The value of nucleolar organizer region staining in the differential diagnosis of borderline melanocytic lesions

The technique of silver (Ag) staining of nucleolar organizer region-associated proteins (AgNORs) has been shown to be of value in differentiating between benign and malignant cells. We have studied 33 borderline melanocytic lesions, in which a diagnosis of melanoma had been seriously considered, in order to assess the value of this technique in a commonly encountered diagnostic situation. We found that benign naevus cells possessed single compact or granular AgNORs, whereas some malignant melanocytes possessed large, often loosely arranged groups of AgNORs. However, the pattern of AgNORs observed in melanocytes of some atypical but benign lesions was also seen in some melanomas. The differential diagnosis of borderline melanocytic lesions is not clarified by use of the AgNOR technique.