Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 18 3 2024 07 18 227 239 Murat Yıldırım Gülhane Educational and Research Hospital, Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye Selim Sayın Gülhane Educational and Research Hospital, Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye Melda Cömert Gülhane Educational and Research Hospital, Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye Esra Şafak, Yılmaz Gülhane Educational and Research Hospital, Department of Medical Informatics, Ankara, Turkiye Ferit Avcu Ankara Memorial Hospital Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye Ali Ural Bayındır Sögütözü Hospital Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye Meltem Aylı Gülhane Educational and Research Hospital, Department of Hematology and Bone Barrow Transplantation Unit, Ankara, Turkiye 2023 03 29 2023 12 28 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. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/2005 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/2005/1037