Glutamine in Treating Neuropathy Caused by Vincristine in Young Patients With Lymphoma, Leukemia, or Solid Tumors

Inclusion Criteria: * Patients between the age of 5 and 21 years old. * Patients who demonstrate the ability to complete the assessment instruments at baseline. * Patients who are diagnosed with leukemia or solid tumors and are expected to receive a cumulative dose of \> or = to 6mg/m2 of vincristine, or \> 6mg if individual vincristine doses are capped at 2mg according to primary cancer treatment protocol, over a 30-week period. Exclusion Criteria: * Patients with primary CNS tumors other than medulloblastoma or patients with CNS metastasis. * Patients with recurrent disease. * Patients with Grade II, III or IV neurological status by the NCI CTC (Ver. 3.0) on clinical exam. * Patients who have already received \> 8mg/m2 of vincristine, or \> 8mg if individual vincristine doses are capped at 2mg according to primary cancer treatment protocol, during their course of therapy at time of consent. * Patients with hepatic encephalopathy or hyperammonemia. * Patients with a focally abnormal neurologic exam.