MAP2K1 and Langerhans cell histiocytosis: Prior observations of increased cytokines and growth factors, and regulatory T‐cell expansion in LCH patients, suggested a systemic inflammatory response.10 However, the recent discovery of mutations in the BRAF V600E or MAP2K1 oncogenes in over half of LCH patients, as well as clonality of the disease, strongly suggests that LCH is a neoplasm.11, 12, 13 This has significant implications on our understanding of LCH and its development.