MLLT1 and acute lymphoblastic leukemia: Pediatric ALL patients (n = 530) displayed the following rearrangements: AFF1 (n = 215; 40.6%), MLLT1 (n = 100; 18.9%), MLLT3 (n = 91; 17.2%), AFDN (n = 31; 5.8%), MLLT10 (n = 17; 3.2%), EPS15 (n = 8; 1.5%) and 26 other KMT2A rearrangements.