P152 | IMPACT OF POST-TRANSPLANT CYCLOPHOSPHAMIDE IN PATIENTS UNDERGOING ALLOGENEIC TRANSPLANTATION FROM A HAPLOIDENTICAL DONOR, MUD OR MMUD. SINGLE-CENTER EXPERIENCE AT THE TRANSPLANT AND CELLULAR THERAPY CENTER, GOM, REGGIO CALABRIA

Background The introduction of post-transplant cyclophosphamide (PTCy) has improved outcomes in haploidentical hematopoietic stem cell transplantation (HSCT), reducing non-relapse mortality (NRM) and preventing graft-versus-host disease (GVHD). This approach has been extended to matched unrelated donor (MUD) and mismatched unrelated donor (MMUD) transplants, showing comparable effectiveness. Aims To analyze the outcomes of using PTCy in patients undergoing allogeneic HSCT from haploidentical, MUD, or MMUD donors. Methods We retrospectively analyzed 62 adult patients who underwent allogeneic HSCT between January 2020 and December 2024 at our center, C.T.M.O of Reggio Calabria, in order to assess firstly the incidence of GVHD and as a secondary objectives the overall survival (OS), NRM, relapse-free survival, GVHD)/relapse-free survival (GRFS). The overall patients characteristics at baseline are reported in table 1; 69.35% performed allogeneic HSCT from haploidentical donors, 4.8% from MUD, and 25.8% from MMUD (7/8 or 9/10 matches). The conditioning regimen was myeloablative (MAC) in 47 patients and reduced intensity (RIC) in 15. PTCy was administered at 40 mg/kg on days +3 and +4 for 15 patients (older or with high comorbidities) and at 50 mg/kg for the remaining 47. GVHD was assessed using the MAGIC criteria for acute and NIH 2014 for chronic cases. The median patient age was 54 years, with 13 patients over 65. Median follow-up was 18.2 months, and there were 17 deaths (27.4%). Complications included 44 infections (30 bacterial), 2 cases of veno-occlusive disease (VOD), and 2 atrial fibrillation episodes. Results At one year, OS was 75%, with a significant correlation to relapse (84% OS in non-relapsed vs. 40% in relapsed, p<0.001). Four-year OS was 63%, and RFS at one year was 79%. Relapse incidence at one year was 14%, and NRM was 17%. Acute GVHD occurred in 16% of cases, chronic GVHD in 19.4%, with a five-year chronic GVHD-free survival of 79%. GRFS at five years was 42%. Conclusions Despite the limitations of our study (retrospective, single-center, no ATG control group, small and heterogeneous sample), PTCy proved to be a safe and effective GVHD prophylaxis strategy in patients undergoing allo-HSCT from haploidentical, MUDs and MMUDs donors. It was well tolerated in all age groups, including elderly patients, without increased toxicity or mortality. In addition, lower doses of PTCY did not adversely affect outcomes, supporting its flexible use.