Researchers are using the polio virus to fight cancer cells in the brain.A team at Duke University is using a polio virus to infect tumor cells.It sets off an immune response that lasts for several months.The tumor goes away permanently.Dr. Matthias Gromeier began clinical trials more than three years ago.So far, 12 of 20 patients with a type of brain tumorcalled glioblastoma have responded well to the treatment.Gromeier said these patients had no chance of survival before the treatment.He added, "If you look at them today,you would not know they were cancer patients."This may seem like a miracle cure.But Gromeier pointed out that the approach has limits.It causes a toxic reaction that can cause brain swelling.This causes other side effects like muscle weakness and paralysis,seizures, limb swelling and tingling, speech impairment and headaches.Still, Gromeier said, "I am optimistic that we have identified the right doseand the right way to use our virusto get an immune response strong enough to fight the tumor,but not so strong to harm the patient."He called immunotherapy, "the most excitingand most promising development in cancer research."He said it would one day transform the way tumors are treated.Glioblastomas, the most common and lethal of all brain cancers,affect an estimated 240,000 people around the world per year.