Patients with certain tumor types (medulloblastoma, PNET, ependymoma, malignant germ cell tumor and pineoblastoma) or who have symptoms that indicate there might be tumor along the spinal cord may have a spinal tap. For this procedure, the patient lies on the side and a needle is inserted between two vertebrae (bones of the spine) in the lower back, into the cerebrospinal fluid space. A sample of fluid is drawn for testing for cancer cells. If the tumor has spread through the spinal fluid, a spinal tap will be done every other cycle (every 2 months) to monitor the effects of therapy.