A. (left) Schematic of MAPK pathway. Under physiologic conditions, the growth factor (gray box) engages the tyrosine kinase receptor that transduces the signal to the nucleus. (right) Activating mutations (such as BRAF-V600E) drive constitutive ERK activation. In the case of LCH, this drives the expression of anti-apoptosis BCL2L1 (BCL-xL) and inhibits CCR7.
B. Stacked bar graphs represent percentages of MAPK pathway mutations in each histiocytic histologic subtype.