Dr. Raymond Bergan, professor in medicine-hematology/oncology and preventive medicine at Northwestern University, looks to the bloodstream for answers on how cells transform into metastatic killers. “When a woman gets a breast exam and a cancerous lump is discovered, it is not that lump that is going to kill her,” said Dr. Bergan. “The problem is metastasis; when that cancer spreads, it is often too late to be controlled.” As cancer spreads, cells from a primary tumor enter the blood and move to other parts of the body. The findings were published in Proceedings of the National Academy of Sciences of the United States.