Pediatric Langerhans cell histiocytosis: state of the science and future directions.

Langerhans cell histiocytosis (LCH) is an inflammatory neoplasm of myeloid origin characterized by the presence of classic CD1a+/CD207+ cells. An ongoing debate over the grouping of LCH was finally settled in favor of neoplasm after the discovery of the BRAF V600E mutation in 2010. The pathologic cells were found to involve an almost universal activation of the MAPK/ERK pathway, with mutations identified in most kinases upstream of ERK (RAS/RAF/MEK).