5-Hydroxymethylcytosine Expression in Proliferative Nodules Arising within Congenital Nevi Allows Differentiation from Malignant Melanoma

Abstract

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.

Paediatric melanoma

“…Immunohistochemistry can be useful demonstrating immunohistochemical expression levels of Ki‐67 and PHHH3 in histologically benign and atypical proliferative nodules in CN . Recently, Pavlova et al emphasized the role of 5‐hydroxymethylcytosine (5‐hmC) in the differentiation of proliferative nodules from melanoma, as they demonstrated a high 5‐hmC expression (90.65%) in PN and a low or absent (7.8%) expression in melanomas.…”

Molecular Testing for Cutaneous Melanoma: An Update and Review

“…46,47 Loss of 5-hmC has been shown to be a diagnostic hallmark of malignant melanoma and to distinguish among a spectrum of histologic and genetically distinct subtypes of melanoma and benign nevi with high sensitivity and specificity. [48][49][50][51][52][53] In general, benign melanocytic proliferations demonstrate strong nuclear reactivity for 5-hmC, whereas those with increasing malignant potential demonstrate increasing loss of 5-hmC, a finding that has been reproducibly observed in a number of independent studies. In the most recent and largest independent validation study to date, Saldanha et al 54 demonstrated that 5-hmC loss was, after controlling for existing staging and prognostic pathologic parameters, independently associated with worse prognosis and that the assay was easily and reproducibly performed.…”

“…54 A recent study also demonstrated its ability to consistently distinguish malignant melanomas from benign proliferative nodules arising within precursor giant congenital melanocytic nevi. 51 Unlike the assays discussed above that require macro/ microdissection of tumoral melanocytes, which are left vulnerable to inclusion of nuclei from benign precursor nevus cells, epidermal keratinocytes, or stromal/connective tissue cells, this immunohistochemistry-based assay for 5hydroxmethylcytosine enables evaluation at a molecular level of each individual cell of interest within the context of an entire histologic section (Figure 2, A through C). To this end, we have also demonstrated that this epigenetic biomarker may facilitate (1) microstaging and Breslow depth assessment of vertical growth phase melanomas associated with either small cell change, pseudomaturation, or preexisting nevus at the deepest aspect of the tumor 55 ; (2) risk assessment of heavily pigmented, histologically ambiguous, and malignant melanocytic tumors, including atypical deep penetrating nevi, pigmented epithelioid melanocyto- Figure 2.…”

Melanoma: Genetic Abnormalities, Tumor Progression, Clonal Evolution and Tumor Initiating Cells

“…Importantly, the expression of active TET2 or IDH2 into melanoma cells restores the 5-hmC landscape, inhibits melanoma proliferation, and increases survival in animal models [ 83 ]. The association between the loss of 5-hmC levels and malignant melanoma transformation was also supported through the study of proliferative nodules arising with congenital nevi; these nodules display some atypical features and predispose to malignant transformation, but were basically benign and exhibit—in contrast to melanomas—high 5-hmC levels and high TET2 and IDH2 activity [ 161 ]. TET2 and TET3 are silenced in melanoma cells by epigenetic mechanisms triggered by TGF-β and mediated by DNA methyltransferase 3A (DNMT3A); these events play a functional role in the epithelial-to-mesenchymal transition (EMT) and in metastatic processes of melanomas [ 162 ].…”