The majority of MLL-r leukemias involve fusions of MLL with one of six common partner genes: AF4 [t(4,11)], AF9 [t(9,11)], ENL [t(11,19)(q23,p13.3)], AF10 [t(10,11)], ELL [t(11,19)(q23,p13.1)], or AF6 [t(6,11)] (29). Here, AFF1 is linked to leukemia.