Within 2 weeks of starting the study, subject's medical history and current medical conditions will be recorded. A physical examination including vital signs (temperature, respiratory rate, blood pressure, and pulse), height and weight, and neurological examination will be done. Subject will be asked about his or her ability to perform everyday tasks. Blood tests for assessment of a complete blood count including monitoring liver and kidney function and a urine test to check kidney function will be performed. For women of childbearing potential, a blood test to rule out pregnancy will be done prior to the start of treatment. Blood tests will also check for a specific gene, which may affect how much irinotecan subject is given. A magnetic resonance imaging (MRI) of will be performed within 2 weeks before starting study drugs as well as after every eight weeks to determine response and progression.