A20 leukemia cells express the CXCR4 chemokine receptor that guides them toward a chemokine gradient of CXCL12 (stromal cell-derived factor-1, SDF-1) actively produced by the biliary epithelium and bone marrow stromal cells (42, 43), which may account for the preferential metastatic behavior of A20 leukemia cells for these tissues. This evidence concerns the gene CXCL12 and leukemia.