CXCL12 and neoplasm: To the extent that the chemokine CXCL12, which is found in blood and in organs commonly colonized by metastatic tumors, participates in promoting the migration of tumor cells across endothelium into those organs, our data suggest that the newly discovered CXCR7 receptor for CXCL12 may be a more effective therapeutic point of intervention than the previously studied CXCR4 receptor, which also recognizes CXCL12.