MAP2K1 and histiocytic neoplasm: We identified 14 reports; among them, antitumour activity was shown for the BRAF V600 kinase inhibitor vemurafenib in adult patients with Erdheim–Chester disease (ECD) and Langerhans cell histiocytosis (LCH) harbouring BRAF V600 mutation, vemurafenib combined with cladribine and cytarabine in children with BRAF V600E-positive LCH with or without risk organs, the BRAF inhibitor dabrafenib as monotherapy and in combination with the MEK1/2 inhibitor trametinib in children with BRAF V600-mutant LCH, and the MEK1/2 inhibitor cobimetinib in adult patients with histiocytic neoplasms (LCH and ECD).