Langerhans Cell Histiocytosis With <i>MAP2K1^E102_I103del</i> Mutation Successfully Treated With Trametinib

The discovery of the MAPK pathway mutations in lesions of patients with Langerhans cell histiocytosis (LCH) has made targeted therapy an important therapeutic approach for these patients. Theoretically, the RAF-independent mutation <i>MAP2K1^E102_I103del</i> is naturally resistant to allosteric MEK inhibitors. We report a dramatic response to MEK inhibitor trametinib in a case of LCH with <i>MAP2K1^E102_I103del</i> mutation, which indicates that trametinib is worth trying in recurrence and refractory LCH patients with <i>MAP2K1^E102_I103del</i> . <b>Trial Registration</b>: The authors have confirmed clinical trial registration is not needed for this submission.