In children and adolescents with chronic myeloid leukaemia (CML) stem cell transplantation (SCT) may be a valid alternative to the life-long treatment with tyrosinkinase inhibitors (TKI). This trial aims to evaluate the use of a reduced intensity conditioning regimen (RIC), consisting of fludarabine, melphalan and thiotepa in order to minimize transplant related mortality and toxic late effects. Strict post-transplant monitoring and reintroduction of TKI as well as donor lymphocyte infusions (DLI) in case of relevant residual disease are part of the protocol.

Chronic myeloid leukaemia (CML) is a rare disease in children with an incidence of 3-5% of all paediatric leukaemias. Since the introduction of tyrosinkinase inhibitors (TKI) stem cell transplantation (SCT) is no longer the first choice treatment for patients with early phase CML.

However life-long treatment with TKI may not be feasable in several cases due to side effects such as growth retardation, non-compliance and resistance. This protocol evaluates the feasibility of SCT following a reduced intensity conditioning regimen (RIC) consisting of fludarabine, melphalan, thiotepa and thymoglobuline (ATG). Matched siblings and matched unrelated donors are permitted for stem cell donation. In case of unrelated donors tissue typing has to be done by high resolution molecular typing. Donors with 10/10 or 9/10 identical allels in the human leukocyte antigen (HLA) system are accepted. Preferred stem cell source is bone marrow but peripheral blood stem cells and umbilical cord blood are also allowed. Graft-versus-Host-Disease (GvHD)-prophylaxis is achieved with cyclosporine A and mycophenolate mofetil.

Monitoring of the breakpoint cluster region - Abelson (BCR/ABL) rearrangement is performed monthly in the first year after SCT. In case of BCR/ABL positivity TKI are given in the first year after SCT. Followed by donor lymphocyte infusions (DLI) later on if BCR/ABL positivity persists.

Inclusion Criteria:

• children and adolescents with BCR/ABL positive CML in chronic phase, who are eligible for allogeneic stem cell transplantation, irrespective of the previous treatment strategy
• availability of a HLA matched sibling donor (MSD), a matched family donor, a matched unrelated donor or a matched unrelated cord blood (MD)
• informed consent

Exclusion Criteria:

• unavailability of MSD or MD
• patients in accelerated phase or blast crisis
• pregnancy
• previous autologous or allogeneic SCT
• no informed consent