Researchers say a virus once feared around the world can help to treat some kinds of cancer in the brain. The researchers are with the Duke University Health System in the American state of North Carolina. These doctors say they used genetically engineered polio virus to treat people with an aggressive and deadly brain tumor. The survival rate for people with this form of cancer, called glioblastoma, is very low. They usually live no longer than two years after the disease is discovered. The brain tumors often return after they are treated the first time.