PBX1 and acute lymphoblastic leukemia: Furthermore, approximately 50% of the Mexican children with ALL are classified into the high risk of relapse group and less than 20% are identified as positive for one of the four most common gene rearrangements associated with prognosis (ETV6/RUNX1, TCF3/PBX1, BCR/ABL1, and MLL/AF4) (6, 7).