AFF1 and leukemia: This collection spans the spectrum of KMT2Ar leukemia subtypes with diverse KMT2A translocations that create oncogenic fusion proteins with the transcriptional elongation factors AF4 (SEM, RS4;11, 1° ALL-1, 1° MPAL-2), AF9 (1° AML-3, 1° MPAL-1), ENL (KOPN-8, 1° AML-2), AF6 (ML-2) and AF10 (1° AML-4, 1° AML-5) as well as a relatively rare fusion to the cytoplasmic GTPase SEPT6 (1° AML-1) (Supplementary Table 1).