Allogeneic hematopoietic cell transplantation for acute leukemia patients not in complete remission.

6553 Background: Current guidelines support allogeneic hematopoietic cell transplantation (allo-HCT) in patients with acute leukemia who achieve complete remission (CR) and are at high risk for relapse. Patients with primary refractory disease or those refractory to re-induction therapy after relapse have a poor prognosis without allo-HCT. While several studies have explored the role of allo-HCT in this setting, most have focused on patients receiving myeloablative conditioning (MAC) and have not included contemporary transplant patients or accounted for the impact of molecular genetic risk factors. Consequently, the benefit of allo-HCT in this patient population remains unclear. Methods: This study evaluated the outcomes of patients with acute leukemia from two centers who underwent allo-HCT between 2009 and 2020 while not in CR at the time of transplant, receiving either myeloablative conditioning (MAC) or reduced-intensity conditioning (RIC) regimens. Results: Our cohort included 196 patients who underwent transplantation between 2009 and 2020, with the majority (86%) diagnosed with acute myeloid leukemia (AML). At 36 months post-transplant, the probability of overall survival (OS) was 24% (95% CI: 19-31). In multivariable analysis, the presence of circulating blasts, recipient CMV seropositivity, and low pre-transplant albumin levels were associated with reduced OS. The cumulative incidence of relapse was 54% (95% CI: 47-61) at 36 months, with the presence of circulating blasts being significantly associated with an increased incidence of relapse. Among AML patients, the presence of at least one high-risk mutation (TP53, RUNX1, ASXL1, or FLT3-ITD, historically considered high-risk per National Comprehensive Cancer Network [NCCN] criteria version 3.2021) was also associated with an increased incidence of relapse. Conclusions: Allo-HCT provides a durable remission in a select group of patients with relapsed or refractory acute leukemia, with an overall survival of 24% at 36 months. The presence of circulating blasts, CMV seropositivity, and low albumin levels at the time of allo-HCT were associated with increased relapse and inferior OS in this retrospective analysis. The impact of these factors should be further investigated in larger, prospective cohorts to better identify patients with acute leukemia not in CR who would benefit from allo-HSCT.