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Benign (usually) tumors / tumor like-changes



Reviewer: Hind Nassar, M.D., Johns Hopkins Medical Centers (see Reviewers page)

Revised: 3 October 2012, last major update July 2010

Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.




● Tumor composed of variable number of myoepithelial cells around small epithelial lined spaces

● First recognized in the breast by Hamperl (Curr Top Pathol 1970;53:161)




Other breast myoepithelial lesions are myoepitheliosis and myoepithelioma

● The terminology "adenomyoepithelial adenosis" is no longer used

Page recommends that cases with malignant histology not be called adenomyoepithelioma but be defined by the histology of the malignant component (Am J Surg Pathol 2005;29:1294)




● Uncommon, mean age 60 years

● Rare in male breast




● Usually occurs in the peripheral portion of the breast, but can be central

● No predilection for either breast




● Considered a variant of intraductal papilloma


Clinical features


● Usually presents as a mass

● Usually benign, although may recur locally

● Benign appearing tumors rarely metastasize to lung (Arch Pathol Lab Med 2006;130:1349)

Malignant tumors are usually low grade; may metastasize to lung, brain, jaws, lymph nodes


Prognostic factors


● Mitotic rate > 3 MF/10 HPF is associated with recurrence

● High mitotic rate, atypia, necrosis and infiltrative borders favor malignancy


Case reports


● Cellular tumor (Am J Surg Pathol 1983;7:863)

● 48 year old woman with tumor containing collagenous spherulosis (J Clin Path 2004;57:83)

● 56 year old woman with intracystic tumor (Breast Cancer 2007;14:429)


Malignant tumors

● Benign tumor recurring as malignant myoepithelioma (J Med Imaging Radiat Oncol 2009;53:234)

● 50 year old woman with tumor transforming to osteosarcoma and carcinoma and causing death (Am J Surg Pathol 1998;22:631)

69 year old woman with malignant myoepithelial component and p53 mutation (Pathol Int 2006;56:211)

● 71 year old woman (Arch Pathol Lab Med 2000;124:632)

● 75 year old woman (Arch Pathol Lab Med 2004;128:235)

● 77 year old woman whose tumor had matrix production (Pathol Res Pract 2007;203:599)

80 year old woman (Eur J Gynaecol Oncol 2009;30:234)




● Complete local excision

● May recur with incomplete excision


Gross description (Macroscopy)


● Well circumscribed, usually small (mean 1-2 cm), but can be up to 8 cm

● Firm

● May have satellite nodules


Gross images




Unusually large bisected tumor with central              Intracystic nodule             

cavity with bosselated contour (AFIP)


Micro description (Histopathology)


● Well circumscribed, may be encapsulated or multinodular

● Proliferation of epithelial and myoepithelial cells

● Aggregated lobules of glands with tall lining epithelium with scant cytoplasm and hyperchromatic nuclei surrounded by myoepithelial cells with clear cytoplasm

● Epithelial cells usually form glandular spaces

● Myoepithelial cells can be dominant and may be spindle-shaped, clear or polygonal

● Apocrine metaplasia may be present, also adenomyoepitheliomatous hyperplasia

● Variants include spindle cell type (epithelial-lined spaces may be sparse, resembles leiomyoma), tubular variant (ill-defined margins, may resemble tubular adenoma), lobulated variant (nests of myoepithelial cells surround compressed epithelial lined spaces)

● Malignant appearing cases have local invasion, high mitotic rate, severe atypia (Am J Surg Pathol 1992;16:868)


Micro images




Proliferation of epithelial and myoepithelial cells


Myoepithelial cells are difficult to identify                    Various images and stains

With collagenous spherulosis



AFIP images:


Intraductal bands of pale myoepithelium                     Myoepithelial cells with clear cytoplasm crowd

separate adenomatous ductal epithelium                   glandular epithelium and expand into stroma 




Overgrowth of myoepithelium in two nodules            Myoepithelial cells in small clusters

separated by stromal band                                             have replaced most ductal elements




Foci of glands with luminal secretions                         Isolated myoepithelial cells with

clear vacuolated cytoplasm



Transition between adenomatous and myomatous growth




AE1+ glandular cells, (myoepithelial                             Myoepithelial cells are focally actin+

cells are negative




Epithelial cells are CK7+                                                   Myoepithelial cells are CK5/6+



Benign histology but malignant behavior


Benign appearing tumors that                                        Lung metastases with benign histology

metastasized to lung



Malignant histology


Mitotic activity                     Various images                                                  Keratin+ epithelium



Fig A: biphasic growth with dark areas of hyperchromatic cells with high N/C ratio and pale zone of large polygonal pale cells with ill-defined cytoplasm and vesicular nuclei

Fig B: mitotic figure (arrow)

Fig C: AE1-AE3 staining of epithelial component

Fig D: S100 staining of myoepithelial component


Cytology description


● Moderate to highly cellular with large clusters of epithelium and myoepithelium

● Tubular structures occasionally found

● Myoepithelium appears as small clusters or dispersed cells with epithelioid morphology, intranuclear or intracytoplasmic vacuoles, often naked bipolar nuclei

● Mild to moderate nuclear atypia present

● Metachromatic fibrillary stroma occasionally found

● No mitotic figures, no necrosis

● Often classified incorrectly as fibroadenoma, suspicious for malignancy or malignant (Cancer 2006;108:250)


Cytology images



Various images

Virtual Slides



Benign tumor with case report


Positive stains


Epithelial component:

● keratin (AE1-AE3), CEA; variable ER


Myoepithelial component:

● p63 (AJSP 2001;25:1054), S100, smooth muscle myosin heavy chain


Negative stains


● PR


Electron microscopy descriptions


● Myoepithelial features (classic) include myofibrils with dense bodies, pinocytotic vesicles, desmosomes or tight junctions, patchy basement membrane


Molecular / cytogenetics description


● Case report with t(8;16)(p23;q21) (Cancer Genet Cytogenet 2005;156:14)


Differential Diagnosis


Adenosis tumor: no prominent myoepithelial component

Intraductal papilloma: no prominent myoepithelial component

Invasive carcinoma (on core biopsy): unequivocal evidence of invasion

Nipple adenoma: no prominent myoepithelial component

Tubular adenoma: very well circumscribed (tubular variant is not), myoepithelial cells are inconspicuous or rare


Additional references


Hum Path 1987;18:1232, Stanford University


End of Breast-nonmalignant > Benign tumors / changes > Adenomyoepithelioma



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