<b>Background/Objectives</b>: Langerhans cell histiocytosis (LCH) is a rare myeloid neoplasm characterized by the clonal proliferation of Langerhans-like dendritic cells and constitutive activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK-ERK) signaling pathway. This evidence concerns the gene MAPK1 and myeloid neoplasm.