Impact of NPM1/FLT3-ITD genotypes defined by the2017 European LeukemiaNet in patients with acute myeloid leukemia

Patients with AML harboring FLT3 internal tandem duplications (ITD) have poor outcomes, in particular AML with a high (greater than or equal to0.5) mutant-to-wildtype allelic ratio (AR). The 2017 European LeukemiaNet (ELN) recommendations defined four distinct FLT3-ITD genotypes based on the ITD-AR and the NPM1 mutational status. In this retrospective, exploratory study, we investigated the prognostic and predictive impact of the NPM1/FLT3-ITD genotypes categorized according to the 2017 ELN risk groups in patients randomized within the RATIFY trial evaluating the addition of midostaurin to standard chemotherapy. The four NPM1/FLT3-ITD genotypes significantly differed with regard to clinical and concurrent genetic features. Complete ELN risk categorization could be done in 318 of 549 trial patients with FLT3-ITD AML. Significant factors for response after one or two induction cycles were ELN risk group and white blood cell (WBC) counts; treatment with midostaurin had no influence. Overall survival (OS) differed significantly between ELN risk groups with estimated 5-year OS probabilities of 0.63, 0.43, and 0.33 for favorable-, intermediate- and adverse-risk groups, respectively (P<0.001). Multivariate Cox model for OS using allogeneic hematopoietic-cell transplantation (HCT) in first complete remission as a time-dependent variable revealed treatment with midostaurin, allogeneic HCT, ELN favorable-risk group, and lower WBC counts as significant favorable factors. In this model, there was a consistent beneficial effect of midostaurin across ELN risk groups.