The report has also suggested that ECD should be redefined as an inflammatory myeloid neoplasia, because it is based on a background of chronic inflammation, mutations in the mitogen-activated protein kinase (MAPK) pathway are found in ECD and LCH [41], and deregulated activation of the MAPK pathway due to oncogenic mutations in the BRAF, NRAS, PIK3CA, and MAP2K1 genes is central to the pathogenesis of ECD [40]. Here, MAP2K1 is linked to Langerhans cell histiocytosis.