Subungual pigmented nevus: evaluation of DNA ploidy in six cases.

The discrimination between subungual pigmented nevus and subungual melanoma in situ is still a clinical problem. We measured DNA ploidy in six cases of subungual melanotic lesions which exhibited the features of subungual pigmented nevus or lentigo simplex histologically. Five cases presented a diploid pattern with or without a slight increase of hyperdiploid cells. One case presented a polyploid pattern; it also exhibited histologically abnormal melanocytes with large nuclei and pigment-filled elongated dendrites. The DNA ploidy pattern and histologic features suggest that the lesion of this latter case contains abnormal melanocytes which probably have the potential to undergo a malignant transformation into a subungual melanoma. DNA ploidy analysis, therefore, is likely to provide information for evaluating the biologic behavior of subungual melanotic lesions.