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WHO Classification of Tumours
Melanoma, NOS
Skin


Definition

Malignant melanoma is a malignant, usually aggressive tumour histologically composed of atypical, neoplastic melanocytes. Cutaneous melanomas may arise from acquired or congenital melanocytic or dysplastic nevi. They develop most frequently on the face; other commonly affected sites include ears, head, neck, back and shoulders in male patients and the lower limbs in females. Most lesions show an initial radial growth phase within the epidermis and superficial dermis, followed by a vertical growth phase which results in the formation of papules or nodules and eventually involves the subcutaneous tissue
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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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Approximately 80% of melanoma patients are light-skinned Caucasians. The most important environmental risk factor is intermittent exposure to UV radiation, especially during childhood. Familial/genetic risk factors include skin type, number of nevi, the presence of dysplastic nevi, and a family history of melanoma. The single most important prognostic factor is vertical tumour thickness; lesions that have entered the vertical growth phase have metastatic potential and a poor prognosis. Usually, melanomas first metastasize to the regional lymph nodes. Distant metastases arise preferentially in skin, lungs, liver, central nervous system and bones, but any organ may be affected. Survival has increased substantially over the last three decades, mainly due to early detection

Click for details
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



.

Four major subtypes of malignant melanoma are distinguished:
Superficial spreading melanoma
Nodular melanoma
Acral lentiginous melanoma
Lentigo maligna melanoma