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Skin-Melanocytic tumors

Atypical Spitz nevus

Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.

Revised: 26 October 2009, last major update November 2008

Copyright: (c) 2005-2009, PathologyOutlines.com, Inc.

Definition

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Junctional or compound lesion not fulfilling the histopathologic criteria of melanoma but with one of the following features:

● Asymmetry

● Predominance of single melanocytes over nests in lesions 4 mm or larger

● Ulceration

● Large dermal sheets of melanocytes

● Lack of maturation in dermis

● Deep dermal mitotic figures

● Extensive involvement of subcutis

● Nuclear pleomorphism

Terminology

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● Also called Spitz tumor (Mod Path 2006;19 Suppl 2:S21)

Clinical

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● Regional lymph node involvement in up to 1/3 (Hum Path 2006;37:816)

● Usually large and deep with pushing borders into dermis and subcutis

Case reports

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● Resembling dermatofibroma clinically (Clin Exp Dermatol 2008;33:309)

Treatment and prognosis

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● Poor prognostic factors include size > 1 cm, tumor extension into subcutis, ulceration, high mitotic index, older age (Arch Dermatol 1999;135:282, Hum Path 1998;29:1105)

● Borderline biologic behavior between Spitz nevus and malignant melanoma (Mod Path 2005;18:197)

● Complete excision recommended to determine depth and extension; some recommend sentinel node biopsy, particularly if melanoma is suspected (Ann Surg Oncol 2008;15:302, Semin Diagn Pathol 2008;25:95 but see Adv Anat Pathol 2008;15:253)

Micro description

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● Junctional or compound lesion not fulfilling the histopathologic criteria of melanoma but with one of the following features - asymmetry, predominance of single melanocytes over nests in lesions 4 mm or larger, ulceration, large dermal sheets of melanocytes, lack of maturation in dermis, deep dermal mitotic figures, extensive involvement of subcutis, nuclear pleomorphism (Arch Dermatol 2005;141:1381, Cancer 2003;97:499)

Micro images

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AFIP: Large epithelioid cells with amphophilic cytoplasm are                               Various images

characteristic of Spitz nevi, and the nuclear atypia observed

 here should not suggest melanoma in the absence of other features

Asymmetry but highly cohesive                     Slight epidermal hyperplasia and circumscribed,

nests                                                                     wedge-shaped and symmetrical silhouette

Spindle and epithelioid melanocytes do not mature

into dermis and display focal sheet-like growth,

moderate nuclear pleomorphism, and mitotic figures (arrowhead)

Other images: Buttock tumor - somewhat symmetric;  large nests of atypical tumor cells without maturation;  multinucleated tumor cells #1;  #2;  sheets of atypical tumor cells with frequent mitotic figures #1; #2

Positive stains

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● S100, HMB45 only at dermoepidermal junction or superficially

● Mart-1

Molecular / cytogenetics

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● H-RAS occasionally but usually not N-RAS or B-RAF mutations, unlike melanoma (AJSP 2005;29:1145)

● Some cases may have copy number loss of the CDKN2A gene, also seen in melanoma (Br J Dermatol 2007;156:1287)

Differential Diagnoses

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● Spitzoid melanoma

End of Skin-Melanocytic Tumors > Atypical Spitz nevus

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