The purpose of this study is to compare relapse-free survival (RFS) between subjects with FMS-like tyrosine kinase 3 (FLT3) / internal tandem duplication (ITD) acute myeloid leukemia (AML) in first complete remission (CR1) and who are randomized to receive gilteritinib or placebo beginning after completion of induction/consolidation chemotherapy for a two-year period.