Gilteritinib, a novel, highly specific, potent fms-like tyrosine kinase 3/AXL 
inhibitor, demonstrated antileukemic activity in patients with 
relapsed/refractory (R/R) acute myeloid leukemia (AML). In this open-label phase 
1 study (NCT02181660), Japanese patients (aged ≥18 years) with R/R AML received 
once-daily gilteritinib, escalating from 20 to 300 mg/d. Primary endpoints were 
safety/tolerability, including the maximum tolerated dose (MTD) and the 
recommended dose (RD); secondary endpoints were antileukemic activity and 
pharmacokinetics (PK). Twenty-four Japanese patients with R/R AML received 
once-daily oral gilteritinib in 1 of 6 dose-escalation cohorts (20, 40, 80, 120, 
200, and 300 mg/d). Gilteritinib was well tolerated. The MTD was 200 mg/d; 
dose-limiting toxicities were grade 3 tumor lysis syndrome (120 mg/d; n = 1); 
and grade 3 elevated blood lactate dehydrogenase, amylase, blood creatine 
phosphokinase levels, and syncope (all n = 2; 300 mg/d). The RD was 120 mg/d. 
The most common drug-related grade ≥3 adverse events were thrombocytopenia 
(n = 4 [16.7%]) and increased blood creatine phosphokinase (n = 3 [12.5%]). 
Gilteritinib had a dose-proportional PK profile. Among patients with mutated 
fms-like tyrosine kinase 3, the overall response rate (ORR) was 80% (n = 4 of 5; 
complete remission [CR] with incomplete platelet recovery, 1 [20%]; CR with 
incomplete hematologic recovery, 2 [40%]; partial remission (PR), 1 [20%]). 
Among patients with wild-type fms-like tyrosine kinase 3, ORR was 36.4%; (n = 4 
of 11; CR, 1 [9.1%]; CR with incomplete platelet recovery, 2 [18.2%]; PR, 1 
[9.1%]). In conclusion, gilteritinib was well tolerated and demonstrated 
antileukemic activity in a Japanese R/R AML population.