Metastasis occurs when cancer cells penetrate the boundaries of the tumor’s tissue and infiltrate the walls of blood vessels or lymph vessels, gaining a means of transport to other parts of the body –- far from the original tumor site –- where they can then grow anew. This process is unique to cancer cells and is what makes the disease so dangerous –- and so feared. “A primary [cancerous] tumor can be removed,” explains the senior author of a new study, Alex Toker, of Beth Israel Deaconess Medical Center and assistant professor at Harvard Medical School. “But once the cancer has metastasized, it becomes intractable.” Scientists have known that in order for a tumor to metastasize, certain genes had to be “turned on” so that they could produce enzymes necessary to invade blood vessel walls and penetrate other tissues. New research has found that a protein known for its role in helping to provide the body’s immune system with a line of defense against infection is also in cancer cells that were removed from aggressive carcinomas of the breast and colon. This discovery could provide scientists with a promising new target for the development of a drug to halt tumor invasion and metastasis.