New research suggests that the most dangerous part of any cancer is the thin, single-cell boundary where a tumor meets healthy tissue.Tumor cells that border normal tissue receive signals that instruct them to leave the tumor and travel through the body, resulting in the formation of deadly metastatic tumors in other locations, report researchers at Washington University School of Medicine in St. Louis.The findings, which appear in the Jan. 10 issue of the journal Developmental Cell, demonstrate the importance of a tumor’s environment. They also provide more information about the metastatic process and how it might be halted, the researchers said.