Late outcomes after posttransplant cyclophosphamide–based GVHD prophylaxis in patients with AML: an ALWP-EBMT study

• HLA matching did not impact late transplant outcomes after PT-Cy-based GvHD prophylaxis. • Older donor age and female-to-male donor-recipient sex mismatch were associated with increased late NRM. Data on late events following allogeneic hematopoietic stem cell transplantation (allo-HSCT) with post-transplant cyclophosphamide (PT-Cy)-based graft-versus-host disease (GvHD) prophylaxis in patients with acute myeloid leukemia (AML) remain very limited. We analyzed long-term outcomes in 1,289 patients from the EBMT registry who underwent PT-Cy-based allo-HSCT for AML in first remission from haploidentical (haplo, n=906), 10/10 matched unrelated (MUD, n=208), or matched sibling donors (MSD, n=175), and who remained leukemia-free 2 years post-transplant. At 2 years from the landmark, the cumulative incidence of relapse and non-relapse mortality (NRM) were 6% and 4% in haplo, 7% and 3% in MUD, and 8% and 4% in MSD recipients, respectively. Similarly, 2-year estimates of leukemia-free survival (LFS) and overall survival (OS) were 91% and 93% for haplo, 90% and 95% for MUD, and 88% and 93% for MSD recipients, respectively. No statistically significant association was found between donor type and long-term transplant outcomes. In contrast, transplantation from a female donor to a male recipient (hazard ratio [HR]: 2.70, p=0.013) and older donor age (HR per 10-year increase: 1.34, p=0.036) were associated with increased risk of late NRM. These associations were confirmed in subanalyses in the haploidentical cohort. Notably, no factors associated with late relapse were identified in the multivariable models. PT-Cy-based allo-HSCT is associated with favorable outcomes in AML patients who remain leukemia-free 2 years after transplant. Long-term outcomes after haploidentical allo-HSCT were comparable to those of 10/10 MUD or MSD recipients in the setting of PT-Cy GvHD prophylaxis.