[Current status and challenges of AML treatment with FLT3 inhibitors]

FLT3 mutation is one of the most frequent genetic mutations in AML, identified in approximately 30% of patients, and FLT3-ITD mutation is considered a poor prognostic factor. Based on these molecular and clinical backgrounds, FLT3 mutations are considered promising therapeutic targets in AML, and intensive development of targeted therapeutics has been ongoing for more than two decades. Recently, combination of FLT3 inhibitors with intensive chemotherapy for untreated AML patients with FLT3 mutations and FLT3 inhibitor monotherapy for relapsed/refractory patients have been approved. In Japan, the combination of quizartinib and intensive chemotherapy for untreated FLT3-ITD-positive AML was approved in 2023. Clinical use of FLT3 inhibitors shows strong promise for improving the clinical outcomes of these AML patients with an extremely poor prognosis. Meanwhile, various resistance mechanisms to FLT3 inhibitors have been identified, including the emergence of resistance-associated mutations, and attenuated inhibitory effects of FLT3 inhibitors involving the bone marrow microenvironment surrounding AML cells. Thus, future efforts should aim to optimize combination therapy based on the characteristics of each FLT3 inhibitor, develop biomarkers that could inform treatment selection, and to better understand these resistance mechanisms and develop methods for overcoming them.