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Skin - Nonmelanocytic tumors

Adnexal tumors - eccrine sweat glands

Myoepithelioma


Reviewer: Christopher Hale, M.D. (see Reviewers page)
Revised: 4 July 2012, last major update June 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● 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
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● Mean 1 cm, range 0.5 to 2.5 cm

Micro description
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● Well circumscribed dermal lesions, not connected to epidermis, may extend into superficial subcutis
● Either composed of:
(a) solid proliferation of ovoid, spindled, histiocytoid or epithelioid cells with abundant eosinophilic syncytial cytoplasm and little stroma; or
(b) 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

Micro images
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Various images

Positive stains
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Required for diagnosis by Fletcher:
(a) EMA+ or keratin+ and
(b) S100 and
(c) GFAP (50%) or muscle markers calponin, smooth muscle actin (57%) or muscle specific actin (HHF)

Differential diagnosis
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● Myoepithelial carcinoma
● Benign mixed tumor
● Epithelioid benign fibrous histiocytoma: lower limbs, circumscribed, polypoid, plump and often binucleate epithelioid cells, may entrap dermal collagen, keratin-, myogenic markers-, S100-
● Spitz nevus: large epithelioid melanocytes with prominent nucleoli, junctional component, downward maturation, HMB45+, S100+, EMA-, keratin-, myogenic markers-
● Epithelioid sarcoma: distal extremities of young adults, infiltrates along fibrous septa and fascial planes, discontinuous growth, S100-, GFAP-
● Cellular neurothekeoma: nested architecture, sclerotic dermal collagen, NKI-C3+, S100-, EMA-, keratin-
● Leiomyoma

End of Skin - Nonmelanocytic tumors > Adnexal tumors - eccrine sweat glands > Myoepithelioma


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