Improved Post-Transplant Outcomes in Recent Years for AML Patients with Intermediate Karyotype, FLT3-ITD and Wild Type NPM1: A Report from the EBMT Acute Leukemia Working Party

Rationale: Allogeneic hematopoietic cell transplantation (allo-HCT) is recommended in first complete remission (CR1) in acute myeloid leukemia (AML) patients harboring FLT3 internal tandem duplication (FLT3-ITD). However, historically, long-term survival has been poor due to early relapse, particularly for patients with wild-type NPM1. Recently, FLT3 inhibitors in combination with chemotherapy before allo-HCT, or as post-transplant maintenance, have significantly reduced the risk of relapse and improved survival. Here, we assessed real-world changes over time in transplant characteristics and post-transplant outcomes in young AML patients with FLT3 ITD and either NPM-1 mutated or wild type, using a large dataset from the European Society of Blood and Marrow Transplantation (EBMT) registry. Patients and Methods: We identified 1827 adult AML patients (54% female; median age 49 years, range 18-60) with FLT3 ITD, intermediate karyotype and available NPM1 mutation status, allografted between 2012 and 2021 in CR1 from a matched related (32%), matched unrelated (56%) or haploidentical donor (12%). NPM1 was mutated in 72% of patients. At transplant, 834 patients were measurable residual disease (MRD) positive, 464 MRD negative, and 529 were not evaluated or missing. Comorbidity index (CI) was zero in 59% of patients with available data. Conditioning was myeloablative (MAC) in 64% of patients. In vivo T cell depletion (TCD) graft was given to 62% of patients, post-transplant cyclophosphamide (PTCy) to 17%, and 87% received peripheral blood stem cells (PBSC). Most patients (66%) and donors (54%) were cytomegalovirus (CMV) positive. Median follow-up of alive patients was 30 months (IQR 28-32). Results: We compared changes in patient and transplant characteristics over time in 688 (38%) patients transplanted between 2012 and 2016 and 1139 (62%) patients transplanted between 2017 and 2021. Patients transplanted in recent years had a shorter follow up, were more likely to have NPM1 mutation, to be MRD positive, to have a higher CI, to receive a transplant from a haploidentical donor, a CMV positive donor, and to receive PBSC and PTCy. For patients with wild-type NPM1, day 100 acute graft-versus-host disease (GVHD) grade II-IV and grade III-IV were encountered in 29% and 11% of patients transplanted in 2021-2016, respectively, and 21% and 7% for patients transplanted in 2017-2021, respectively. The 2-year cumulative incidence of chronic and extensive chronic GVHD were 32% and 16%, respectively for 2012-2016 and 36% and 20%, respectively for 2017-2021. Over time, the 2-year cumulative incidence of relapse (CIR) significantly decreased from 43% to 31% between the two time periods (p<0.04) and non-relapse mortality (NRM) significantly decreased from 14% to 8% (p<0.05). The 2-year leukemia free survival (LFS) and overall survival (OS) significantly improved over time from 54% to 64% (p<0.02) and from 63% to 71% (p<0.05) respectively, whereas GVHD-free, relapse-free survival (GRFS) improved from 39% to 46% (p=0.08). In multivariate Cox analysis (MVA), transplantation in recent years significantly reduced the CIR (hazard ratio [HR]=0.65; p<0.01), and acute GVHD grade II-IV (HR=0.6; p<0.01) and significantly improved LFS (HR=0.67; p=0.02), OS (HR=0.66; p<0.03), and GRFS (HR=0.77; p<0.05). The use of unrelated donors increased the risk of acute GVHD but reduced the CIR whereas the use of haploidentical donors increased NRM. In vivo TCD reduced the risk of chronic GVHD whereas female donors to male recipients increased it. PTCy decreased the risk of NRM whereas MAC reduced the CIR. For patients with NPM1 mutation, no significant changes over time in post-transplant outcomes were noted except for decreased NRM from 15% for 217 patients transplanted in 2012-2016, to 10% for 288 patients transplanted in 2017-2021 (p<0.02). In MVA, transplantation in recent years did not significantly affect any of the post-transplant outcomes. Conclusion: In AML patients with FLT3 ITD and wild-type NPM1, we noticed a significant decrease over time in the CIR and a significant improvement of LFS, OS and GRFS, likely reflecting the efficacy of FLT-3 inhibitors, including when used as post-transplant maintenance, in this high-risk setting. On the contrary, no significant change over time was noticed in post-transplant outcomes of patients harboring NPM1 mutation.