Comparison of Cyclophosphamide-Based Graft Versus Host Disease Prophylaxis after Allogeneic Stem Cell Transplantation from 9/10 HLA Matched Unrelated Donor with Standard Graft Versus Host Disease Prophylaxis after 10/10 HLA Matched Relative Donor Tr

Background: Graft Versus Host Disease (GvHD), which can be observed at a rate of 30-80% after allogeneic stem cell transplantation (ASCT) is an important complication that adversely affects the survival and quality of the life of patients. Posttransplant cyclophosphamide (PTCy) effectively prevents GvHD after HLA-haploidentical ASCT. In our study, the use of PTCy in 1-antigen HLA-mismatched unrelated donor (9/10MMUD) ASCT was compared with standard GvHD prophylaxis in HLA-identical related donor (MRD) ASCT. Materials and Methods: We conducted a retrospective study of the comparison of 42 patients with 9/10 MMUD ASCT receiving PTCy+Methotrexate (MTX)+Calcineurin Inhibitor (CNI) and 37 patients with HLA-identical MRD who received MTX+CNI  in 3 bone marrow transplantation centers.  Results: Cumulative incidences of grade I-II (64.6% vs 45.4%, p=0.187) or grade III to IV acute GvHD (35.4% vs54.6%, p=0.187) and chronic GvHD (11.9% vs 29.7%, p=0.096) were similar in the PTCy group and control group. No statistically significant differences were observed between PTCy and the control group in overall survival rate (52.4% vs 62.2%, p=0.381), progression-free survival (1483.97 vs 1200.70 days, p=0.502), relapsed-related mortality rate (21.4% vs 16.2%, p=0.556) and treatment-related mortality rate (16.7% vs 21.6%, p=0.575). Conclusion: With the addition of PTCy to standard GvHD prophylaxis in 9/10MMUD ASCT, the risk of GvHD due to incompatibility and unrelated transplantation is eliminated, and transplantation success is achieved with MRD ASCT. PTCy-based prophylaxis is an effective and safe strategy to prevent GvHD in 9/10 MMUD ASCT without increasing the risk of relapse and treatment-related mortality.