Misguided myeloid differ-entiation model for LCH ontogeny according to different risk groups. According to this model, the extent of disease is defined by the differ-entiation stage of the cell in which the activating somatic MAPK mutation occurs. Abbreviations: DC, dendritic cell; LCH, Langerhans cell histiocytosis.|@|~(^,^)~|@|MAPK pathway mutations in LCH. Activating MAPK pathway mutations in LCH drive pathologic ERK activation. Abbreviations: A-Raf, rapidly accelerated fibrosarcoma isoform A; B-Raf, rapidly accelerated fibrosarcoma isoform B; C-Raf, rapidly accelerated fibrosarcoma isoform C; ERK, extracellular signal-regulated kinase; GPCR, G-protein-coupled receptor; LCH, Langerhans cell histiocytosis; MAPK, mitogen-activated protein kinase; MEK, mitogen-activated protein kinase kinase; Ras, rat sarcoma.