P153 | POST-TRANSPLANT CYCLOPHOSPHAMIDE-BASED GVHD PROPHYLAXIS IN MISMATCHED UNRELATED DONORS: A REAL-LIFE RETROSPECTIVE SINGLE CENTER ANALYSIS.

In large registry analysis and prospective studies, post-transplant cyclophosphamide (PTCY) as graft-versus-host-disease (GVHD) prophylaxis led to encouraging outcome in patients receiving transplantation from mismatched unrelated donors (mMUD). In this single center cohort, we describe the results obtained using PTCY in mMUD compared to prophylaxis with anti-lymphocyte globulins (ATG). From 2010 to 2024, 54 patients were transplanted with mMUD. Until 2020, GVHD prophylaxis was with ATG (day -2 and -1, dose 2.5 or 3.5/kg), cyclosporine A (CyA), and short course methotrexate (ATG-group, n= 32), while from 2021, patients received PTCY (40-50 mg/kg, day +3 and +4), CyA, and micofenolate mofetil (PTCY-group, n= 22). Comparison of continuous non parametric variables we used Mann Whitney test. For overall survival analysis we used Kaplan Maier estimates and Log-Rank test. For comparison of categorical variables chi squared test was used. For survival analysis we used CI estimates and Gray’s test. For all statistical analyses we used NCSS2019 software. Endpoints were overall survival (OS), progression free survival (PFS), cumulative incidence of acute GVHD, no-relapse mortality (NRM). 54 patients underwent transplantation from mMUD between 2010 to 2024. Patient characteristics and main results are described in Table 1. All patients received peripheral blood stem cell and engraftment rate was not statistically different between the 2 cohorts. In the whole cohort, 3-month (3M) cumulative incidence (CI) of grade 2-4 and 3-4 acute GVHD was 13% and 9%, respectively. 3M, 6M and 1-year NRM was 17%, 23%, and 36%, respectively. 1-year overall survival (OS) was 62%. Causes of death are indicated in Table 1. In PTCY-group vs ATG-group, CI grade 2-4 and 3-4 aGVHD was 10% vs 15% and 12%, respectively (p=0.85), 100-day, 6 months and 1 year NRM was 20% vs 15%, 20% vs 21% and 20% vs 42%, 1-y OS was 80% vs 54% (p=0.39), 1-y PFS was 64% vs 51% respectively (p=0.54). In univariate analysis, there was not statically differences between the 2 groups. In this small retrospective study, PTCY for mMUD transplantation was safe and effective with an acceptable rate of aGVHD. Comparison with ATG, PTCY shows a not significant trend to better OS, PFS and 1-y NRM.