma
Myoepithelial cells restricted to basal layer on papillae Prominent, expanded myoepithelial component forming nodules or nests


Ductal Adenoma Adenomyoepithelioma
Hyalinized stroma Cellular stroma
Circumscribed, encapsulated Capsule unusual
Ductal adenoma may have myoepithelial overgrowth


Metaplastic Carcinoma Adenomyoepithelioma
Glandular component, if present, is histologically malignant, except in low grade spindle cell metaplastic carcinoma Epithelial component is histologically bland
Stromal component may be bland or histologically malignant Stroma is histologically bland
Stromal component may resemble a variety of sarcomas or low grade fibrous proliferation Stroma shows myoepithelial differentiation only
Squamous differentiation may be present No squamous differentiation


Myofibroblastoma Adenomyoepithelioma
No epithelial component Tubules integral to lesion
Stromal keratin negative, CD34 positive, muscle/myoid markers variable Stromal keratin variable, p63 and muscle/myoid markers positive


  • Age 22-92 years
  • Size 0.3-7 cm
  • May recur if incompletely excised
  • No aggressive recurrrences or metastases, as long as the lesion is mitotically inactive and histologically bland

Grading / Staging

  • Grading and staging are not applicable


Breast Tumors and Lesions Exhibiting Reactivity for Muscle/Myoepithelial Markers

(Most benign lesions with an epithelial component will have a myoepithelial cell layer)


  • McLaren BK, Smith J, Schuyler PA, Dupont WD, Page DL. Adenomyoepithelioma: clinical, histologic, and immunohistologic evaluation of a series of related lesions. Am J Surg Pathol. 2005 Oct;29(10):1294-9.
  • Tavassoli FA. Myoepithelial lesions of the breast. Myoepitheliosis, adenomyoepithelioma, and myoepithelial carcinoma. Am J Surg Pathol. 1991 Jun;15(6):554-68.
  • Rosen PP. Adenomyoepithelioma of the breast. Hum Pathol. 1987 Dec;18(12):1232-7.
  • Popnikolov NK, Ayala AG, Graves K, Gatalica Z. Benign myoepithelial tumors of the breast have immunophenotypic characteristics similar to metaplastic matrix-producing and spindle cell carcinomas. Am J Clin Pathol. 2003 Aug;120(2):161-7.

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