MAP2K1 and neoplasm: Apart from MAP2K1, other gene mutations were far less common in HCLv/HCLc-IGHV4-34 exomes [13], indicating that the MAP2K1 mutation is dominant and a driver in atypical HCL origins and progression (i.e. in HCLv/HCLc-IGHV4-34 tumours).