AML SCT-BFM 2007: Results of the Prospective Hematopoietic Stem Cell Transplantation (HCT) Trial of the Berlin-Frankfurt-Münster (BFM) Study Group for Children with Very High Risk Acute Myeloid Leukemia

BACKGROUND: Pediatric AML represents a rare and heterogeneous disease. Within the BFM study group, HCT for this patient cohort was performed with considerable inter-center variability. AML SCT-BFM 2007 was based on a transplantation consensus and aimed to prospectively generate a reliable body of data on which further transplantation technologies could be based.

METHODS: AML SCT-BFM 2007 was conducted according to current legislation as an international multicenter clinical trial (EudraCT: 2007-004517-34, NCT00606723), data were collected via a specifically developed remote data entry (RDE)-based data bank, and verified against source data by an on-site monitoring program. Children with cytogentic and molecular high-risk features achieving a complete first remission (CR1) and those in CR2 after a first relapse qualified for HCT from a matched donor (MD). A MD was defined to be identical when at least 9/10 alleles on the HLA-A, B, C, DRB1 and DQ loci did match. A myeloablative conditioning regimen consisting of Busulfan (age adjusted i.v. dosing: 3.2 - 4,8 mg/kg BW on days -7 through -4), Cyclophosphamide (60mg/kg iv on days -3 and -2), and Melphalan (140 mg/m² on day -1) termed BuCyMel was used. For GVHD prophylaxis CSA and short term MTX were given, for unrelated donors anti-thymocyte globulin (ATG Neovii) was added. Children with refractory primary disease or refractory relapse were eligible for early transplantation. A cytoreductive regimen containing Fludarabine (30mg/m²/d i.v.), Amsacrine (100 mg/m²/d i.v.) and Cytarabine (2g/m²/d i.v.) all on days -12 through -9 (FLAMSA) was immediately followed by a reduced intensity conditioning (RIC) consisting of 4 Gy TBI and Cyclophosphamide (60 (unrelated)/40 (related) mg/kg/d i.v.) on days -4 and -3. After early taper of immunosuppression (MMF halted by day 40 and CSA after taper by day 90) increasing doses of prophylactic donor lymphocyte infusions (DLI) were given on days 120, 150, and 180. Standard statistical methods were used for the analysis of event-free survival (EFS, events: relapse, death from any cause), overall survival (OS), cumulative incidence of treatment related mortality (TRM) and relapse (CIR) after HCT.

RESULTS: Recruitment was conducted between 5/2010 and 2/2016. 97 children underwent HCT after conditioning with BuCyMel. Median neutrophil engraftment was achieved after 21 days (range 9-38). 3-year EFS and OS were 62%, standard error (SE) 5%, and 73%, SE 5%. CIR was 22%, SE 4%. Median time to relapse was 8 months (range 1-66) after HCT. TRM was 15%, SE 4%, with 8/15 patients dying before day 100. TRM correlated with age with a rate of 9% in children younger than 12 years (n = 68) and 31% in older children and adolescents (Fig. A). This resulted in a stop of using BuCyMel for older children and adolescents in 6/2014. The rate of acute graft versus host disease (aGVHD) grade II-IV was 22%, chronic GVHD developed in 11%. Median neutrophil engraftment for children transplanted for refractory disease (n= 35) was 23 days (range 10-34). 3-year EFS and OS were 46%, SE 8%, and 51%, SE 9%. EFS for primarily refractory disease was 53%, SE 11%, whereas EFS for refractory relapses (n = 7) was 29%. Relapse rate was 43%, SE 9%, and TRM reached 11%, SE 5% (Fig. B). Acute and chronic GVHD rates were at 26% and 17%.

CONCLUSION: Within a well-defined trial concept HCT from a matched donor using BuCyMel for conditioning results in an EFS of 60% with a low TRM rate in younger children. The identical approach is associated with a high TRM rate of 31% in older children and adolescents. Whether the use of alternative conditioning strategies in this population can reduce mortality while maintaining the relapse-free survival rates remains to be determined. In high-risk patients with refractory disease, early use of RIC HCT followed by the infusion of prophylactically given DLI can induce long-term remissions in more than 50% of children without increasing the risk for GVHD.

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