Prognostic Impact of Insertion Site in Acute Myeloid Leukemia (AML) with FLT3 Internal Tandem Duplication: Results from the Ratify Study (Alliance 10603)

Abstract Introduction: Internal tandem duplication of the FLT3 gene (FLT3-ITD), resulting in duplication of 3 to more than hundreds of nucleotides, are present in approximately 25% of adults with newly diagnosed AML. Several studies have shown that ITD mutations are associated with poor prognosis due to a high relapse rate, in particular in case of a high mutant to wild-type allele ratio and/or insertion site in the beta1-sheet of the tyrosine kinase domain-1 (beta1-sheet). Aims: To investigate the relationship between ITD insertion site and patient outcome, Roche 454 next generation sequencing (NGS) was performed in 452/555 (81.4%) FLT3-ITD positive patients (pts) enrolled into the RATIFY trial (NCT00651261). Results: NGS identified 908 ITDs with up to 9 ITDs per case (1 ITD: n=210, 46.5%; 2 ITDs: n=131, 29.0%; 3 ITDs: n=58, 12.8%; 4 ITDs: n=24, 5.3%; 5 ITDs: n=18, 4.0%; 6 ITDs: n=3, 0.7%; 7 ITDs: n=7, 1.5%; 9 ITDs: n=1, 0.2%). Median ITD-size was 45 nucleotides (range, 6-246); all ITDs were in-frame with direct head-to-tail orientation. According to the 4 functional groups, 488 ITDs (53.7%) were located within the juxtamembrane domain (JMD), 155 ITDs (17.1%) within the hinge region, 211 ITDs (23.2%) within the beta1-sheet, and 54 ITDs (5.9%) 3´of beta1-sheet. ITD size strongly correlated with insertion site, in that the more C-terminal the insertion site, the longer the size of the inserted fragment (P<.001). In 242 pts (53.5%) featuring multiple ITD clones, 698 concurrent integration sites were delineated, with coexistent integration sites within JMD being the most frequent interaction (37%) followed by JMD and beta1-sheet (13.5%), and within beta1-sheet (7.8%). NPM1 mutations (NPM1mut) were present in 203/358 pts (56.7%). Correlation of ITD insertion site with NPM1mut revealed a significantly lower incidence of NPM1mut in pts with insertion located within the hinge region (50/106, 47.2% vs 153/252, 60.7%; P=.02) and 3´of beta1-sheet (14/41, 34.1% vs 189/317, 59.6%; P=.002), whereas NPM1mut were significantly more frequent in pts with insertions affecting JMD (143/235, 60.9% vs 60/123, 48.8%; P=.03). Clinical characteristics differing among the 4 functional ITD groups were gender and WBC. Pts with insertions 3´of beta1-sheet were predominantly male (28/46, 60.9% vs 178/406, 43.8%; P=.03); pts with JMD insertions exhibited lower WBC (median 36.5 vs 52.7 x109/L; P=.03). Complete remission (CR) was achieved within 60 days in 248/452 pts (54.9%). To evaluate the impact of ITD insertion site on response to induction, a logistic regression model was used. ITD insertion sites were categorized in (i) only in beta1-sheet, (ii) in beta1-sheet and other sites, and (iii) outside the beta1-sheet. Other variables were ITD mutant to wild-type allelic ratio (fragment analysis, cutoff at 0.5), number of ITDs per patient, log2 of WBC counts, age, NPM1mut, and midostaurin treatment. In this model, only number of ITDs predicted lower CR rate (OR, 0.72; 95% CI, 0.57-0.90), while NPM1mut was a favorable marker for CR (OR, 2.69; 95% CI, 1.70-4.28). Median follow-up for survival was 60.6 months (mo); median event free survival (EFS) and overall survival (OS) were 3.9 mo and 24.4 mo, respectively. The 4-year EFS and OS rates were 21.0% (95% CI, 17.2%-24.8%) and 42.6% (95% CI, 37.9%-47.4%), respectively. Survival analysis according to categorized insertion site groups showed that pts exhibiting insertion exclusively in the beta1-sheet had significantly inferior OS (P=.014) compared to the other two groups. Multivariate models for OS and EFS including hematopoietic stem-cell transplantation (HSCT) as a time-dependent covariate revealed WBC counts as unfavorable and NPM1mut as favorable for both endpoints; further unfavorable factors were older age and exclusive insertion in the beta1-sheet (HR, 1.49; 95% CI, 1.01-2.20) for OS and number of ITDs (HR, 1.15; 95% CI, 1.04-1.28) for EFS; HSCT was a favorable factor only for EFS (HR, 0.66; 95% CI, 0.44-0.99). Midostaurin treatment was associated with in trend improved EFS (HR, 0.81; 95% CI, 0.63-1.03) and OS (HR, 0.77; 95% CI, 0.57-1.02). Conclusions: In this large cohort of 452 FLT3-ITD mutated AML treated within the RATIFY trial the negative prognostic impact of beta1-sheet insertion site of FLT3-ITD could be confirmed. Further analyses to investigate potential predictive effects of midostaurin treatment are ongoing. Support: U10CA180821, U10CA180882, U24CA196171, (CCSRI) #704970. Disclosures Du: Novartis: Employment. Gathmann:Novartis: Employment. Larson:Ariad/Takeda: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; BristolMyers Squibb: Consultancy, Research Funding. Medeiros:Celgene: Consultancy, Research Funding; Genentech: Employment. Tallman:Orsenix: Other: Advisory board; Cellerant: Research Funding; AROG: Research Funding; AbbVie: Research Funding; BioSight: Other: Advisory board; Daiichi-Sankyo: Other: Advisory board; ADC Therapeutics: Research Funding. Tiecke:Novartis: Employment. Pallaud:Novartis: Employment. de Witte:Amgen: Consultancy, Research Funding; Novartis: Research Funding; Celgene: Honoraria, Research Funding. Niederwieser:Novartis: Research Funding; Miltenyi: Speakers Bureau. Ehninger:Bayer: Research Funding; GEMoaB Monoclonals GmbH: Employment, Equity Ownership; Cellex Gesellschaft fuer Zellgewinnung mbH: Employment, Equity Ownership. Ganser:Novartis: Membership on an entity's Board of Directors or advisory committees. Bullinger:Bristol-Myers Squibb: Speakers Bureau; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Pfizer: Speakers Bureau; Bayer Oncology: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Speakers Bureau; Sanofi: Research Funding, Speakers Bureau. Döhner:Pfizer: Research Funding; Jazz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Sunesis: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Astellas: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; AROG Pharmaceuticals: Research Funding; Agios: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Pfizer: Research Funding. Thiede:Novartis: Honoraria, Research Funding; AgenDix: Other: Ownership.

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