Abstract Background: Patients (pts) with AML harboring FLT3 -ITD mutations have poor outcomes. The higher relapse rate and inferior overall survival (OS) largely depend on the ITD mutant to wild-type (wt) allelic ratio. Furthermore, there is a strong gene-gene interaction between NPM1 mutation (NPM1 mut) and FLT3 -ITD. Consequently, the 2017 European LeukemiaNet (ELN) has included defined NPM1/FLT3- ITD genotypes for risk categorization. In the recent phase III RATIFY trial [NCT00651261; Stone et al., NEJM 2017] the addition of the multi-targeted kinase inhibitor midostaurin (M) to standard chemotherapy significantly prolonged OS and event-free survival (EFS) in pts with newly diagnosed AML and FLT3 mutation. Here, we evaluated the prognostic impact in a post-hoc analysis of the NPM1/FLT3 -ITD genotypes as defined by the 2017 ELN from randomized pts treated within the RATIFY trial. Study Design: In total, 428 of 717 pts were included who gave informed consent for biomarker analyses and who could be categorized to one of the 4 ELN NPM1 / FLT3 -ITD subgroups: NPM1 mut/ FLT3 -ITDlow (n=85), NPM1 mut/ FLT3 -ITDhigh (n=159), NPM1 wt/ FLT3 -ITDlow (n=75), and NPM1 wt/ FLT3 -ITDhigh (n=109) (allelic ratio: high, ≥0.5; low, Results: With regard to pts and disease characteristics, there was a higher proportion of female pts in the subsets with concurrent NPM1 mut, whereas higher white blood cell counts (WBC) and bone marrow blasts were found in the subsets with FLT3 -ITDhigh. Rates of complete remission (CR) positively correlated with NPM1 mut status, but not with FLT3 -ITD allelic ratio (p=.016). CR according to randomization only showed a trend in favor of M in NPM1 wt/ FLT3 -ITDlow pts (p=.058). OS was significantly different among the 4 groups (p=.001); median survival times were mo not reached (n.r.), 27 mo, 20 mo, and 17 mo for NPM1 mut/ FLT3 -ITDlow, NPM1 mut/ FLT3 -ITDhigh, NPM1 wt/ FLT3 -ITDlow, and NPM1 wt/ FLT3 -ITDhigh subgroups, respectively. This effect was even more pronounced when censoring pts at the time of allogeneic hematopoietic cell transplantation (alloHCT). OS according to randomization showed some differential effects of M among the 4 genotypes (Figure 1) with a significant beneficial effect of M in the NPM1 wt/ FLT3 -ITDhigh group (median OS 26 mo vs 14 mo for PBO; p=.025), whereas for the other genotypes beneficial effects of M did not reach statistical significance. OS analysis according to randomization censored at the time of alloHCT revealed an advantage of M for the NPM1 mut/ FLT3 -ITDlow (median n.r. in both arms; p=.038) and NPM1 mut/ FLT3 -ITDhigh (median, n.r. vs 18 mo for PBO; p=.032) subsets, while the significant effect present in the non-censored analysis for the NPM1 wt/ FLT3 -ITDhigh group was lost (median OS, 19 mo vs 17 mo for PBO; p=0.2). Similar to OS, non-censored EFS significantly differed among the 4 groups (p=.001); median EFS times were 16 mo, 8 mo, 4 mo, and 4 mo for the NPM1 mut/ FLT3 -ITDlow, NPM1 mut/ FLT3 -ITDhigh, NPM1 wt/ FLT3 -ITDlow, and NPM1 wt/ FLT3 -ITDhigh groups, respectively. EFS analysis according to randomization showed a beneficial effect of M in the NPM1 wt/ FLT3 -ITDhigh group (median EFS, 8 mo vs 3 mo for PBO; p=.016). Multivariable analysis including the 4 NPM1/FLT3 -ITD genotypes, treatment arm, sex, age, WBC and alloHCT revealed NPM1/FLT3 -ITD genotypes (OS: p Conclusions: Data from this large randomized trial suggest the high prognostic value of the NPM1/FLT3 -ITD genotypes considering the ITD mutant to wt allelic ratio. The study was not powered to show differential effects of M among genotypes; however, a beneficial effect of M on OS and EFS appeared most pronounced in the NPM1 wt/ FLT3 -ITDhigh group. Multivariate analysis revealed NPM1/FLT3 -ITD genotypes, treatment arm with M in favor to PBO, WBC, and alloHCT as independent prognostic factors for OS. KD and CT contributed equally Download : Download high-res image (306KB) Download : Download full-size image Disclosures Dohner: Novartis: Honoraria, Research Funding. Thiede: Roche: Consultancy; Bayer: Consultancy, Speakers Bureau; Agendix: Employment; Novartis: Consultancy, Speakers Bureau. Larson: Astellas: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Amgen Inc.: Research Funding. Jones: Novartis: Research Funding. Lo Coco: TEVA: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Lundbeck: Honoraria, Speakers Bureau. Wei: AbbVie, Celgene, Servier: Research Funding; AbbVie, Celgene, Novartis, Amgen, Servier: Membership on an entity's Board of Directors or advisory committees; AbbVie, Celgene, Novartis, Amgen, Servier: Honoraria. Cheng: Novartis: Employment, Other: stocks. Pallaud: Novartis Pharmaceuticals: Employment. Stone: DSMN: Consultancy; Sumitomo Dainippon: Consultancy; Roche: Consultancy; Pfizer: Consultancy; Ono: Consultancy; Novartis: Consultancy; Juno Therapeutics: Consultancy; Jazz,: Consultancy; Janssen: Consultancy; Cornerstone: Consultancy; Astellas: Consultancy; Amgen: Consultancy; Agios: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees. Dohner: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Arog Pharmaceuticals: Honoraria, Research Funding; Celator: Honoraria; Amgen: Honoraria; Agios: Honoraria; Sunesis: Honoraria; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Research Funding; Abbvie: Honoraria; Astex Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Research Funding; Pfizer: Research Funding; Seattle Genetics: Honoraria.