MAP2K1 and histiocytic neoplasm: Very recently, the report of the 2016 EAHP workshop on histiocytic neoplasms involving the lymph nodes documented 7 HS, of which 2 had BRAFV600E-, one a TP53 and one a MAP2K1 mutation (along with BCL2, BCL10, CDKN1B, CKIT) [35].