Definition
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
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
Original posting:: May 15, 2006
Supplemental studies
Immunohistology
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
Histochemistry
PAS stain demonstrates glycogen in myoepithelial cells
Differential Diagnosis
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
Papilloma with Prominent Myoepithelial Cells
Adenomyoepithelioma
Myoepithelial cells restricted to basal layer on papillae
Prominent, expanded myoepithelial component forming nodules or nests
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
Clinical
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
Lists
Breast Tumors and Lesions Exhibiting Reactivity for Muscle/Myoepithelial Markers
(Most benign lesions with an epithelial component will have a myoepithelial cell layer)
Bibliography
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.
