BCL9 and acute lymphoblastic leukemia: Although IGH is rearranged to a variety of cytokine receptors and transcription factor genes in ALL, including CRLF2, EPOR and members of the CEBP family of transcription factors18, 19, 20, 21, and multiple known and novel IGH rearrangements, were identified (Supplementary Data 1), none of the BCL9 rearrangements identified in this study involved IGH. BCL9 is a component of the WNT/β-catenin signalling cascade that has important roles in development, stem cell self-renewal and oncogenesis.