In TCF3/PBX1-positive ALL, the most striking finding was that, in the majority of cases, a large region on 1q distal to the PBX1 locus was over-expressed whereas a small region (~1.6 Mb) on 19p distal to the TCF3 locus was under-expressed (Figure 6). This evidence concerns the gene PBX1 and acute lymphoblastic leukemia.