A Phase III Randomized, Double-blind, Controlled Study Comparing Clofarabine and Cytarabine Versus Cytarabine Alone in Adult Patients 55 Years and Older With Acute Myelogenous Leukemia (AML) Who Have Relapsed or Are Refractory After Receiving up to Two Prior Induction Regimens

Inclusion Criteria:

- Have a diagnosis of Acute Myelogenous Leukemia (AML) according to World Health
Organization (WHO) classification

- Relapsed after receiving up to 2 prior induction regimens (i.e. first or second
relapse)or are refractory to not more than one prior combination chemotherapy
induction regimen

- Be ≥ 55 years of age

- Have an Eastern Cooperative Oncology Group (ECOG) score of 0-2

- Be able to comply with study procedures and follow-up examinations

- Be nonfertile or agree to use birth control during the study through the end of
treatment visit and for at least 90 days after the last dose of study drug

- Have adequate liver and renal function as indicated by certain laboratory values

Exclusion Criteria:

- Received previous treatment with clofarabine

- Received bolus, intermediate or high-dose cytarabine as induction therapy unless
certain remission criteria are met

- Have received a hematopoietic stem cell transplant (HSCT) within the previous 3
months

- Have moderate or severe graft versus host disease (GVHD), whether acute or chronic

- Are receiving any other chemotherapy or investigational therapy. Patients must have
been off prior AML therapy for at least 2-6 weeks prior to entering study.

- Have a psychiatric disorder that would interfere with consent, study participation,
or follow-up

- Have an active, uncontrolled infection

- Have any other severe concurrent disease, or have a history of serious organ
dysfunction or disease involving the heart, kidney, liver, or other organ system

- Have been diagnosed with another malignancy, unless disease-free for at least 5
years; patients with treated nonmelanoma skin cancer, in situ carcinoma, or cervical
intraepithelial neoplasia, regardless of the disease-free duration, are eligible for
this study if definitive treatment for the condition has been completed; patients
with organ-confined prostate cancer with no evidence of recurrent or progressive
disease are eligible if hormonal therapy has been initiated or the malignancy has
been surgically removed.

- Have clinical evidence suggestive of central nervous system (CNS) involvement with
leukemia unless lumbar puncture confirms absence of leukemic blasts in the
cerebrospinal fluid(CSF)

- Known HIV positivity

- Are pregnant or lactating