Second Allogeneic Hematopoietic Cell Transplantation for Relapsed Adult Acute Myeloid Leukemia: Outcomes and Prognostic Factors

Second allogeneic hematopoietic cell transplantation (HCT2) is potentially curative for adults with acute myeloid leukemia (AML) or myelodysplastic neoplasm (MDS)/AML experiencing relapse after a first allograft (HCT1), but prognostic factors for outcomes are poorly characterized. To provide a detailed analysis of HCT2 outcomes and associated prognostic factors in a large single-center cohort, with a focus on identifying predictors of relapse and nonrelapse mortality (NRM), we studied adults >= 18 years who underwent HCT2 at a single institution between April 2006 and June 2022 for relapsed AML (n = 73) or MDS/AML (n = 8). With a median follow-up among survivors of 74.0 (range: 10.4 to 187.3) months, there were 30 relapses and 57 deaths, of which 29 were NRM events, contributing to the estimates for relapse, overall survival (OS), relapse-free survival (RFS), and NRM. Three-year estimates for relapse, RFS, and OS were 37% (95% confidence interval: 27% to 48%), 32% (23% to 44%), and 35% (26% to 47%). The rate of NRM at 100 days and 18 months was 20% (12% to 29%) and 28% (19% to 39%). Outcomes differed markedly across patient subsets and were substantially worse for patients who underwent HCT2 with active disease (ie, morphologic evidence of bone marrow and/or extramedullary disease), for patients who relapsed <= 6 months after HCT1, and for patients with higher HCT-specific Comorbidity Index (HCT-CI) or treatment-related mortality (TRM) scores. After multivariable adjustment, active disease was associated with a higher risk of relapse (hazard ratio [HR] = 3.19, P = .006) and shorter RFS (HR = 2.41, P = .008) as well as OS (HR = 2.17, P = .027) compared to transplant in morphologic remission without multiparameter flow cytometric evidence of measurable residual disease. Similarly, a relapse-free interval <= 6 months after the first allograft was associated with higher risk of relapse (HR = 5.86, P < .001) and shorter RFS (HR = 2.86; P = .001) and OS (HR = 2.45, P = .003). Additionally, a high HCT-CI score was associated with increased NRM (HR = 4.30, P = .035), and shorter RFS (HR = 3.87, P = .003) and OS (HR = 3.74, P = .006). Likewise, higher TRM scores were associated with increased risk of relapse (HR = 2.27; P = .024) and NRM (HR = 2.01, P = .001), and inferior RFS (HR = 1.90 P = .001) and OS (HR = 1.88, P = .001). A significant subset of patients with AML or MDS/AML relapse after HCT1 are alive and leukemia-free 3 years after undergoing HCT2. Our study identifies active leukemia at the time of HCT2 and early relapse after HCT1 as major adverse prognostic factors, highlighting patient subsets in particular need of novel therapeutic approaches, and supports the use of the HCT-CI and TRM scores for outcome prognostication.