Haploidentical transplantation with post-transplant cyclophosphamide is not inferior to 9/10-MUD transplantation with ATG in patients with myeloid malignancies.

The selection of the best available donor is crucial for patients' outcome after allogeneic stem cell transplantation (allo-SCT). In the absence of fully Human leucocyte antigen (HLA) -matched donors, mismatched unrelated donor (9/10-MUD) or haploidentical donor (haplo) can be considered. No consensus has been reached on the best alternative and large real-world data are warranted to support decisional processes. We compared the outcome of 1413 patients with myeloid malignancies undergoing allo-SCT from 9/10-MUD with anti-thymocyte-globulin (ATG) (n = 1134) or haplo with post-transplant cyclophosphamide (PT-Cy, n = 279) between 2009 and 2020 in 48 German centres. Donor type with related graft versus host disease (GvHD) prophylaxis showed in multivariable analysis no significant impact on acute GvHD development, both grade II-IV (HR 0.90, 95% CI 0.69-1.19, p = 0.469) and severe (HR 1.22, 95% CI 0.82-1.81, p = 0.319), nor on moderate to severe chronic GvHD (HR 0.78, 95% CI 0.59-1.03, p = 0.077). Moreover, no influence from donor type was observed on GVHD-relapse-free survival (HR 1.12, 95% CI 0.92-1.36, p = 0.227), progression-free survival (HR 1.2, 95% CI 0.95-1.51, p = 0.121), non-relapse mortality (HR 1.1, 95% CI 0.81-1.51, p = 0.542) and overall survival (HR 1.16, 95% CI 0.91-1.48, p = 0.235). Our real-world data demonstrate that haplo allo-SCT with PT-Cy is not inferior to 9/10-MUD allo-SCT with ATG.