Langerhans cell histiocytosis associated with chronic myelomonocytic leukemia both harboring the same BRAF V600E mutation: efficacy of vemurafenib.

Langerhans cell histiocytosis (LCH) is a rare proliferative disorder characterized by inflammatory lesions with abundant CD1a+, langerin+/CD207+ dendritic cells. Clinical behavior of LCH ranges from limited skin involvement to life-threatening multiorgan disease. Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping myelodysplastic/myeloproliferative features. We report the case of a patient fulfilling criteria for multiorgan LCH and CMML, harboring the same BRAFV600E mutation and treated successfully with vemurafenib, suggesting that both entities may belong to a range of manifestations of the same pathologic process.