AFF1 and acute lymphoblastic leukemia: Chromosomal rearrangements of the KMT2A gene can produce many different chimeric TFs through in-frame fusions with various partner genes [30], in ALL most commonly resulting in KMT2A::AFF1 (AF4) and KMT2A::MLLT1 (ENL) fusions through t(4;11) and t(11;19) rearrangements, respectively.