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[Morphological changes in melanocytic nevi induced by exogenous factors].

Malignant melanoma is the most important differential diagnosis in both clinical and histologic examination of melanocytic nevi. UV exposure with an erythemogenic dose and mechanical irritation of melanocytic nevi are able to induce reversible morphologic changes which simulate malignant melanoma. These changes are associated with an increased expression of HMB-45 antigen. In addition, an increased proliferation and repair activity is observed after UV exposure. The increased number of melanocytes located in suprabasal layers of the epidermis is accompanied by a change in keratinocyte adhesion molecule expression. The UV light is also able to influence the adhesive properties of melanocytes in vitro. Therefore, both keratinocyte-derived factors and direct influence of UV on the melanocyte system are probably responsible for the morphologic changes. While these exogenously evoked changes are reversible, the potential biologic relevance--especially a possible role in the initiation of the carcinogenesis cascade--requires clarification.