A 5 day course of fludarabine and cytarabine (FA) will be administered followed by full intensity conditioning regimen (Bucy) in the setting of allogeneic stem cell transplantation (SCT). The purpose of this study is to explore the antileukemic, immunosuppressive effects and safety of FA as the backbone of a conditioning regiment for the treatment of patients with high-risk, recurrent or refractory acute Leukemia and advanced myelodysplastic syndrome.

Inclusion Criteria:

• Signed written informed consent
• Aged between 0-65 years
• Patients suffering from either refractory de novo AML/ALL or relapsed AML/ALL or patients with very high risk AML/ALL in CR1
• Patients with advanced MDS
• Cardiac: Left ventricular ejection fraction ≥ 50%
• Adequate renal and hepatic function
• Performance status: Karnofsky ≥ 70%

Exclusion Criteria:

• Pregnant or lactating females
• Current participation in another clinical trial
• Contra-indication to one of the drug of the regimen
• 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 the agents included in the conditioning regimen

Patients with high-risk, recurrent or refractory acute leukemia and advanced myelodysplastic syndrome