This study is for a population of patients with few or no alternative options that was conducted to determine the response rate to clofarabine. Additionally the study will provide information on the safety profile, impact of overall survival, and impact on remission duration with clofarabine. It is a single arm study and has no comparator.

Note: This clinical trial was conducted by Bioenvision Ltd. Bioenvision Ltd. was acquired by Genzyme Corporation Oct 2007.

Inclusion Criteria:

• Have a diagnosis of ALL and confirmed by pathologic assessment.
• Be ≤ 21 years old at time of initial diagnosis.
• Eligible patients must have: Primary refractory disease; OR relapsed or refractory disease after a minimum of 2 prior blocks of treatment.
• Must not be eligible for therapy of higher curative potential.
• Have a Karnofsky Performance Status of ≥ 50 or Lansky Performance Scale of ≥ 30.
• Provide a signed, written informed consent from parent or guardian or young adult patients.
• Be able to comply with study procedures and follow-up examinations.
• Have adequate cardiac function without treatment.
• Have adequate organ function as indicated by the laboratory values for serum creatinine, serum bilirubin, AST and ALT, obtained within 7 days prior to registration.

Exclusion Criteria:

• Received previous treatment with clofarabine.
• Patients with isolated extramedullary disease.
• Have received prior BMT or PBSCT within the last 6 months.
• Have received prior BMT or PBSCT more than 6 months ago, but now has compromised organ function.
• Have an active, uncontrolled systemic infection.
• Are pregnant or lactating. Male and female patients who are fertile must agree to use an effective means of birth control to avoid pregnancy.
• Have a psychiatric disorder that would interfere with consent, study participation, or follow-up.
• Have received any other chemotherapy within the previous 2 weeks and must have recovered from acute toxicity oa all previous therapy prior to enrollment.
• Have any other severe concurrent disease.
• Have recent history of significant renal, hepatic or pulmonary dysfunction, or cardiac dysfunction or on treatment to support cardiac function.
• Have CNS disease.