A distinctive melanocytic lesion associated with melanoma-prone dysplasticnaevus syndrome: the hybrid naevus

Clinically and histologically, the concept of dysplastic nevi remains contr oversial. To elaborate more precise criteria for the nevi of patients with dysplastic naevus syndrome (DNS), we examined 58 nevi from seven DNS patien ts who developed one or several malignant melanomas. Clinical presentation and histomorphology were evaluated, and immunohistochemistry was performed using proliferation marker Ki-SS and antibody DO-7 to the p53 protein. Sixt y nevi from individuals without history of melanoma served as controls. Of the DNS nevi, 21 (36.2%) exhibited no morphological particularities. The re maining 37 nevi presented distinctive histological features consisting of a slight epidermal acanthosis, spitzoid vertically oriented nests of dyscohe sive nevus cells, and single-standing atypical melanocytes in the basal cel l layer of the epidermis. Immunohistochemical analysis revealed an average proliferation index of 2.5%, which significantly surpassed the mean growth fraction of conventional dysplastic nevi (<1%). No increase in p53 expressi on was observed. Characteristically, active proliferation was found in junc tional single-standing melanocytes with or without nuclear atypia rather th an in nest-shaped compounds. In conclusion, certain moles of patients with DNS possess distinctive features. The newly characterized criteria may prov ide a basis for the diagnosis of DNS and might help to identify patients at increased risk for malignant melanoma by examination of a single biopsy.