HLA mismatched donors in patients with myelodysplastic syndrome: an EBMT registry analysis

Recently, haplo-identical transplantation (haplo) using post-transplant cyclophosphamide (PTCy) has been reported to give very encouraging results in patients with hematological malignancies. Patients who have no HLA-matched donor currently have the choice between a mismatched unrelated donor, an unrelated cord blood donor and a haplo-identical related donor. The aim of our study is to compare the outcome of patients with myelodysplastic syndrome (MDS) who have been transplanted from a haplo-identical donor using PTCy, a HLA mismatched unrelated donor (marrow or peripheral blood stem cells) or an unrelated mismatched cord blood donor (CB). 833 MDS patients from the EBMT registry, transplanted between 2011 and 2016, were identified. The potential benefit of haplo was compared to mismatched unrelated and CB in an adjusted and weighted model taking into account potential confounders and other prognostic variables. Haplo was at lower risk of acute GVHD than mismatched unrelated donor (p=0.010) but at similar risk than CB. Progression-free survival was better after haplo (vs. mismatched unrelated, p=0.056, vs. CB, p=0.003) and overall survival tended to be superior after haplo (vs. mismatched unrelated, p=0.082, vs. CB, p=0.002). Non-relapse mortality was not significantly different between haplo and mismatched unrelated donor. Relapse risk was not influenced by the type of donor. In conclusion, patients with MDS from the EBMT registry receiving HSCT from a haplo donor have significant better outcome than CB and at least similar or better outcome than mismatched unrelated donor. Prospective studies comparing the type of donors will be needed to confirm this assumption.