The significance of Melan-A-positive pagetoid melanocytosis in dysplastic nevi.

Dysplastic nevi may occasionally display alarming histological features. One of these features is the presence of upward spread of melanocytes (pagetoid melanocytosis), identified either on routine histologic sections or after immunohistochemistry using one of the melanocytic markers. Forty-three cases of dysplastic nevi with mild to moderate atypia were selected and retrieved, and Melan-A staining was performed. Melan-A-positive cells with pagetoid architecture were present in 27 cases (63%). Of these, only 5 cases demonstrated pagetoid architecture on routine staining. It is concluded that Melan-A staining should be used only with caution as an adjunct to routine histology in the evaluation of dysplastic nevi with mild to moderate atypia because the identification of pagetoid melanocytosis using this technique has the potential to lead to an erroneous diagnosis of melanoma.