CD1A and Histiocytosis: Langerhans cell histiocytosis (LCH) is the most frequent type of histiocytosis, which is characterized by the accumulation of CD1a and CD207 positive histiocytosis with various inflammatory cells.[1] LCH is derived from immature myeloid dendritic cells with an oncological mutation in the mitogen-activated protein kinase pathway, which induces sustained activation of the extracellular signal-regulated kinase.