PF256 RATIFY: PROGNOSTIC IMPACT OF FLT3 TYROSINE KINASE DOMAIN (TKD) AND NPM1 MUTATION STATUS IN PATIENTS WITH NEWLY DIAGNOSED ACUTE MYELOID LEUKEMIA (AML) TREATED WITH MIDOSTAURIN + STANDARD CHEMOTHERAPY
Authors: M.T. Voso, R.A. Larson, T. Prior, G. Marcucci, D. Jones, J. Krauter, M. Heuser, S. Lavorgna, J. Nomdedeu, S.M. Geyer, R. Klisovic, A.H. Wei, J. Sierra, M.A. Sanz, J.M. Brandwein, T.M. de Witte, J.H. Jansen, D. Niederweiser, F.R. Appelbaum, B.C. Medeiros, M.S. Tallman, R.F. Schlenk, A. Ganser, S. Amadori, Y. Cheng, Y. Chen, E. Tiecke, L. Du, G. Ehninger, C. Thiede, K. Döhner, H. Döhner, R.M. Stone, C.D. Bloomfield, F. Lo‐Coco
Journal: HemaSphere (2019)

Background: Mutations localized in the tyrosine kinase domain activation loop of FLT3 (FLT3‐TKD), induce constitutive tyrosine phosphorylation, and activation of the receptor tyrosine kinase similarly to FLT3 internal tandem duplication (ITD) mutations. However, the prognostic role of FLT3‐ TKD in AML is not well established. In the phase 3 RATIFY trial [CALGB 10603/Alliance; NCT00651261; Stone et al. N Engl J Med. 2017] midostaurin, in combination with standard chemotherapy, improved survival outcomes across all three FLT3 stratification subgroups (ITD high allelic ratio (AR) [≥ 0.7], ITD low AR [&lt; 0.7] and TKD) vs placebo. Aims: Here, a post hoc analysis was used to establish the efficacy of midostaurin in patients (pts) in the RATIFY trial stratified by FLT3 ‐TKD AR and NPM1 mutational status. Methods: In RATIFY, newly diagnosed pts with AML 18–60 years (y) old were randomly assigned to receive midostaurin or placebo together with standard induction and consolidation therapy followed by twelve 28‐day cycles of maintenance therapy with midostaurin or placebo. FLT3 ‐TKD mutation was detected by PCR and capillary electrophoresis at nine reference laboratories. The FLT3 ‐TKD AR was calculated as the ratio between the areas under the curve of mutant to wild‐type allele. Pts were categorized as NPM1 mutated (mut) or NPM1 wild‐type (WT) using PCR. Efficacy outcomes included complete remission (CR), overall survival (OS), event‐free survival (EFS) and disease‐free survival (DFS). EFS and DFS analyses were performed considering CR within a 60‐day window. P values presented were not adjusted for multiplicity. Results: Of 163 FLT3 ‐TKD pts, 134 with available NPM1 data had consented for exploratory analysis and were included in this study. Overall, 58.9% of pts had NPM1 ‐mut, 47.8% were male and the median age was 49 y (range: 19.3–59.9 y). The median white blood cell (WBC) count was higher in pts with NPM1 ‐mut than in pts with NPM1 ‐WT (34.1 vs 15.5 × 10 9 /L). The median FLT3 ‐TKD AR was 0.4 (range: 0–2.7). Overall CR rate (regardless of NPM1 genotype) was 64% for midostaurin and 56% for placebo in FLT3 ‐TKD pts. Pts with FLT3 ‐TKD AR ≥ 0.4 treated with midostaurin showed a trend towards improved OS and reduced cumulative incidence of relapse (CIR) (Figure). In FLT3 ‐TKD AR ≥ 0.4 pts, the presence of a NPM1 mutation had a significant prognostic effect for all endpoints consistently with hazard ratios (HRs) around 0.50 or lower. Regardless of treatment OS, EFS, and DFS estimates at 3 y were 73% vs 52%, 48% vs 25%, and 74% vs 47%, respectively, for the 45 pts with FLT3 ‐TKD/ NPM1 ‐mut vs the 25 pts with FLT3 ‐TKD/ NPM1 ‐WT. It should be noted that the number of pts in each subgroup was small. Multivariate analyses in these FLT3 ‐TKD pts revealed that NPM1 genotype was an independent prognostic factor for OS and EFS (2‐sided P &lt; 0.05), whereas study drug, age, sex, TKD AR, WBC at baseline and stem cell transplantation (SCT) (no/yes) did not reach this level of significance in the Cox model. Summary/Conclusion: This post hoc analysis of the subset of FLT3 ‐TKD pts in the RATIFY trial showed the high prognostic value of NPM1 mutational status. Midostaurin showed an overall benefit in the FLT3 ‐TKD pts for OS, EFS, CR and DFS, with the impact of treatment on outcome for NPM1 ‐mut pts being greatest in those with higher FLT3 ‐TKD allelic burden. U10CA180821, U10CA180882, U24CA196171, U10CA180861; Novartis; htt∗∗∗ps://acknowledgments.alliancefound.org image