B-lymphoblastic leukemia/lymphoma (LBL/L) is an aggressive subtype of leukemia/lymphoma that can be associated with specific genetic abnormalities, such as a translocation between the TCF3 gene on chromosome 19 and the PBX1 gene on chromosome X or a translocation of the IGH gene on chromosome 14 and IL3, resulting in the fusion gene product TCF3-PBX1 or IGH-IL3, respectively. The gene discussed is IL3; the disease is leukemia.