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Skin-Melanocytic Tumors
Melanoma in situ
Last major update: November 2008 - next update November 2009
Revised: 26 October 2009
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
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● Malignant melanocytes in epidermis, without dermal invasion
● Variants include lentigo maligna, superficial spreading, and acral melanoma
Clinical
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● Cases in sun damaged skin may resemble benign lichenoid keratosis (Hum Path 2003;34:706)
● Characterized by pagetoid spread, confluence, and nesting of atypical melanocytes
● May be associated with invasive malignant melanoma (Hum Path 2000;31:705)
● Hutchinson's sign: periungual extension of brown-black pigmentation from longitudinal melanonychia [pigmented stripe within length of nail bed] onto the proximal and lateral nailfolds
● Large, pigmented lesions, irregular margins, irregular pigmentation
Case reports
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● Arising within seborrheic keratosis (Cases J 2008;1:263)
● Vitiligo-like in situ disease (Am J Dermatopathol 2008;30:451)
● Involving epidermal inclusion cyst, with adjacent invasive disease (Am J Dermatopathol 2007;29:564)
Treatment and prognosis
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● Excision with negative margins
● Evaluation of entire margin is recommended (Dermatol Surg 2007;33:1434) - not by classic Mohs surgery, slow Mohs may be used
● Imiquimod cream 5% is a nonsurgical alternative (Cutis 2007;79:149)
Clinical images
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Fingernail lesion
Dermoscopy description
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● Blue-whitish veil (78%), gray-blue areas (76%), black dots (73%), irregular extensions and branched streaks (62%) (Cancer 2001;91:992)
● Parallel ridge pattern identifies early acral lesions (Arch Dermatol 2005;141:1413)
Dermoscopic images
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Asymmetric pattern with blue-gray Acral lesion with parallel ridge pattern (Fig B)
globules and focal structureless areas
Micro description
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● Atypical melanocytes in epidermis with no dermal invasion
● Usually epidermal effacement (absences of rete ridges in some foci, J Drugs Dermatol 2007;6:708)
● Predominance of individual unit melanocytes over nests
● Confluent growth of melanocytes along the dermo-epidermal junction
● Pagetoid spread
● Involvement of the adnexal structures
Micro images
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Melanoma in situ With fibrohistiocytic proliferation
extending to epidermis
Hyperkeratotic keratosis with coexisting melanoma in situ MITF staining
Before and after Imiquimod cream Frozen section from Moh’s procedure-
positive and negative margins
Various images Nail bed S100A6 staining (negative)
Videos
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Differential diagnosis
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● Ankle nevi (AJSP 2007;31:1130)
● Seborrheic keratosis with clear basal cells (J Am Acad Dermatol 2006;54:132)
End of Skin-Melanocytic Tumors > Melanoma in situ
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