Malignant melanoma in giant pigmented nevus
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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; 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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, with a second peak in adult life. Malignant melanoma in giant pigmented nevus carries the risk of metastasis and death
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