This is a multicenter, multinational, non-randomized, non-controlled open-label phase II trial to evaluate the safety and efficacy of treosulfan in a combination regimen with fludarabine as conditioning therapy prior to allogeneic stem cell transplantation (SCT) in patients with MDS.

The aim is to demonstrate a clinical benefit compared to historical data with intravenous busulfan.

Inclusion Criteria:

1. Patients with myelodysplastic syndrome, (MDS) according to WHO classification (< 20 % myeloblasts in peripheral blood or bone marrow at initial diagnosis) indicated for allogeneic transplantation
2. Availability of an HLA-identical sibling donor (MRD) or HLA-identical unrelated donor (MUD) HLA-identity defined by the following markers: HLA-A, -B, -DRB1, DQB1.
3. Target graft size (unmanipulated) bone marrow: 2 to 10 x 106 CD34+ cells/kg BW recipient or at least 2 x 108 nucleated cells /kg BW or peripheral blood: 4 to 10 x 106 CD34+ cells/kg BW recipient
4. Age > 18 and < 60 years
5. Karnofsky Index > 80 %
6. Adequate contraception in female patients of child-bearing potential
7. Written informed consent

Exclusion Criteria:

1. 'Secondary' or therapy-related MDS with known history of exposure to cytotoxic alkylating drugs and/or radiation therapy
2. Previous AML-induction therapy with more than two courses (e.g. in case of blast excess)
3. Previous allogeneic transplantation
4. Severe concomitant illnesses / medical conditions (e.g. impaired respiratory and/or cardiac function)
5. Known and manifested malignant involvement of the CNS
6. Active infectious disease
7. HIV- positivity or active hepatitis infection
8. Impaired liver function (Bilirubin > upper normal limit; Transaminases > 3.0 x upper normal limit)
9. Impaired renal function (Creatinine-clearance < 60 ml/min; Serum Creatinine > 1.5 x upper normal limit).
10. Pleural effusion or ascites > 1.0 L
11. Pregnancy or lactation
12. Known hypersensitivity to treosulfan and/or fludarabine
13. Participation in another experimental drug trial within 4 weeks before study
14. Non-co-operative behaviour or non-compliance
15. Psychiatric diseases or conditions that might impair the ability to give informed consent