Clofarabine Salvage Therapy in Patients With Relapsed or Refractory Acute Myeloid Leukemia (AML)

Inclusion Criteria: * Diagnosis of AML according to WHO criteria. * Untreated relapse or refractory disease after a minimum of one standard induction therapy. Treatment of relapse with leukocyte-apheresis or up to 5 days with low dose cytarabine or hydroxyurea is allowed. * Refractory disease is defined as ≥5% blasts after the second cycle of induction therapy or no reduction in marrow blasts at early treatment assessment (day +15) after the first cycle of induction therapy. * Relapse is defined as an increase in bone marrow blast count ≥5%, re-appearance of blasts in the peripheral blood or extramedullary disease. * Age above 40 years. * Have adequate renal and hepatic functions as indicated by the following laboratory values: * Serum creatinine \<=1.0 mg/dL; if serum creatinine \>1.0 mg/dL, then the estimated glomerular filtration rate (GFR) must be \>60 mL/min/1.73 m2 (see reference below\*) * Serum bilirubin \<=1.5× upper limit of normal (ULN) * Aspartate transaminase (AST)/alanine transaminase (ALT) \<=2.5× ULN * Alkaline phosphatase \<=2.5× ULN * Eligibility for intensive chemotherapy * Patient needs to be capable to understand the clinical trial as an investigational approach to bridge the time to potential allogeneic HCT, potential risks and benefits of the study. * Signed written informed consent. * Female patients of childbearing potential must have a negative serum * 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: * For refractory disease, more than two prior induction chemotherapies or more than one prior salvage chemotherapy containing high-dose cytarabine (cumulative dose of cytarabine ≥ 5 g/m2). * Second or higher relapse. Patients who received hypomethylating agents like azacytidine or decitabine as a treatment of first relapse, respond and relapse later on may be included. * Acute promyelocytic leukemia with t(15;17)(q22;q12) molecular detection or (PML/RARα). * Central nervous system involvement (i.e. WBC ≥ 5/µL in cerebrospinal fluid with blasts present on cytospin). * Prior allogeneic HCT * Autologous transplantation within 100 days prior to start of study treatment * Use of investigational agents or anticancer therapy within 10 days before study entry with the exception of hydroxyurea or low-dose cytarabine. * 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 that may place the patient at undue risk to undergo transplantation. * Patients with known refractoriness to platelet support. * Patients with a systemic fungal, bacterial, viral, or other infection not controlled (defined as exhibiting ongoing signs/symptoms related to the infection and without improvement, despite appropriate antibiotics or other treatment). * Pregnant or lactating patients. * 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.