Impact of Donor Type on Outcomes After Allogeneic Hematopoietic Cell Transplantation in Myelofibrosis: A Study on Behalf of the Chronic Malignancies Working Party of the EBMT

Selecting the optimal donor is crucial for optimizing results of allogeneic hematopoietic cell transplantation (allo‐HCT). We analyzed outcomes based on donor type in 2809 myelofibrosis (MF) patients undergoing first allo‐HCT between 2015 and 2021 at EBMT centers. Study outcomes included overall survival (OS), progression‐free survival (PFS), relapse, non‐relapse mortality (NRM), engraftment, and graft‐versus‐host disease (GvHD). Four groups were compared: matched sibling donor (MSD, n = 742), matched unrelated donor (MUD, n = 1401), mismatched unrelated donor (MMUD, n = 379) and haploidentical donor (HD, n = 287). After a median follow‐up of 33.5 months, 3‐year OS rates were 65.8%, 61.5%, 53.2%, and 57.7% for MSD, MUD, MMUD, and HD, respectively. Multivariable analyses (MSD as reference) showed that donor type significantly correlated with OS (HR: 1.63 for MMUD, HR: 1.42 for HD), PFS (HR: 1.38 for MMUD), NRM (HR: 1.73 for MMUD, HR: 1.47 for HD), engraftment (HR: 0.72 for MMUD, HR: 0.40 for HD), grade 2–4 acute GvHD (HR: 1.53 for MUD, HR: 1.69 for MMUD, HR: 1.49 for HD), and extensive chronic GvHD (HR: 0.77 for MUD, HR: 0.65 for HD). Donor type was not associated with relapse risk. In patients over 60 years, correlations between donor type and outcomes were consistent with those in the overall study population. In summary, with current practices, MF patients receiving MSD or MUD grafts achieve comparable outcomes. In contrast, MMUD and HD transplants have worse OS due to increased NRM. MMUD transplants have a higher risk of GvHD than HD transplants, but this difference seems to disappear with post‐transplant cyclophosphamide.