BACKGROUND: Patients with relapsed or refractory (R/R) acute myeloid leukemia (AML) and confirmed feline McDonough sarcoma (FMS)-like tyrosine kinase 3 gene mutations ( FLT3 mut+ ) have a poor prognosis and limited effective treatment options. Gilteritinib is the first targeted therapy approved in the United States and Europe for R/R FLT3 mut+ AML with significantly improved efficacy compared with existing treatments. OBJECTIVE: To evaluate gilteritinib against salvage chemotherapy (SC) and best supportive care (BSC) over a lifetime horizon among adult patients with R/R FLT3 mut+ AML from a US third-party payer's perspective. METHODS: The model structure of this cost-effectiveness analysis included a decision tree to stratify patients based on their hematopoietic stem cell transplantation (HSCT) status, followed by 2 separate 3-state partitioned survival models to predict the long-term health status conditional on HSCT status. The ADMIRAL trial data and literature were used to predict probabilities of patients being in different health states until a conservative cure point at year 3. Afterwards, living patients followed the survival outcomes of long-term survivors with AML. Model inputs for utilities, medical resource use, and costs were based on the ADMIRAL trial, published literature, and public sources. All costs were inflated to 2019 US dollars (USD). Total incremental costs (in 2019 USD), life-years (LYs), quality-adjusted LYs (QALYs), and incremental cost-effectiveness ratios (ICERs) were calculated. Deterministic sensitivity analyses and probabilistic sensitivity analyses were performed. RESULTS: This work was supported by Astellas Pharma, Inc., which was involved in all stages of the research and manuscript development. Garnham, Pandya, and Shah are employees of Astellas and hold stock/stock options. Zeidan consulted and received personal fees/honoraria and research funding from Astellas. Zeidan also has received research funding from Celgene/BMS, Abbvie, Astex, Pfizer, Medimmune/AstraZeneca, Boehringer-Ingelheim, Trovagene/Cardiff Oncology, Incyte, Takeda, Novartis, Amgen, Aprea, and ADC Therapeutics; has participated in advisory boards; has consulted with and/or received honoraria from AbbVie, Otsuka, Pfizer, Celgene/BMS, Jazz, Incyte, Agios, Boehringer-Ingelheim, Novartis, Acceleron, Daiichi Sankyo, Taiho, Seattle Genetics, BeyondSpring, Cardiff Oncology, Takeda, Ionis, Amgen, Janssen, Syndax, Gilead, Kura, Aprea, Lox Oncology, Genentech, Servier, Jasper, Tyme, and Epizyme; has served on clinical trial committees for Novartis, Abbvie, Geron, Gilead, Kura, Lox Oncology, BioCryst, and Celgene/BMS; and has received travel support for meetings from Pfizer, Novartis, and Cardiff Oncology. Qi and Yang are employees of Analysis Group, Inc., which received consulting fees from Astellas for work on this study. Part of this material was presented at the American Society of Hematology (ASH) Annual Meeting; December 7-10, 2019; Orlando, FL.CONCLUSIONS: Gilteritinib is a cost-effective novel treatment for patients with R/R FLT3 mut+ AML in the United States. DISCLOSURES: This work was supported by Astellas Pharma, Inc., which was involved in all stages of the research and manuscript development. Garnham, Pandya, and Shah are employees of Astellas and hold stock/stock options. Zeidan consulted and received personal fees/honoraria and research funding from Astellas. Zeidan also has received research funding from Celgene/BMS, Abbvie, Astex, Pfizer, Medimmune/AstraZeneca, Boehringer-Ingelheim, Trovagene/Cardiff Oncology, Incyte, Takeda, Novartis, Amgen, Aprea, and ADC Therapeutics; has participated in advisory boards; has consulted with and/or received honoraria from AbbVie, Otsuka, Pfizer, Celgene/BMS, Jazz, Incyte, Agios, Boehringer-Ingelheim, Novartis, Acceleron, Daiichi Sankyo, Taiho, Seattle Genetics, BeyondSpring, Cardiff Oncology, Takeda, Ionis, Amgen, Janssen, Syndax, Gilead, Kura, Aprea, Lox Oncology, Genentech, Servier, Jasper, Tyme, and Epizyme; has served on clinical trial committees for Novartis, Abbvie, Geron, Gilead, Kura, Lox Oncology, BioCryst, and Celgene/BMS; and has received travel support for meetings from Pfizer, Novartis, and Cardiff Oncology. Qi and Yang are employees of Analysis Group, Inc., which received consulting fees from Astellas for work on this study. Part of this material was presented at the American Society of Hematology (ASH) Annual Meeting; December 7-10, 2019; Orlando, FL.