BRAF mutated cfDNA has been identified in the plasma of patients with both BRAF mutated metastatic melanoma and systemic histiocytoses including Langerhans Cell Histiocytosis and Erdheim-Chester disease (ECD), a form of non-Langerhans cell histiocytosis characterized by multi-system tissue infiltration of cells derived from monocyte/macrophage lineage [4, 12, 13]. This evidence concerns the gene BRAF and Erdheim-Chester disease.