In the last decade, the gain-of-function BRAFV600E mutation was observed to be recurrent in the histiocytic disorders Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD), characterized by the infiltration of CD1a+CD207+ and CD68+CD1a− clonal mononuclear phagocytes, respectively [1]. This evidence concerns the gene CD1A and Erdheim-Chester disease.