BRAF V600E expression in juvenile xanthogranuloma occurring after Langerhans cell histiocytosis.

Histiocytoses are a heterogeneous group of diseases resulting from the abnormal proliferation of cells derived from macrophages or monocytes, or dendritic cells at various sites, including bones, soft tissues and skin. Histiocytosis comprises the Langerhans group (L group), including Langerhans cell histiocytosis (LCH); cutaneous and mucocutaneous histiocytosis (C group), comprising juvenile xanthogranuloma (JXG); and the group of Rosai–Dorfman disease and related histiocytoses (R group).1 JXG is the most common form of non-Langerhans cell histiocytosis, and is generally self-limiting and nonaggressive. Some reports have documented cases of children with LCH who have developed JXG after chemotherapy.2,3 In more than half of all cases of LCH, the BRAF V600E mutation can be detected.1 This mutation has never been reported in JXG with exclusive skin localization.