Abstract 2299: Development of a novel next-generation sequencing (NGS)-based assay for measurable residual disease (MRD) in FLT3-ITD acute myeloid leukemia (AML) and its potential clinical application in patients
Authors: Shi Wenge , Laing Christian , Ding Wei , Mycoco Marc , Lameh Jelveh , Pollner Reinhold 
Published: August 2019

Introduction The presence of MRD in patients with AML who are in morphologic remission has been shown to be a powerful predictor of eventual relapse. FMS-like tyrosine kinase 3 (FLT3) internal tandem duplications (ITD) confer a negative prognostic impact by increasing risk of relapse. The ability to detect FLT3-ITD mutations in remission bone marrow specimens is hampered by the limited sensitivity at 1% of PCR-based assays. To address such limitations, we developed a novel NGS-based MRD assay for the detection of FLT3-ITD mutations.

Method Genomic DNA was isolated from bone marrow (BM) aspirates or peripheral blood (PB) samples. PCR was performed to amplify exons 13 to 15 of the FLT3 gene. Highly diverse NGS libraries were then generated and sequenced using Illumina’s sequencer. Using a custom bioinformatics approach, unique FLT3-ITD mutations of varying lengths were identified and mutant allelic frequency calculated. The assay was validated using clinical samples and contrived samples. For accuracy assessment, 30 samples (including PB or BM remnant patient DNA and cell line DNA, above DNA diluted in normal DNA) were included. Data were compared with a Fragment Size Analysis by Capillary Electrophoresis assay. To assess precision, the assay was validated at multiple levels evaluating intra-assay, inter-assay, inter-operator, inter-instrument and inter-reagent lot precision. DNA samples from selected mutant cell lines representing different FLT3-ITD lengths were spiked into normal DNA to evaluate assay sensitivity and linearity.

Summary The ideal DNA input range was established as 300 ng to 500 ng. In all FLT3-ITD-positive cell line samples covering diverse FLT3-ITD lengths (6 bp to 156 bp), the FLT3-ITD MRD NGS assay showed 100% concordance with the reference assay. The assay is also capable of detecting ITDs as expected after the samples were diluted in normal DNA to mimic samples from patients in remission. All acceptance criteria for the different precision parameters were met. The lower limit of detection of 0.013% regardless of ITD length was established but the assay was capable of detecting FLT3-ITD mutations at a level as low as 0.003% without false-positive results. The assay was linear (R2 = 0.958) down to FLT3-ITD allele frequency levels of 0.035% or the lower limit of quantitation.

Conclusion Analytical validation results established the role of this NGS-based MRD assay for the clinical management of FLT3-ITD AML. The FLT3-ITD MRD NGS assay demonstrated high sensitivity and high specificity by detecting the unique length of each patient’s mutation with no false-positive results in expected negative samples. This assay might be helpful in defining the depth of remission, identifying persistent disease, and helping to guide decision making in the use of FLT3 inhibitors as continuation therapy.

Citation Format: Wenge Shi, Christian Laing, Wei Ding, Marc Mycoco, Jelveh Lameh, Reinhold Pollner. Development of a novel next-generation sequencing (NGS)-based assay for measurable residual disease (MRD) in FLT3-ITD acute myeloid leukemia (AML) and its potential clinical application in patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2299.