HLA antigen expression in melanocytic lesions: Is acquisition of HLA antigen expression a biomarker of atypical (dysplastic) melanocytes?

Background Although criteria are established for the histologic diagnosis of atypical nevi (AN), consensus about the criteria in the diagnosis of and in the definition of AN is limited. Moreover, intraobserver and interobserver differences in the application of these criteria for the diagnosis of AN have been observed. Objective We sought to determine the usefulness of HLA antigen expression as a biomarker of AN. Methods The immunoperoxidase reaction was used to mark common nevi and AN with HLA class I heavy chain–, β2microglobulin (β2m)-, and HLA class II β chain–specific monoclonal antibodies. Results HLA class I heavy chain, β2m, and HLA class II β chain were expressed in 5 (8.6%) of the 58 common nevi and in 46 (∼72%) of the 64 atypical melanocytic lesions. Among common lesions, only halo nevi expressed HLA class I heavy chain, β2m, and HLA class II β chain. The level of HLA class I heavy chain β2m and of HLA class II β chain expression correlated with the degree of cytologic atypia and architectural disorder. Limitations The number of lesions tested and the subjective nature of the analysis of immunohistochemical staining of tissue sections are both limitations. Conclusions The data presented suggest that HLA antigen expression is an objective biomarker that correlates well with the degree of cytologic atypia in AN and may: (1) be useful to distinguish common nevi from AN, and (2) represent a more objective measure to determine which AN should be excised.