Differentiation of proliferative nodules in giant congenital
nevi from
melanoma arising within such
nevi is an important diagnostic challenge. DNA methylation is a well-established epigenetic modification already observed in the earliest stages of
carcinogenesis, which increases during
melanoma progression. The ten-eleven translocation
enzymes catalyze the oxidation of
5-methylcytosine to
5-hydroxymethylcytosine (5-hmC), which has recently been reported as an epigenetic hallmark associated with
tumor aggressiveness and poor prognosis in a wide variety of
cancers. In this study, we analyzed 12 proliferative nodules and 13
melanomas both arising in giant congenital
nevi and matched results with a control group including 67 benign and malignant melanocytic lesions. Proliferative nodules displayed high 5-hmC expression levels (90.65%) compared with
melanomas with almost complete loss of this marker (7.87%). We showed that low 5-hmC levels in
melanomas correlate with downregulation of
isocitrate dehydrogenase and ten-eleven translocation families of
enzymes implicated in the
cytosine methylation cycle. Simultaneously, these
enzymes were overexpressed in proliferative nodules leading to strong 5-hmC expression. We emphasize the significance of 5-hmC loss for discrimination of
melanomas from benign proliferative nodules arising within giant congenital
nevi, and for establishing the correct diagnosis in ambiguous cases when histological and immunohistochemical characteristics are not sufficiently specific.