Tumor's border cells told to leave.

Cells on a tumor's outer layer that touch healthy tissue receive a chemical signal that sends them wandering away, according to new research. The finding could eventually lead to new ways to stop metastasis, the process by which cancers spread.

Scientists traditionally study metastasis by observing tumors cultured in a lab dish. According to Ross Cagan, a developmental biologist at Washington University School of Medicine in St. Louis, these cultured cells may not truly represent how tumors behave in the body.

To study metastasis in an organism, Cagan and his colleagues created tumors in fruit flies by turning on a cancer-promoting gene called Src.

Once the tumors began to grow, the researchers found that cancerous cells touching healthy cells gradually lost surface proteins that kept them anchored. When they detached, the tumor cells "literally walked around the body; says Cagan.

Most of these motile cells died after moving away from the tumor. However, Cagan suggests that if additional mutations were to keep the cells alive, they could multiply and form tumors elsewhere in the body.

The team's preliminary investigations suggest that the chemical that sends tumor cells on their way is a protein called cadherin, which is secreted by healthy cells.

"Knowing what this signal is could give us a big step up on stopping the signal; says Cagan. He and his team report their findings in the January Developmental Cell.--C.S.