MAPK1 and Langerhans cell histiocytosis: Research suggests that in cases where pathological results are unclear or tissue is unavailable, the possibility of diagnosing LCH can be increased by testing for mutations of BRAF, MAP2K1 (mitogen-activated protein kinase kinase 1), ARAF, CCND1 (cyclin D1), or other components of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling pathway in blood or bone marrow (12–14).