MAP2K1 and Langerhans cell histiocytosis: In addition to the BRAF mutation, somatic MAP2K1 mutations also showed high prevalence in BRAF V600E–negative Langerhans cell histiocytosis [35], both BRAF and MAP2K1 mutation plays its role in mitogen-activated protein kinase (MAPK) activation pathway, supporting the central role of ERK activation in LCH pathogenesis [36, 37].