Background: Somatic mutations in isocitrate dehydrogenase 1 (IDH1) occur in 6-10% of patients with acute myeloid leukemia (AML). Ivosidenib - an oral, potent inhibitor of the mutant IDH1 (mIDH1) enzyme - is FDA-approved for adults with relapsed/refractory m IDH1 AML and adults with newly diagnosed m IDH1 AML who are ≥ 75 years or have comorbidities that preclude use of intensive induction chemotherapy (IC). Data from a phase 1b study of 23 patients with newly diagnosed m IDH1 AML showed a favorable safety profile and encouraging clinical activity of ivosidenib + azacitidine (IVO+AZA; NCT02677922). Methods: In this global, double-blind, randomized, placebo-controlled, phase 3 study, patients were randomized 1:1 to IVO 500 mg once daily + AZA 75 mg/m 2 subcutaneously or intravenously for 7 days in 28-day cycles, or placebo + AZA (PBO+AZA), and stratified by region and de novo vs secondary AML. Key eligibility: untreated AML (WHO criteria), centrally confirmed m IDH1 status, not eligible for IC, ECOG 0-2. Primary endpoint: event-free survival (EFS; time from randomization until treatment failure, i.e. failure to achieve complete remission [CR] by week 24, relapse from remission, or death from any cause). Key secondary endpoints: CR rate, overall survival (OS), CR + CR with partial hematologic recovery (CRh) rate, and objective response rate (ORR). Results: From 19-Mar-2018 to 18-Mar-2021, 146 patients were randomized: 72 to IVO+AZA (median [interquartile range] age, 76.0 [70.5-79.5] years) and 74 to PBO+AZA (median [interquartile range] age, 75.5 [70.0-80.0] years). Fifty-four (75.0%) patients had de novo AML vs 18 (25.0%) with secondary AML in the IVO+AZA arm. Sixteen (22.2%) patients receiving IVO+AZA had poor-risk genetics per ELN guidelines vs 20 (27.0%) patients receiving PBO+AZA. Thirty-nine (26.7%) patients remain on treatment (27/72 patients in the IVO+AZA arm vs 12/74 patients in the PBO+AZA arm). EFS was statistically significant (HR = 0.33 [95% CI 0.16, 0.69]; P = 0.0011) in favor of the IVO+AZA arm. Median OS with IVO+AZA was 24.0 months vs 7.9 months with PBO+AZA (HR = 0.44 [95% CI 0.27, 0.73]; P = 0.0005). CR rate with IVO+AZA was 47.2% (34/72 patients; 95% CI 35.3%, 59.3%) vs 14.9% (11/74 patients; 95% CI 7.7%, 25.0%) with PBO+AZA (P < 0.0001). Median time to CR was 4.3 months with IVO+AZA vs 3.8 months with PBO+AZA. CR+CRh rate with IVO+AZA was 52.8% (38/72 patients; 95% CI 40.7%, 64.7%) vs 17.6% (13/74 patients; 95% CI 9.7%, 28.2%) with PBO+AZA (P < 0.0001). The CR rate by 24 weeks for IVO+AZA vs PBO+AZA was 37.5% and 10.8%, respectively. ORR with IVO+AZA was 62.5% (45/72 patients; 95% CI 50.3%, 73.6%) vs 18.9% (14/74 patients; 95% CI 10.7%, 29.7%) with PBO+AZA (P < 0.0001). All reported P-values are 1-sided. Common all-grade adverse events (AEs) occurring in > 20% of patients receiving IVO+AZA vs PBO+AZA were nausea (42.3% vs 38.4%), vomiting (40.8% vs 26.0%), diarrhea (35.2% vs 35.6%), pyrexia (33.8% vs 39.7%), anemia (31.0% vs 28.8%), febrile neutropenia (28.2% vs 34.2%), thrombocytopenia (28.2% vs 20.5%), constipation (26.8% vs 52.1%), and pneumonia (23.9% vs 31.5%). Sixty-six (93.0%) patients receiving IVO+AZA vs 69 (94.5%) patients receiving PBO+AZA experienced a grade ≥ 3 AE. Common grade ≥ 3 AEs occurring in > 20% of patients receiving IVO+AZA vs PBO+AZA included febrile neutropenia (28.2% vs 34.2%), anemia (25.4% vs 26.0%), thrombocytopenia (23.9% vs 20.5%), and pneumonia (22.5% vs 28.8%). Frequency of all-grade differentiation syndrome (DS) as assessed by investigators was 14.1% with IVO+AZA vs 8.2% with PBO+AZA, and that of grade ≥ 3 DS was 4.2% with IVO+AZA vs 4.1% with PBO+AZA. Based on the recommendation of the Independent Data Monitoring Committee, further enrollment into the study was prematurely discontinued due to evidence of benefit. Conclusions: IVO+AZA significantly improved EFS, OS, and clinical response (CR, CR+CRh, ORR) compared with PBO+AZA in patients with IC-ineligible, newly diagnosed m IDH1 AML. The safety profile of IVO+AZA was favorable and consistent with previous studies. These data demonstrate the clinical benefit of IVO+AZA in this difficult-to-treat AML population. Disclosures Montesinos: Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Stemline/Menarini: Consultancy; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Forma Therapeutics: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Glycomimetics: Consultancy; Tolero Pharmaceutical: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Recher: Incyte: Honoraria; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; MaatPharma: Research Funding; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Wang: AbbVie: Consultancy; Astellas Pharma, Inc.: Research Funding. Heuser: Tolremo: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer Pharma AG: Research Funding; Astellas: Research Funding; BergenBio: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Calado: AA&MDS International Foundation: Research Funding; Agios: Membership on an entity's Board of Directors or advisory committees; Team Telomere, Inc.: Membership on an entity's Board of Directors or advisory committees; Novartis Brasil: Honoraria; Instituto Butantan: Consultancy; Alexion Brasil: Consultancy. Schuh: Kite/Gilead: Research Funding; GlycoMimetics: Research Funding; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Membership on an entity's Board of Directors or advisory committees; Teva: Honoraria, Membership on an entity's Board of Directors or advisory committees. Daigle: Agios: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Servier: Current Employment. Hui: Servier: Current Employment; Agios: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Boehringer Ingelheim: Ended employment in the past 24 months. Zhang: Servier: Current Employment; Agios: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Pandya: Agios: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Servier: Current Employment. Gianolio: Servier: Current Employment; Agios: Current equity holder in publicly-traded company, Ended employment in the past 24 months. de Botton: Pierre Fabre: Other; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Syros: Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Forma Therapeutics: Honoraria, Research Funding; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees. Döhner: Oxford Biomedicals: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; GEMoaB: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Pfizer: Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Berlin-Chemie: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Jazz: Consultancy, Honoraria, Research Funding; Helsinn: Consultancy, Honoraria; Astex: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Ulm University Hospital: Current Employment. OffLabel Disclosure: 1) Ivosidenib (AG-120) is an isocitrate dehydrogenase-1 (IDH1) inhibitor indicated for the treatment of acute myeloid leukemia (AML) with a susceptible IDH1 mutation as detected by an FDA-approved test in: i) Adult patients with newly diagnosed AML who are 75 years of age or older or who have comorbidities that preclude use of intensive induction chemotherapy ii) Adult patients with relapsed or refractory AML. 2) It is being evaluated in a clinical trial in combination with azacitidine in adults 18 years of age or older with previously untreated acute myeloid leukemia with an IDH1 mutation.