Emissaries set up new sites

摘要

The capacity of tumours to spread to other organs is one of their most dangerous attributes. A study of how cancer cells settle in new places shows that they send out envoys to prepare the ground for them. During the process of metastasis, tumour cells move from the primary tumour to colonize another organ. But why do these mobile cells put down roots only in particular organs, or only at specific sites within an organ? The lungs and liver, for example, seem particularly popular secondary targets for tumour cells. Some studies imply that this 'preference' might occur because, as they branch out within those organs, the blood vessels become very narrow, and the blood-borne tumour cells are trapped when they enter the fine capillary beds. Other work has identified proteins that are specific to the cells lining the capillaries of certain tissues as possibly promoting metastasis formation. A report from Kaplan et al. (page 820 of this issue) provides another explanation. The authors show that tumour cells can mobilize normal bone-marrow cells, causing them to migrate to particular regions and change the local environment so as to attract and support a developing metastasis.