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Breast-nonmalignant
Benign tumors / changes
Myoepithelioma of breast
Reviewer: Hind Nassar, M.D. in January 2009 (see Authors page)
Revised: 14 April 2010, last major update April 2010
Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.
Definition
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● Bland spindle cell lesion with myoepithelial phenotype
Terminology
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● Myoepitheliosis: multifocal, often microscopic proliferation of myoepithelial cells in or around small ducts; usually an incidental finding and not palpable (Am J Surg Pathol 1991;15:554)
● See also myoepithelial carcinoma in Breast-Malignant chapter
Epidemiology
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● Rare
Sites
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Etiology
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Clinical features
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● Usually benign, may recur locally
Prognostic factors
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Case reports
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● 71 year old woman with local recurrence (Tunis Med 2004;82:324)
● Renal dialysis patient with benign appearing tumor with metastatic behavior (ANZ J Surg 2004;74:1135)
Treatment
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Clinical images
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Gross description (Macroscopy)
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Gross images
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Micro description (Histopathology)
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● 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
Micro images
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Invasive dense Plump interlacing spindle Occasional polygonal cells
spindle cell lesion cells with ovoid nuclei with hyperchromatic nuclei
Broad fascicles Resembles leiomyoma
Actin+ spindle cells with Muscle specific actin+
positive internal control
in normal duct at top
Virtual Slides
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Videos
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Cytology description
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● 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
Cytology images
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Positive stains
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● Myoepithelial cell phenotype: keratin, EMA, alpha smooth muscle actin, calponin, caldesmon, vimentin, CD10, p63, S100
Negative stains
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● Low molecular weight keratin CK8/18 (CAM5.2), desmin, CD34, ER, PR
Electron microscopy descriptions
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● Activated, differentiated myoepithelial cells (cytoplasmic bundles of myofilaments, desmosomes and basal lamina), variable squamous metaplasia (Am J Surg Pathol 1982;6:785)
Electron microscopy images
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Molecular / cytogenetics description
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Molecular / cytogenetics images
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Differential Diagnosis
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● Adenomyoepithelioma: also epithelial cells
● Metaplastic carcinoma: has malignant component
● Myoepithelial carcinoma: has malignant cells and mitotic activity
● Myofibroblastoma: lacks epithelial phenotype (keratin-, S100-)
Additional references
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End of Breast-nonmalignant > Benign tumors / changes > Myoepithelioma
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