The ability of MDA-MB-231 human breast cancercells (a cell line that is metastastic in experimental models) to migratetowards protein extracts of lung and liver, or to produce lung and lymph nodemetastasis after tail-vein injection or orthotopic implantation, was inhibited byneutralizing anti-CXCR4 and/or anti-CXCL12 antibodies. This evidence concerns the gene CXCL12 and neoplasm.