Haploidentical vs. unrelated allogeneic stem cell transplantation for acute lymphoblastic leukemia in first complete remission: on behalf of the ALWP of the EBMT.

Unmanipulated haploidentical allogeneic stem cell transplantation (Allo-SCT) has become an attractive alternative for patients lacking HLA-matched sibling or unrelated donors. However, data of outcome in ALL is still scarce. The outcomes of 1234 adult patients with ALL in first complete remission (CR1) who underwent Allo-SCT between 2007 and 2016 were analyzed. Comparison was done between haploidentical donor (Haplo) (136 patients), matched unrelated donor (MUD 10/10) (809 patients), and mismatched unrelated donor (MMUD 9/10) (289 patients). Univariate analysis showed similar outcomes in Haplo, MUD, and MMUD, including OS, LFS, RI, NRM, AGVHD, and CGVHD. In multivariate analysis, Haplo was not associated with worse outcomes compared to MUD 10/10 and MMUD 9/10. Indeed, compared to Haplo, the hazard ratio (HR) for LFS, OS, RI, NRM, AGVHD, and CGVHD were 1.1 (p = 0.7), 0.9 (p = 0.4), 1.35 (p = 0.2), 0.7 (p = 0.2), 1.1 (p = 0.8), and 0.8 (p = 0.2) for MUD, respectively, and 1.1 (p = 0.8), 1.0 (p = 1.0), 1.2 (p = 0.3), 0.8 (p = 0.4), 1.2 (p = 0.3), and 0.9 (p = 0.6) for MMUD, respectively. In conclusion, outcomes of adult patients with ALL in CR1 receiving Haplo Allo-SCT are comparable to MUD or MMUD transplants. Haplo should be considered as a clinically relevant option for patients lacking a matched sibling donor.