Young unrelated donors confer a survival advantage for patients with myeloid malignancies compared to older siblings

Donor age is one factor to optimize allogeneic hematopoietic cell transplantation (alloHCT). Therefore, we investigated whether young unrelated donors (UD) provide a benefit for older patients with myeloid malignancies compared to HLA-identical sibling donors (MSD). We performed a retrospective registry study on patients ≥50 years who received a first alloHCT between 2010 and 2020. We compared event-free survival (EFS) of patients who were transplanted from MSD aged ≥50 years versus UD aged ≤35 years who were HLA-compatible for HLA-A, -B, -C, and -DRB1. In total, we analyzed data from 3460 patients. With multivariable adjustment EFS (HR 0.86, p = 0.003), OS (HR 0.82, p < 0.001), and risk of relapse (HR 0.84, p = 0.018) were significantly better for HLA-compatible UD compared to MSD. No survival advantage was found, when UD with unfavorable sex or CMV constellation were compared to MSD with favorable constellations. In a meta-analysis on 9905 patients with myeloid malignancies, including ours, we found reduced risk of relapse (pooled HR 0.78, p = 0.006) and better EFS (pooled HR 0.89, p < 0.001) for young matched UD versus MSD. To select young HLA-compatible UD over older MSD may reduce relapse risk and improve survival for older patients with myeloid malignancies.