Assessment of clonality in melanocytic nevi

Background: Melanocytic nevi are among the most common lesions in man; however; their pathogenesis remains largely unknown. While often held to be neoplastic, this hypothesis has not been conclusively verified. Alternatively, some authorities have held that melanocytic nevi are hamartomas. More practically, difficulty may be encountered in the histologic discrimination of melanocytic nevi from melanoma. It was reported that nevi may be differentiated form melanoma in females by polymerase chain reaction (PCR) analysis of loci of human androgen receptor gene on the X-chromosome. However, contradictory findings have also been reported, suggesting that both acquired nevi and melanoma are clonal. Methods: Fifteen examples of melanocytic nevus were analyzed via PCR for pattern of X-chromosome inactivation as indicated by the methylation status of the human androgen receptor gene. Results: Among 15 nevi analyzed, 11 cases provided informative polymorphism at the androgen receptor loci. Nine of these 11 cases revealed a non-random pattern of X-chromosome inactivation. Conclusions: These findings suggest that melanocytic nevi are clonal/neoplastic lesions. As such, they cannot be discriminated from melanoma on the basis of clonality.