It was recently shown that approximately 54% of the patients with ECD and 57% of patients with Langerhans cell histiocytosis harbor a somatic gain-of-function mutation (p. V600E) in the protooncogene BRAF. This mutation leads to activation of the tumorigenic RAS-ERK pathway and is thought to play a key role in the pathogenesis of the disorder [15]. The gene discussed is BRAF; the disease is Langerhans cell histiocytosis.