The purpose of this study is to determine the clinical benefit of ASP2215 therapy in participants with FMS-like tyrosine kinase (FLT3) mutated AML who are refractory to or have relapsed after first-line AML therapy as shown with overall survival (OS) compared to salvage chemotherapy. In addition, this study will evaluate safety as well as determine the overall efficacy in event-free survival (EFS) and complete remission (CR) rate of ASP2215 compared to salvage chemotherapy.