Clofarabine and Ara-C for the Treatment of Relapsed AML and Untreated MDS

Adult patients who are at least 18 years old with histologically confirmed disease as follows: * Standard or poor cytogenetic risk acute myelogenous leukemia (AML) according to the Southwestern Oncology Group (SWOG) criteria in first relapse or primary refractory status * Untreated high-risk myelodysplastic syndrome (MDS) defined as \>10% blasts * Chronic myelogenous leukemia (CML) in accelerated phase or blast crisis failing imatinib therapy. * Selected elderly patients with untreated AML who are at high risk of anthracycline toxicity. Inclusion Criteria: * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or * Laboratory values obtained less than or equal to 7 days prior to receiving study treatment: * Total bilirubin \< 2.0 mg/dL unless elevated due to hemolysis * Aspartate transaminase (AST)/alanine transaminase (ALT) less than or equal to 5 × upper limit of normal (ULN) * Serum creatinine \< 2.0 mg/dL * Capable of understanding the investigational nature, potential risks and benefits of the study, and able to provide valid informed consent. * Female patients of childbearing potential must have a negative serum pregnancy test within 2 weeks prior to enrollment. * Male and female patients must use an effective contraceptive method during the study and for a minimum of 6 months after study treatment. Exclusion Criteria: * Patients with FAB M3 unless relapsed after treatment with ATRA and arsenic trioxide. * Patients eligible to receive curative allogeneic transplant as determined by performance status, organ function, availability of a matched donor, etc. * Current concomitant chemotherapy, radiation therapy, or immunotherapy. * Use of investigational agents within 30 days or any anticancer therapy within 3 weeks before study entry. The patient must have recovered from all acute toxicities from any previous therapy. * Active heart disease including myocardial infarction within the preceding 3 months. * History of severe coronary artery disease, arrhythmias other than atrial flutter or fibrillation requiring medication, or uncontrolled congestive heart failure * Dyspnea at rest or with minimal exertion. * Patients with an active, uncontrolled systemic infection considered to be opportunistic, life-threatening, or clinically significant at the time of treatment or with a known or suspected fungal infection (ie, patients on parenteral antifungal therapy). * Pregnant or lactating patients. * Prior enrollment in this trial. * Any significant concurrent disease, illness, or psychiatric disorder that would compromise patient safety or compliance, interfere with consent, study participation, follow up, or interpretation of study results.