Distritubution of non-BRAF^V600E mutations. (A) Allele burden of MAPK mutations at diagnosis according to clinical stage: SS, RO⁻ MS-LCH, or RO⁺MS-LCH. (B) Distribution of MAPK mutations in PBMCs from patients with MS-LCH sorted into quadrants as shown according to expression of HLA-DR and lineage antigens (CD3, CD19, CD20, and CD56). Area of each quadrant in the pie is proportional to the total number of mutant alleles (mutated allele fraction multiplied by number of cells in the quadrant). (C) Distribution of MAPK mutations among PBMCs from patients with MS-LCH showing the percentage of mutated alleles detected. Red shading indicates positive fractions weighted by abundance within each sample. B, B cell; mono, monocyte; nt, not tested; pDC, plasmacytoid DC. *P < .05, **P < .001 by Mann-Whitney test (excluding patients with BRAF^V600E).