A large (n = 756), multicenter, retrospective Nordic study analyzing the prognosis of various types of MLL fusion gene leukemia showed that MLL-AF4 and MLL-AF6 had a very poor prognosis with 10-year EFS of 29 and 11% and 10-year OS of 27 and 22%, respectively, while MLL-AF9 had 10-year EFS and OS of 50 and 63%, with a relatively good prognosis [26]. Here, AFF1 is linked to leukemia.