PBX1 and acute lymphoblastic leukemia: In Paulsson et al’s study, only 18% of the cases had a balanced rearrangement [8], while 40% of TCF3-PBX1 positive cases overall have been found to have a balanced rearrangement [1], ultimately suggesting etiologically distinct subtypes of B-ALL with both hyperdiploidy and t(1;19)/der(19)t(1;19) based on the presence of the TCF3-PBX1 fusion gene by FISH and/or polymerase chain reaction (PCR) [8].