CLONALITY IN NEVOCELLULAR NEVUS AND MELANOMA - AN EXPRESSION-BASED CLONALITY ANALYSIS AT THE X-LINKED GENES BY POLYMERASE CHAIN-REACTION

The true nature of nevocellular nevus is still unknown and it has been ambiguously classified as a neoplasm or a hamartoma. We studied the c lonality of nevocellular nevus and melanoma (malignant melanoma), usin g an expression-based clonality analysis at the X-linked genes by mean s of polymerase chain reaction. DNA was extracted from cryostat sectio ns of 20 nevocellular nevi (10 compound and 10 intradermal type) and f ive melanomas from female patients. A polymorphic portion of the inact ivated X-Linked gene was amplified after selective digestion of the ac tive X-chromosome with a methylation-sensitive restriction enzyme, Hpa II. Paternal-and maternal-derived fragments were resolved with electr ophoresis using the polymorphic restriction endonuclease (BstX I) site for the phosphoglycerate kinase assay, and using the difference of CA G repeats for the human androgen-receptor gene assay. Both assays reve aled that all informative nevocellular nevi were polyclonal in origin and all melanomas were monoclonal, Results of the clonality were indep endent of either the histologic type of nevocellular nevus or whether the nevocellular nevus was of congenital or acquired origin. Thus, nev ocellular nevus, congenital or acquired, may be a hamartomatous rather than a neoplastic lesion. The analysis of clonality could be applied to the differential diagnosis of benign melanocytic disease and melano mas.