Unmanipulated haploidentical versus HLA-matched sibling allogeneic hematopoietic stem cell transplantation in relapsed/refractory acute myeloid leukemia: a retrospective study on behalf of the ALWP of the EBMT.

Refractory or relapsed acute myeloid leukemia (R/R-AML) has poor prognosis. Allogeneic hematopoietic stem-cell transplantation (HSCT) may provide cure in this scenario. We compared outcomes of HSCT from HLA-identical (HLA-id, n = 1654) sibling or haploidentical (Haplo, n = 389) donors in patients with R/R-AML, performed during the period 2007-2015. The Haplo group included patients receiving an unmanipulated graft (post-transplant cyclophosphamide, n = 278; in vivo T-cell depletion, n = 95; or both, n = 16). Median age at HSCT was 52 (range 18-74) years. Median follow-up was 16 and 22 months for HLA-id sibling and Haplo recipients, respectively (p = 0.11). Compared to MSD, Haplo HSCT were performed more recently (2013 vs 2011, p < 0.01), at longer interval from diagnosis (7 vs 5 months, p < 0.01), more frequently using bone marrow as stem cell source (47% vs 8%, p < 0.01) and with a reduced intensity conditioning regimen (50% vs 43%, p = 0.03). Engraftment was higher (93% vs 83%, p < 0.01) in HLA-id sibling. In multivariate analysis, Haplo HSCT was associated with lower GVHD/relapse-free survival, inferior LFS and OS and higher NRM, mainly due to a higher rate of infections (41% vs 25%, p < 0.01). For R/R-AML, HLA-id sibling donors remain the gold standard, when available, due to higher mortality in Haplo without significant gain in disease control.