Case reports of MEK inhibitory therapy for patient with LCH with MAP2K1 p.E102_103del alteration showed lasting clinical improvement of lesions [42, 43], while a case of colonic adenocarcinoma with the same deletion showed progression on MEK and ERK inhibitory therapy [44] (Supplemental Table 3). Here, MAP2K1 is linked to Langerhans cell histiocytosis.