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WHO Classification of Tumours
Malignant melanoma in giant pigmented nevus
Skin


Definition

This melanoma subtype arises in a giant congenital nevus (GCN)which is consideresd a direct precursor lesion. The malignant melanoma in giant pigmented nevus usually presents as a rather rapidly growing, asymmetrical nodule or plaque and is sharply demarcated from the surrounding congenital nevus. On the surface, the epidermal rete ridges are effaced, and ulceration is common.
Histologically, the intraepidermal component is usually composed of pigmented epithelioid cells with pagetoid spread. The tumour cells of the dermal component typically form expansile nodules and exhibit fully transformed malignant characteristics with very irregular chromatin patterns and prominent nucleoli.
The incidence of giant congenital nevus is estimated as 1 per 20,000 infants

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Alper J, Holmes LB, Mihm MC (1979)
Birthmarks with serious medical significance: nevocullular nevi, sebaceous nevi, and multiple café au lait spots.
J Pediatr 95: 696-700




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Kopf AW, Bart RS, Hennessey P (1979)
Congenital nevocytic nevi and malignant melanomas.
J Am Acad Dermatol 1: 123-30



; recent studies suggest a risk of malignant transformation of around 6% patients. The frequency of melanoma development is high before the age of 10
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Marghoob AA (2002)
Congenital melanocytic nevi. Evaluation and management.
Dermatol Clin 20: 607-16, viii



, with a second peak in adult life. Malignant melanoma in giant pigmented nevus carries the risk of metastasis and death
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LeBoit PE, Burg G, Weedon D, Sarasin A (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Skin Tumours
3rd Edition
IARC Press: Lyon 2005



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