Recently, knock-in mice models for E2A-HLF and E2A-PBX1 involving fusion genes in B-lineage acute lymphoblastic leukemia (B-ALL) have demonstrated that enhanced expression of Zfp521, the murine counterpart of human ZNF521, cooperates to leukemia transformation, and an upregulation of ZNF521 was found in human B-ALL samples bearing E2A-HLF or E2A-PBX1 fusion oncogenes. This evidence concerns the gene PBX1 and precursor B-cell acute lymphoblastic leukemia.