ST. LOUIS, Missouri, Sept. 3 -- The Washington University School of Medicine issued the following news release: * * * Study sheds light on how pediatric brain tumors grow Blocking a chemical messenger in the brain that helps tumor cells multiply could offer new route to treatment * The most common type of brain tumor in children, pilocytic astrocytoma (PA), accounts for about 15% of all pediatric brain tumors. Although this type of tumor is usually not life-threatening, the unchecked growth  more