The role of chemoattraction in cancer metastases.

It has long been unclear as to why particular cancers preferentially metastasize to certain sites. The possibilities usually discussed involve differential survival and proliferation at these sites, or selective trapping with or without preferential homing. A recent report by Muller et al.(1) provides evidence for preferential homing of breast cancer to metastatic sites. The findings indicate that the chemokine receptors CXCR4 and CCR7 are found on breast cancer cells and their ligands are highly expressed at sites associated with breast cancer metastases. This results in chemotaxis, or directed migration of tumor cells from their primary site via the circulation to the preferential sites of metastases. The evidence for this model and its significance are reviewed here.