Comparing myeloablative and reduced-intensity conditioning for allogeneic PBSCT in MDS with increased blasts.

e18573 Background: Myelodysplastic syndrome with increased blasts (MDS-IB) is a complex hematologic malignancy characterized by ineffective hematopoiesis and a high risk of transformation to acute myeloid leukemia (AML). Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a potentially curative treatment option for these patients, but the optimal conditioning regimen remains a subject of ongoing debate. This retrospective study aims to compare the outcomes of patients with MDS-IB who underwent allogeneic peripheral blood stem cell transplantation (PBSCT) using either MAC or RIC regimens between 2015 and 2023. Methods: We identified 53 patients with MDS-IB1 and MDS-IB2 who underwent allogeneic PBSCT. They received MAC (FBT or FB4) with fludarabine 50 mg/m2/day, day -6 to day -2, busulfan 3.2 mg/kg/day, day -5 to day -2, +/- TBI 200 cGy/day on day -1 and day 0. Or reduced intensity conditioning (FB2) with fludarabine 30 mg/m2/day day -6 to day -2, busulfan 3.2 mg/kg/day day -3 and day -2. The endpoints were progression-free survival (PFS) and overall survival (OS) at 2-years. Kaplan Meier method was used to study survival estimates, log-rank test was used to compare those estimates. Results: The median age at diagnosis was 63.8 years. Most patients had underlying MDS-IB2 (62%), and 79% of patients received their transplant from matched unrelated donors. Only 21% of patients received MAC with either FB4 or FBT, while the rest received RIC. The median follow-up was 9.7 months. 2-year PFS was 87.5% for the MAC group versus 48.9% for RIC group (p-value 0.099). The 2-year overall survival (OS) was 54.5% in the MAC group compared to 35.7% in the RIC (p-value = 0.737). Conclusions: Our institutional 2-year analysis showed a non-significant difference in PFS and OS between the conditioning regimens in MDS patients with increased blasts. This lack of statistical significance could be related to the small sample size and retrospective analysis. However, prospective review and multicenter analysis with a larger sample size may be warranted to validate the choice of conditioning regimen in this group of patients.