Comparable survival outcomes with haploidentical stem cell transplantation and unrelated bone marrow transplantation

We retrospectively compared outcomes of unrelated donor bone marrow transplant (UBMT) and HLA-haploidentical peripheral blood stem cell transplantation using post-transplant cyclophosphamide (PTCy-haploPBSCT) using the Japanese registry data. Recipients of first HCT for acute leukemia and myelodysplastic syndromes between 2012 and 2015 were included. The analyzed subjects comprised UBMT recipients with 8/8 matched HLA alleles (n = 1470), 7/8 matched alleles (n = 859), 6/8 matched alleles (n = 186), and recipients of PTCy-haploPBSCT (n = 133). In multivariate analyses with 8/8 matched UBMT as the reference, PTCy-haploPBSCT showed similar overall mortality, decreased risk of non-relapse mortality (NRM), increased risk of relapse, and decreased risk of grade II-IV acute graft-versus-host disease (GVHD) and chronic GVHD. Adjusted probabilities for 8/8 matched UBMT, PTCy-haploPBSCT, and 7/8 and 6/8 matched UBMT groups at 2 years post-transplant were 61%, 60%, 58%, and 52% for overall survival, 23%, 28%, 21%, and 19% for relapse, and 20%, 7%, 24%, and 33% for NRM. PTCy-haploPBSCT was associated with remarkably low NRM, contributing to survival outcomes that were comparable to 8/8 matched UBMT. The higher relapse rate in the PTCy-haploPBSCT group might be associated with the higher proportion of high-risk patients. PTCy-haploPBSCT may be a viable alternative when HLA-matched related donors are not available.