[AgNOR expression in skin tumors. Studies of melanocytic, epidermal and fibrohistiocytic lesions].

Nucleolus organizer regions are segments of DNA-coding ribosomal genes, which can be visualized histologically by a special silver staining technique as so-called AgNORs. Determination of the number and size of AgNORs provides quite a precise reflection of current cellular proliferation activity. We have examined the AgNOR expression in 228 melanocytic, epidermal and fibrohistiocytic lesions. Dysplastic naevi and Spitz naevi showed a significantly lower AgNOR expression than melanomas, and there were analogous differences between keratoacanthomas and carcinomas. Furthermore, there were also significant differences between the groups of melanomas and carcinomas, as there were between benign and non-benign fibrohistiocytic lesions. The AgNOR expression in more cellular fibrohistiocytic lesions differed from at in more fibrous lesions. Analysis of AgNOR areas was not so informative as AgNOR counting. The results of PCNA examinations correlated with the degree of AgNOR expression. It was found that the AgNOR technique is useful in differential diagnosis and for histological determinations of proliferation activity in melanocytic, epidermal and fibrohistiocytic lesions. The AgNOR method is easy to apply and can be applied in paraffin-embedded tissue.