Relapse after allogeneic hematopoietic stem cell transplantation in patients with active acute myeloid leukemia

Relapse treatment after allogeneic hematopoietic cell transplantation (HCT) for acute myeloid leukemia (AML) remains challenging. This retrospective single-center study investigates outcomes of AML patients transplanted with active disease who experienced relapse after HCT. We analyzed 67 patients who relapsed after HCT between 2014 and 2024. Patients were classified as having impending molecular relapse (n = 42, defined by persistent or recurrent genetic aberrations and/or a drop in CD34 + donor chimerism < 95 %) or overt hematologic relapse (n = 25). We evaluated overall survival (OS), relapse-free survival (RFS), and responses to relapse treatments. Thirty-seven (88 %) patients with impending relapse had a decrease in CD34⁺ donor chimerism; and only 5 (12 %) patients harbored an impending relapse without decrease in CD34⁺ donor chimerism. Two-year OS with impending relapse was 45 % (95 % confidence interval [CI], 31-64 %), with 13 of 23 patients (57 %) achieving measurable residual disease (MRD) negative remissions after donor lymphocyte infusions (DLI). RFS was significantly shorter in patients with impending relapse who did not receive DLI (hazard ratio [HR] 3.23, 95 % CI, 1.22-8.33, P = .02), whereas OS did not differ (HR 2.00, 95 % CI, 0.66-5.88; P = 0.22). Patients with overt relapse had poor outcomes with a 1-year survival of 24 % (95 % CI, 12-48 %). Our data underscore the importance of close follow-up after transplantation, especially in high-risk AML. Whenever relapse is imminent, timely immune-based therapy may induce durable MRD-negative remissions and was associated with improved RFS compared to hypomethylating agents without DLI in our cohort.