Combination Chemotherapy in Treating Young Patients With Relapsed or Refractory Acute Leukemia

DISEASE CHARACTERISTICS:

* Must have 1 of the following diagnoses:

  * Acute lymphoblastic leukemia (ALL) meeting 1 of the following criteria:

    * Refractory to initial induction with two or more standard regimens
    * Relapsed \< 24 months after first complete response on a high-risk protocol OR refractory to one standard reinduction regimen
    * Second or greater relapse
  * Acute myeloid leukemia, acute biphenotypic leukemia, or acute undifferentiated leukemia meeting 1 of the following criteria:

    * Refractory to initial induction
    * First or greater relapse
* Must have \> 20% bone marrow blasts, or evidence of recurrent disease at an extramedullary site
* No symptomatic CNS disease

  * Patients with asymptomatic CNS disease are eligible with the approval of the principal investigator

PATIENT CHARACTERISTICS:

* Karnofsky performance status (PS) 70-100% OR Lansky PS 70-100%
* AST and ALT \< 4 times upper limit of normal
* Bilirubin \< 2.0 mg/dL (unless liver involvement)
* Creatinine within normal range for age OR creatinine clearance \> 60 mL/min/1.73 m\^2
* Adequate cardiac function (either asymptomatic with no prior risk factors, or if symptomatic, left ventricular ejection fraction \> 50% at rest)
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception
* No active uncontrolled viral, bacterial, or fungal infection

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* No prior clofarabine
* More than 2 weeks since prior systemic chemotherapy

  * At least 7 days since prior chemotherapy for patients with rapidly progressive disease and recovered