The epidermal melanin unit in the pathophysiology of malignant melanoma.

The epidermal melanin unit (EMU) denotes the symbiotic relationship between a melanocyte and a pool of associated keratinocytes. We propose to show that alterations in the biology of the EMU are the main determinant of the different patterns of intraepidermal growth of melanocytes in lentigo maligna melanoma (LMM) and superficial spreading melanoma (SSM). They also appear to affect the biosynthesis of melanin and melanosomes during malignant transformation. Findings in histochemical studies with monoclonal antibodies generated against melanosomal proteins to produce different stains of melanocytes of normal skin, dysplastic melanocytic nevi (DMN), common melanocytic nevi (CMN), LMM, and SSM have led to the suggestion that the altered melanosome synthesis is a main phenotype in the pathophysiology in neoplastic transformation of melanocytes. Altered melanin synthesis may also affect the carcinogenesis in malignant melanoma: pheomelanin is increased in malignant melanoma and DMN, but not in normal skin and CMN. Pheomelanin and its precursors could aid the malignant transformation of melanocytes through the generation of mutagenic ultraviolet photoproducts in familial DMN syndrome.