Biomarkers in Blood Samples From Young Patients With Newly Diagnosed Brain Tumors Undergoing Standard Radiation Therapy and Chemotherapy

OBJECTIVES: Primary * Evaluate the fraction of peripherally circulating T-regulatory cells (T\_regs) in pediatric patients with newly diagnosed medulloblastoma and compare it to the levels found in a control group of patients undergoing craniectomy for Chiari malformation. * Evaluate the longitudinal effects of standard radiotherapy and chemotherapy regimens on the overall population of lymphocytes as well as the fraction of T\_reg cells in patients with medulloblastoma. Secondary * Determine the baseline fraction of T\_reg cells in those with non-medulloblastoma posterior fossa tumors compared to levels found in patients undergoing decompression for Chiari malformation. OUTLINE: This is a multicenter study. Patients with Chiari malformation and patients with posterior fossa tumor undergo standard surgery. Patients with posterior fossa tumor also receive standard radiotherapy and chemotherapy. Blood samples are collected at baseline and periodically to measure the level of circulating T-regulatory cells.