Genetically engineered mouse models for CLL and aggressive B-cell lymphoma, specifically the Eμ-TCL1 mouse model of CLL [21] and the Eμ-Myc mouse model of aggressive MYC-induced B-cell lymphoma [22], are essential for studying leukemia/lymphoma pathogenesis and complex biological systems like chemokine receptor pathways in B-cell pathobiology. The gene discussed is MYC; the disease is B-cell chronic lymphocytic leukemia.