Deep Sequencing of <i>FLT3</i> ‐ITD Enables Response Evaluation and Post‐Treatment Monitoring in Childhood AML: An Exploratory Study

ABSTRACT Background An internal tandem duplication in the gene encoding Fms‐like tyrosine kinase 3 ( FLT3 ‐ITD) is associated with high relapse risk and poor prognosis in acute myeloid leukemia (AML) and plays a crucial role in treatment decisions. Measurable residual disease (MRD) analysis of FLT3 ‐ITD during and after treatment has shown prognostic value in adults, but its clinical value in children remains unexplored. Procedure This study evaluated the potential of MRD analysis with deep sequencing (ultrahigh‐sensitivity next‐generation sequencing; UHS‐NGS) of FLT3 ‐ITD to assess treatment response and predict impending relapse in children with AML. A total of 168 samples from 17 patients (median age 11 years, range: 4–17) were analyzed. Bone marrow samples were used for evaluation of treatment response, and peripheral blood samples for post‐treatment monitoring. Results Deep sequencing enabled monitoring of the kinetics of FLT3 ‐ITD subclones throughout treatment. When used for post‐treatment monitoring, deep sequencing detected increasing levels of FLT3 ‐ITD in peripheral blood only in patients who relapsed, while no such increase was detected in patients in continuous complete remission. Comparisons with flow cytometry and deep sequencing of other mutations confirmed the sensitivity of the assay and the often subclonal nature of FLT3 ‐ITD. Conclusions Deep sequencing of FLT3 ‐ITD is a highly sensitive method for MRD monitoring in children with AML, with significant potential for assessing treatment response and detecting imminent relapse at an early stage. It may serve as a valuable molecular MRD method, especially as a complement to flow cytometry.