Differentiating donor age on AML patient outcomes in the post-transplant cyclophosphamide contemporary era.

6564 Background: alloHCT provides curative potential for patients with AML. PTCy GVHD prophylaxis has changed this paradigm. Impact of donor age is unknown in the PTCy era. Methods: Utilizing the publicly available CIBMTR dataset, de-identified AML patients receiving alloHCT between 2017-2021 with PTCy-based GVHD prophylaxis were identified. Patients with primary induction failure or relapsed disease status at time of transplant were excluded. The main effect of donor age was examined across outcomes at 24-months. Univariate and multivariate analyses were performed. Results: 5,702 patients were included in the analysis. The median age at alloHCT was 59 years (IQR, 46-66). Median donor age was 33 years (IQR, 22-42). CI of relapse at 24 months was 36.4% (95% CI, 33.1%-39.8%) for donors aged ≥45 years (yrs), 32.9% (95% CI, 24.6%-41.2%) for donors aged 0-19 yrs, 30.5% (95% CI, 28.6%-32.4%) for donors aged 20-34 yrs, and 30.1% (95% CI, 27.3%-32.9%) for donors aged 35-44 yrs; p=0.003 (Gray's test). Overall survival (OS) at 24 months was 45.9% (95% CI, 42.6%-49.6%) for donors aged ≥45 yrs, 55.4% (95% CI, 47.1%-65.2%) for donors aged 0-19 yrs, 58.5% (95% CI, 56.5%-60.6%) for donors aged 20-34 yrs, and 53.3% (95% CI, 50.3%-56.5%) for donors aged 35-44 yrs; p<0.001. Leukemia-free survival at 24 months was 39.4% (95% CI, 36.2%-43.0%) for donors aged ≥45 yrs, 48.2% (95% CI, 40.1%-57.9%) for donors aged 0-19 yrs, 51.4% (95% CI, 49.4%-53.5%) for donors aged 20-34 yrs, and 49.2% (95% CI, 46.2%-52.4%) for donors aged 35-44 yrs; p<0.001. In multivariable analysis, as compared to donor age >45, the 2 younger age groups, age 20-34 years (HR 0.41, 95%CI, 0.69-0.87; p=.004) and 35-44 years (HR 0.78, 95%CI, 0.66-0.92; p=.004) were independently associated with reduced relapse and superior LFS (HR 0.77, 95% CI, 0.69-0.87;p<.001) and (HR 0.77, 95% CI, 0.68-0.87; p<.001) respectively, and OS (HR 0.76, 95%CI, 0.67-0.86; p<.001) and (HR 0.80, 95% CI, 0.70-0.91; p<.001) respectively. In contrast, there was no significant difference between outcomes when the donor belonged to the age group 0-19 for relapse (HR 0.87, 95%CI, 0.61-1.22;p=.410, LFS (HR 0.84,95% CI, 0.65-1.09);p=.188), and OS (HR 0.79, 95%CI, 0.60-1.05;p=.108) (Table 1). Conclusions: In this homogeneous analysis, patients with AML undergoing PTCy-based GVHD prophylaxis in the contemporary era, younger donor between age groups 20-44 years conferred a significantly reduced relapse risk and superior LFS and OS. The findings inform optimal donor selection. Multivariate analyses (ref: donor age ≥45). Donor age 0-19 P 20-34 P 35-44 P OS 0.79 (0.60-1.05) 0.108 0.76 (0.67-0.86) <0.001 0.80 (0.70-0.91) <0.001 LFS 0.84 (0.65-1.09) 0.188 0.77 (0.69-0.87) <0.001 0.77 (0.68-0.87) <0.001 Relapse 0.87 (0.61-1.22) 0.410 0.81 (0.69-0.93) 0.004 0.78 (0.66-0.92) 0.004 Adjusted for donor age, year of transplant, DRI, year of HCT, donor type, graft type, conditioning intensity, and ethnicity.