The new england journal of medicine n engl j med 374;10 nejm.org March 10, 2016 994 To the Editor: In their study, Shain et al. inves- tigated the genetic evolution of melanoma from presumed precursor lesions and evaluated mor- phologically intermediate lesions, which have a higher mutational burden than do benign lesions. The authors suggest that these intermediate le- sions have previously been termed “dysplastic” (citing dysplastic nevi as the example), but most dysplastic nevi are stable and never progress. 1 More robust linkage between melanomas and potential precursors may involve fields of atypi- cal junctional melanocytes that occur in chroni- cally sun-damaged skin and frequently surround fully excised melanomas. The melanocytes form- ing these fields do not qualify histologically for a designation of melanoma, but we have found them to be defective in the level of the epigenetic mark 5-hydroxymethylcytosine (Fig. 1), and this defect has been shown to correlate functionally with melanoma growth (in an in vivo model) 2 and with features of melanocytic dysplasia. 3 Fields of atypical melanocytes are also relevant to previous research by Bastian et al., in which occult cells harboring genetic amplifications were identified in the epidermis adjacent to acral melanomas. 4 Future studies that seek to define intermediate lesions as potential melanoma precursors should focus on both epigenetic and genetic analyses of such proliferations. Christine G. Lian, M.D. George F. Murphy, M.D. Brigham and Women’s Hospital Boston, MA No potential conflict of interest relevant to this letter was re- ported. Figure 1. Atypical Skin Melanocytes with Loss of Epigenetic Mark 5-Hydroxymethylcytosine. Panel A shows hematoxylin and eosin staining of a field in which melanoma arose; hyperplasia of cytologically atypical melanocytes is visible (arrows). Panel B shows dual-label immunofluorescence staining of a sample of human skin that contains cytologically normal melanocytes (left), which are positive for MART-1 (melanoma-associated antigen recognized by T cells; green) and have uniform stain- ing for nuclear 5-hydroxymethylcytosine (red); a sample of human skin with long-term exposure to ultraviolet light (right) shows loss of 5-hydroxymethylcytosine, a finding that is characteristic of atypical melanocytes. The insets show the samples at high magnification. Panel C shows dual-label immunohistochemical staining of a sample of human skin that contains cytologically normal melanocytes, which are positive for MART-1 (blue) and have uniform, strong staining for nuclear 5-hydroxymethylcytosine (brown), whereas Panels D and E show adjacent enlarged, atypical melanocytes (arrows) that have partial loss (Panel D) or complete loss (Panel E) of 5-hydroxy- methylcytosine. A C D E B The New England Journal of Medicine Downloaded from nejm.org at DFCI on March 10, 2016. For personal use only. No other uses without permission. Copyright © 2016 Massachusetts Medical Society. All rights reserved.