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WHO Classification of Tumours
Lentigo maligna
Skin


Definition

Lentigo maligna (LM) is a form of melanoma , histologically characterized by a proliferation of atypical melanocytes in the dermal-epidermal junction and down the walls of hair follicles and sweat ducts, without infiltration of the papillary or reticular dermis. The atypical melanocytes show marked pleomorphism. Typical is the presence of a lymphocytic infiltrate and of focal fibroplasia in the papillary dermis underlying the lesion. The melanocytic proliferation is associated with actinic damage and epidermal atrophy. Regression is common.
Macroscopically, the typical LM is a broad, flat zone of varied pigmentation with an irregular border. With increasing size of the lesion, nodules may develop within the lesion and the borders may become difficult or impossible to define. The most frequently affected sites are head and neck.
Lentigo maligna typically develops on the sun-exposed skin of elderly people, suggesting that it arises in response to chronic, accumulated sun exposure, in contrast to other types of melanoma which appear to be related to high intensity intermittent sun exposure. Complete excision of lentigo maligna is curative. The prognosis is generally better than for other types of melanomas, reflecting the differences in tumour thickness

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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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When the lesion invades the dermis, the term lentigo maligna melanoma (LMM) is used.