[Value of nucleolus organizer regions (AgNORs) in dermatologic oncology]

Nucleolus-organizing regions (Ag-NORs) are silver-stained loops of DNA transcribing to ribosomal RNA. Quantitative analysis helps to differentiate normal tissue from malignant tissue and can be used for diagnosis in several kinds of tumours. The analysis of AgNORs can also be used in dermatopathology for diagnostic and prognostic purposes. Apart from skin tumours such as basal, cell carcinomas and squamous cell carcinomas, this technique is of interest principally for melanocytic lesions. Benign naevi can be distinguished from malignant melanomas by simple counting of the AgNOR dots. For the differentiation of dysplastic naevi, Spitz naevi and malignant melanomas, this parameter alone is not sufficient. By combination of several AgNOR parameters (number, size, pattern of dispersal) only, significant differentiation could be achieved. The prognostic value of AgNORs remains to be examined.