LAUSR

Optimal donor selection is fundamental to successful allogeneic hematopoietic cell transplantation (HCT), and donor age influences survival after both matched unrelated donor (MUD) and haploidentical donor HCT. Though recent studies have shown similar outcomes between MUD and haploidentical HCT, it is unknown if outcomes differ following HCT with younger haploidentical donors compared to HCT with older MUDs. Therefore, we performed a retrospective analysis comparing outcomes of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) patients who underwent HCT with younger (≤35 years) haploidentical donors (n = 494) or older (>35 years) MUDs (n = 1005). Patients in the haploidentical and MUD groups received post‐transplant cyclophosphamide (PTCy) and conventional graft‐versus‐host‐disease (GVHD) prophylaxis, respectively. In multivariate analysis, use of younger haploidentical donors was associated with improved overall survival (hazard ratio [HR] 0.81, 95% confidence interval [CI] 0.69–0.95, p = .01) and lower rates of grade II‐IV acute GVHD (HR 0.64, 95% CI 0.53–0.77, p < .001), grade III‐IV acute GVHD (HR 0.37, 95% CI 0.25–0.53, p < .001), and chronic GVHD (HR 0.49, 95% CI 0.40–0.60, p < .001). Relapse rates were similar among those who received myeloablative conditioning but were higher in patients of the younger haploidentical group who received reduced intensity conditioning (HR 1.49, 95%CI 1.18–1.88, p = .001). The younger haploidentical group had significantly lower non‐relapse mortality ≥3 months post‐HCT (HR 0.59, 95% CI 0.38–0.90, p = .02). Our data support the use of younger haploidentical donors with PTCy over older MUDs with conventional prophylaxis in patients with MDS or AML. Further studies on the importance of donor age in haploidentical and MUD HCT with PTCy prophylaxis are warranted.