Morphologic changes in melanocytic nevi induced by exogeneous factors

Malignant melanoma is the most important differential diagnosis in both cli nical and histologic examination of melanocytic nevi. UV exposure with an e rythemagenic dose and mechanical irritation of melanocytic nevi a re able t o 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 af ter 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 p roperties of melanocytes in vitro. Therefore, both keratinocyte-derived fac tors and direct influence of UV on the melanocyte system are probably respo nsible for the morphologic changes. While these exogenously evoked changes are reversible,the potential biologic relevance - especially a possible rol e in the initiation of the carcinogenesis cascade requires clarification.