Analysis of Post-Transplant Clinical Outcomes and Prognostic Factors in FLT3-ITD Mutated Acute Myeloid Leukemia Patients Under ELN 2022 Risk Stratification

Background

In 2022 European LeukemiaNet (ELN) recommendations for diagnosis and management of acute myeloid leukemia (AML), one of the most important changes made to the genetic risk classification of AML is that the FLT3-ITD allelic ratio (AR) is no longer considered in the risk classification; consequently, AML with FLT3-ITD (without adverse-risk genetic lesions) are now categorized in the intermediate-risk group, irrespective of the allelic ratio or concurrent presence of NPM1 mutation.

Aims

To investigate the survival outcomes of FLT3-ITD mutated AML patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), based on prognostic stratification defined by the 2017 and 2022 ELN guidelines, and to analyze the risk factors affecting transplant prognosis.

Methods

A total of 163 FLT3-ITD mutated AML patients underwent allo-HSCT were enrolled in this study. Bone marrow aspirates were obtained, cytogenetic and molecular characteristics were collected at the time of diagnosis. Genetic risk category was classified according to the 2017 and 2022 edition of the European LeukemiaNet (ELN) recommendations. HLA-haploidentical donor transplants were performed if no HLA matched sibling or unrelated donor was available. Patients received myeloablative conditioning with a modified Bu/Cy/Flu/Ara-c (busulfan/cyclophosphamide/fludarabine/cytarabine) or MCBC (melphalan/cladribine/busulfan/cyclophosphamide) preparative regimen. The therapeutic process and clinical outcomes were retrospectively analyzed.

Results

We assessed 163 adults with FLT3-mutated AML (median age 37 years) allografted between 2017 and 2022 in our clinical center. The median follow-up of alive patients was 24.9 months. The 2-year relapse-free survival (RFS) and overall survival (OS) were 67.2% and 71.9%, respectively. The 2-year incidences of relapse and non-relapse mortality were 27.9% and 12.5%, respectively. There was no significant difference in survival outcomes between the intermediate and high-risk groups after transplantation, both defined by the 2017 and 2022 ELN guidelines. High FLT3-ITD allelic ratio (≥0.5) at initial diagnosis was associated with elevated WBC counts ( P<0.001), but did not affect the response ratefollowing induction chemotherapy ( P=0.059) . Patients with high allelic ratio were more likely to benefit from maintenance therapy after transplantation ( P=0.048 for OS). In univariate analysis, presence of NPM1 mutation and the allelic ratio of FLT3-ITD did not affect any of the transplant outcomes. In multivariate analysis, MRD-negative at transplantation, occurrence of chronic GVHD and posttransplant maintenance therapy improved OS and RFS.

Conclusion

Allo-HSCT can overcome the poor prognosis in patients with FLT3-ITD mutated AML. Neither the presence of NPM1 mutation nor the FLT3-ITD allelic ratio affected survival. Prevention of disease relapse after transplantation remains a challenge. The main prognostic factors affecting transplant outcomes included pre-transplant MRD status and the application of maintenance therapy. Thus, introduction of FLT3 inhibitors as post-transplant maintenance therapy and the development of highly sensitive MRD assays will further reduce disease recurrence and improve survival.