Haploidentical donors offer a potentially readily available donor, especially for non-White patients, for hematopoietic cell transplantation (HCT). In this North American collaboration, we retrospectively analyzed outcomes of first HCT using haploidentical donor and posttransplantation cyclophosphamide (PTCy) in MDS/MPN-overlap neoplasms (MDS/MPN). We included 120 consecutive patients who underwent HCT using a haploidentical donor for MDS/MPN across 15 centers. Median age was 62.5 years and 38% were of non-White/Caucasian ethnicity. The median follow-up was 2.4 years. Graft failure was reported in 7/120 (6%) of patients. At 3 years, nonrelapse mortality (NRM) was 25% (95%CI 17-34%), relapse 27% (95%CI 18-36%), grade 3-4 acute graft versus host disease (GVHD) 12% (95%CI 6-18%), chronic GVHD requiring systemic immunosuppression 14% (95%CI 7-20%), progression-free survival (PFS) 48% (95%CI 39-59%), and overall survival (OS) 56% (95%CI 47-67%). On multivariable analysis, NRM was statistically significantly associated with advancing age at HCT (per decade increment, sdHR 3.28, 95%CI 1.30-8.25); relapse with the presence of mutation in EZH2/RUNX1/SETBP1 (sdHR 2.61, 95%CI 1.06-6.44); PFS with advancing age at HCT (per decade increment, HR 1.98, 95% 1.13-3.45); and OS with advancing age at HCT (per decade increment, HR 2.01, 95% CI 1.11-3.63) and splenomegaly at HCT/prior splenectomy (HR 2.20, 95%CI 1.04-4.65). Haploidentical donors are a viable option for HCT in MDS/MPN, especially for those disproportionately represented in the unrelated donor registry. Hence, donor mismatch should not preclude HCT for patients with MDS/MPN, an otherwise incurable malignancy. In addition to patient age, disease-related factors including splenomegaly and high-risk mutations dominate outcomes following HCT.
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