A Trial of the FMS-like Tyrosine Kinase 3 (FLT3) Inhibitor Gilteritinib Administered as Maintenance Therapy Following Allogeneic Transplant for Patients With FLT3/Internal Tandem Duplication (ITD) Acute Myeloid Leukemia (AML)

Registration Inclusion Criteria

• Participant is considered a suitable candidate for HCT and has an acceptable source of allogeneic donor stem cells, as defined per institutional practice (allogeneic HCT for any donor source [matched sibling, unrelated donor (URD), mismatched URD, related haploidentical, or umbilical cord blood] and any graft source [umbilical cord, BM, peripheral blood (PB)], and any conditioning [myeloablative conditioning (MAC), reduced intensity conditioning (RIC), or non-myeloablative conditioning (NMA)] will be permitted).
• Participant is considered a legal adult by local regulation at the time of signing informed consent form (ICF).
• Participant consents to allow access to diagnostic BM aspirate or PB sample and/or the DNA derived from that sample, if available, that may be used to validate a companion diagnostic that is being developed in parallel with gilteritinib.
• Participant has confirmed, morphologically documented AML in CR1. For the purposes of registration, CR1 will be defined as 40 mL/min/1.73m2 as calculated with the Cockcroft-Gault equation with adjustment if total body weight is ≥ 125% of ideal body weight.
• Total bilirubin (TBL) ≤ 2.5 mg/dL, except for participants with Gilbert's syndrome.
• Serum AST and/or alanine aminotransferase (ALT) 40 mL/min/1.73m2 as calculated with the Cockcroft-Gault equation with adjustment if total body weight is ≥ 125% of ideal body weight.
• TBL 0.5 mg/kg of prednisone (or equivalent) daily dose within 1 week of randomization
• No escalation of systemic immunosuppression in terms of increase of corticosteroids or addition of new agent / modality within 2 weeks of randomization. (Note that increasing calcineurin inhibitors or sirolimus to achieve therapeutic trough levels is allowed.) Topical skin and topical gastrointestinal steroids are allowed.
• Participant is able to take oral medication.

Registration Exclusion Criteria

• Participant has had a prior allogeneic transplant.
• Participant has Karnofsky performance status score 450 msec (average of triplicate determinations) per central read.
• Participant has long QT Syndrome at screening.
• Participant has a known infection with human immunodeficiency virus (HIV).
• Participant has active hepatitis B infection as determined by NAAT or surface antigen assay. Participants who have acquired immunity from past exposure (HBcAb positive / HBsAb positive / HBsAg negative) are eligible.
• Participant has active hepatitis C infection as determined by NAAT. NAAT must be performed if the participant has positive serology for hepatitis C. Participants who have had past exposure and have no detectable virus either through spontaneous clearance or treatment are eligible.
• Participant has an uncontrolled infection. If a bacterial or viral infection is present, the participant must be receiving definitive therapy and have no signs of progressing infection for 72 hours prior to registration. If a fungal infection is present, the participant must be receiving definitive systemic anti-fungal therapy and have no signs of progressing infection for 1 week prior to registration.
• Progressing infection is defined as hemodynamic instability attributable to sepsis or new symptoms, worsening physical signs or radiographic findings attributable to infection.
• Persisting fever without other signs or symptoms will not be interpreted as progressing infection.
• Participant has had a myocardial infarction within 6 months prior to registration or New York Heart Association (NYHA) Class III or IV heart failure, uncontrolled angina, severe uncontrolled ventricular arrhythmias, or electrocardiographic evidence of acute ischemia.
• Participant has a serious medical or psychiatric illness likely to interfere with participation in this clinical study.
• Participant is breast feeding or pregnant.
• Participant has prior malignancies, except lobular breast carcinoma in situ, fully resected basal cell or squamous cell carcinoma of skin o