Decitabine in Treating Children With Relapsed or Refractory Acute Myeloid Leukemia or Acute Lymphoblastic Leukemia

Inclusion Criteria: * Histologically confirmed acute myeloid leukemia (AML) or acute lymphoblastic leukemia that is considered refractory to conventional therapy or for which no conventional therapy exists * For patients with AML: * M3 marrow * M2 marrow with at least 15% blasts * Secondary AML allowed * CNS involvement allowed * Performance status - Karnofsky 50-100% (age 17 to 21) * Performance status - Lansky 50-100% (age 16 and under) * At least 8 weeks * See Chemotherapy * WBC no greater than 30,000/mm\^3 * Patients with granulocytopenia, anemia, and/or thrombocytopenia are eligible but are not evaluable for hematological toxicity * Bilirubin no greater than 1.5 times normal * ALT no greater than 5 times normal * Albumin at least 2 g/dL * Creatinine no greater than 1.5 times normal * Creatinine clearance or radioisotope glomerular filtration rate at least lower limit of normal * Shortening fraction at least 27% by echocardiogram * Ejection fraction at least 50% by MUGA scan * No evidence of dyspnea at rest * No exercise intolerance * Oxygen saturation greater than 94% by pulse oximetry * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Concurrent seizure disorder allowed if well controlled on anticonvulsants * No grade 2 or greater CNS toxicity * No uncontrolled infection (i.e., infections associated with fever, dissemination, hemodynamic instability \[requiring pressor support\], and progression while on therapy) * No active graft-versus-host disease (GVHD) * GVHD well controlled on cyclosporine allowed * Recovered from prior immunotherapy * At least 1 week since prior biologic agents * At least 6 months since prior allogeneic bone marrow transplantation (BMT) * At least 3 months since prior autologous BMT * No concurrent sargramostim (GM-CSF) * No concurrent prophylactic filgrastim (G-CSF) during the first course of therapy * Recovered from prior chemotherapy * At least 4 weeks since prior cytarabine * At least 24 hours since prior cytoreductive therapy with hydroxyurea (20-30 mg/kg/day for no more than 7 days) to lower the WBC to no greater than 30,000/mm\^3 * No concurrent intrathecal therapy during the first course of decitabine * Recovered from prior radiotherapy * At least 2 weeks since prior local palliative radiotherapy (small port) * At least 6 weeks since prior cranial or craniospinal radiotherapy * No concurrent medications that induce cytidine deaminase or deoxycytidine kinase (e.g., cytarabine) * No concurrent medications that mask poor or deteriorating organ function * No concurrent CNS prophylaxis during the first course of decitabine * Concurrent anticonvulsants with no known interactions with decitabine allowed * Concurrent antibacterial or antifungal therapies for controlled infections allowed