DFMO Maintenance for Patients With Relapsed/Refractory Ewing Sarcoma or Osteosarcoma

Inclusion Criteria: * Patients \< 40 years of age at the time of enrollment * Diagnosis of relapsed osteosarcoma or relapsed Ewing sarcoma who have completed all planned therapy for their relapse, as described in the protocol, and have no evidence of disease * Patients must have a performance status corresponding to Eastern Cooperative Oncology Group (ECOG) scores of 0, 1, or 2 * Myelosuppressive chemotherapy: At least 14 days must have elapsed since completion of myelosuppressive therapy * Monoclonal antibodies: At least 21 days must have elapsed from infusion of last dose of antibody, and toxicity related to prior antibody therapy must be recovered to Grade \< 2 * Biologic therapy (defined as anti-cancer agents not known to be myelosuppressive): At least 7 days after the last dose of agent * Radiation therapy: At least 14 days must have elapsed after local External Beam Radiation Therapy (XRT), at least 90 days after Total Body Irradiation (TBI), craniospinal XRT or if radiation to greater than 50% of the pelvis, and at least 42 days if other substantial bone marrow radiation * Adequate bone marrow function defined as: * Peripheral absolute neutrophil count (ANC) greater or equal to 750/microliter * Platelet count greater or equal to 75,000/microliter (transfusion independent) * Adequate renal function defined by serum creatinine based on age and gender (see protocol) * Adequate liver function defined as: * Total bilirubin ≤ 1.5 x the upper limit of normal (ULN) for age AND * SGPT (ALT) ≤ 5.0 x ULN for age. For this study the ULN is 45 U/L Exclusion Criteria: * Pregnant or breastfeeding females. Men and women of childbearing potential and their partners must agree to use adequate contraception while enrolled on this study. Based on the teratogenic potential of the agent, pregnant women will be excluded from this study. Because of potential risks to breastfed infants due to drug metabolites that could be excreted in breast milk, female patients who are lactating must agree to stop breastfeeding or will otherwise be excluded from this study. Females of childbearing potential must have a negative pregnancy test to be eligible for this study * Patients must not have an uncontrolled infection * Patients with a significant intercurrent illness (any ongoing serious medical problem unrelated to cancer or its treatment) that is not covered by the detailed exclusion criteria and that is expected to interfere with the action of study agents or to significantly increase the severity of the toxicities experienced from study treatment are not eligible