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Skin-Melanocytic Tumors
Pigmented epithelioid melanocytoma
Last major update: November 2008 - next update November 2009
Revised: 22 September 2009
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
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● Controversial entity, encompassing epithelioid blue nevus and pigment synthesizing melanoma (animal type, equine type melanoma) characterized by prominent pigment synthesis
Clinical
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● Rare low grade variant of melanoma, first described under this name in 2004 (AJSP 2004;28:31)
● Mimics melanocytic neoplasms in gray horses and laboratory animals, although appears to have different molecular origin than equine melanomas (AJSP 2004;28:31)
● Includes lesions previously described as epithelioid blue nevus of the Carney complex (AJSP 2004;28:31)
● Median age 27 years, with wide range
● Extremities are most common site, although numerous sites are affected
● Does not appear to be related to sun exposure
● Nodal metastases in 46%, but death from disease is rare
Case reports
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● 27 year old man with sentinel node metastasis and balloon cell change (Am J Dermatopathol 2001;23:341)
● 28 year old woman with positive sentinel node biopsy (Am J Dermatopathol 2004;26:290)
● Subungual tumor with blue nevus (J Am Acad Dermatol 2008;58:1021)
Treatment and prognosis
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● Conservative re-excision and sentinel lymph node sampling
Clinical description
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● Resembles combined nevus
Clinical images
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Micro description
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● Sheets and nodules of heavily pigmented epithelioid or spindled melanocytes in deep dermis
● Variable atypia but no consistent high grade features
● May have ulceration, a combined nevus or rarely necrosis
● After bleaching, cells have abundant gray, slate-like cytoplasm, round nuclei, prominent nuclear membrane, prominent nucleoli
● Rarely 2 nucleoli or cytoplasmic inclusions
● No/rare mitotic figures, no atypia
Micro images
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Melanocytoma
Case of the week #113
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Positive stains
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● S100, MiTF, NKI/C3, NSE, p53, CD68
Negative stains
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● HMB45, MelanA, R1alpha (AJSP 2007;31:1764)
Electron microscopy
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● Abundant cytoplasm with numerous single and rare compound melanosomes
● Frequent aberrant melanosomes
● Large indented nucleus with prominent nuclear membrane, central nucleolus, peripheral chromatin
Molecular / cytogenetics
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● Associated with loss of protein kinase A regulatory subunit type 1alpha (R1alpha), coded by the PRKAR1A gene, which is lost in both sporadic cases and patients with Carney complex (AJSP 2007;31:1764)
Differential diagnosis
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● Blue nevus - no pigmented and epithelioid cells
● Nodular melanosis - pigmented cells are actually pigment laden macrophages
End of Skin-Melanocytic Tumors > Pigmented epithelioid melanocytoma
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