Skin nonmelanocytic tumor
Adnexal tumors
Sweat gland derived (apocrine & eccrine glands)
Myoepithelioma
Author: Christopher S. Hale, M.D.
Last author update: 1 June 2012
Last staff update: 4 March 2025
Copyright: 2002-2025, PathologyOutlines.com, Inc.
PubMed Search: Myoepithelioma
See Also: Soft Tissue - Myoepithelioma
Table of Contents
Definition / general | Gross description | Microscopic (histologic) description | Positive stains | Differential diagnosisCite this page: Hale CS. Myoepithelioma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticmyoepithelioma.html. Accessed March 30th, 2025.
Definition / general
- Tumors with myoepithelial cells but no epithelial cells (Hum Pathol 2004;35:14)
- Usually benign lesions of extremities, but should be completely excised
- May recur locally, rarely metastasize
- Usually male, mean age 22 years (range 10 - 63 years)
- Part of a continuum with mixed tumors (ductal structures but few myoepithelial cells)
- Mitotic activity may predict more aggressive tumor
Gross description
- Mean 1 cm, range 0.5 to 2.5 cm
Microscopic (histologic) description
- Well circumscribed dermal lesions, not connected to epidermis, may extend into superficial subcutis
- Either composed of:
- Solid proliferation of ovoid, spindled, histiocytoid or epithelioid cells with abundant eosinophilic syncytial cytoplasm and little stroma; or
- Reticular architecture with epithelioid, plasmacytoid or spindle cells in myxoid or hyalinized stroma
- Cells have ovoid / spindled nuclei, mild pleomorphism, small necrotic areas, fatty metaplasia, minimal mitotic figures (0 - 6 / 10 HPF), no ductal differentiation
Positive stains
- Required for diagnosis by Fletcher: EMA+ or keratin+, S100, GFAP (50%)
- Muscle markers calponin, smooth muscle actin (57%) or muscle specific actin (HHF)
Differential diagnosis
- Benign mixed tumor
- Cellular neurothekeoma: nested architecture, sclerotic dermal collagen, NKI-C3+, S100-, EMA-, keratin-
- Epithelioid benign fibrous histiocytoma: lower limbs, circumscribed, polypoid, plump and often binucleate epithelioid cells, may entrap dermal collagen, keratin-, myogenic markers-, S100-
- Epithelioid sarcoma: distal extremities of young adults, infiltrates along fibrous septa and fascial planes, discontinuous growth, S100-, GFAP-
- Leiomyoma
- Myoepithelial carcinoma
- Spitz nevus: large epithelioid melanocytes with prominent nucleoli, junctional component, downward maturation, HMB45+, S100+, EMA-, keratin-, myogenic markers-
