FMS-like tyrosine kinase 3 (FLT3) mutations represent some of the most pivotal genetic alterations in acute myeloid leukemia (AML), influencing disease biology, risk stratification, and treatment response. This review highlights the structural, functional, and clinical aspects of FLT3 mutations, emphasizing the transformative role of next-generation sequencing (NGS) in mutation detection, measurable residual disease (MRD) monitoring, and precision therapy.
Introduction
FLT3 encodes a receptor tyrosine kinase that regulates hematopoietic progenitor cell proliferation and differentiation. Mutations—especially internal tandem duplications (ITD) and tyrosine kinase domain (TKD) point mutations—result in constitutive signaling and leukemogenesis. These mutations are most prevalent in AML (~30%) and less commonly in myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML), acute lymphoblastic leukemia (ALL), and mixed phenotype acute leukemia (MPAL). Early detection of FLT3 mutations is crucial, as they significantly impact prognosis and guide targeted therapy.
FLT3 Gene and Protein Structure
The FLT3 gene on chromosome 13q12 comprises 24 exons encoding the extracellular, transmembrane, juxtamembrane (JMD), and tyrosine kinase domains (TKD). Structurally, the receptor is tightly regulated, with JMD serving as an autoinhibitory region. Ligand binding triggers dimerization and phosphorylation, activating downstream pathways such as PI3K/AKT, MAPK/ERK, and STAT, which drive hematopoiesis and immune cell development.
FLT3 Mutations and Clinical Relevance
FLT3 mutations include:
FLT3-ITD mutations correlate with aggressive disease and poor survival, while TKD mutations have more variable outcomes, influenced by co-occurring mutations like NPM1 or CEBPA. Some rare variants (e.g., V592A, N676K) confer sensitivity or resistance to FLT3 inhibitors.
Spectrum Across Hematologic Malignancies
FLT3 mutations are most common in AML but also appear in:
Their variable frequency and prognostic impact across diseases underscore the need for precise molecular profiling.
FLT3 as a Therapeutic Target
FLT3 inhibitors are classified into:
FDA-approved agents include:
Resistance mechanisms (e.g., secondary TKD mutations, activation of bypass pathways) prompt exploration of combination therapies with BCL-2, MEK, or hypomethylating agents.
FLT3 Mutation Detection in Clinical Labs
Historically, detection relied on PCR with fragment length analysis (PCR-FLA), which is rapid but limited in sensitivity and mutation detail. NGS now offers:
Challenges in detecting long ITDs and insertions/deletions are being addressed through advanced bioinformatics (e.g., FLT3_ITD_ext, ITDseek) and optimized hybrid capture or amplicon-based methods.
MRD Detection and Monitoring
FLT3-ITD MRD, once thought unreliable, is now a powerful predictor of relapse and survival. NGS-based MRD testing allows detection of residual leukemic clones at very low levels (0.01% or lower). Studies show:
Standardization of MRD testing protocols, input material, and informatics is urgently needed for broader clinical implementation.
Conclusion
FLT3 mutations represent a cornerstone in the pathogenesis and treatment of AML. The integration of NGS into clinical workflows enhances mutation detection, risk stratification, and MRD monitoring. FLT3 inhibitors—particularly in combination regimens—offer promising avenues for durable remission. Continued research into molecular heterogeneity and standardized MRD protocols will refine personalized therapies and improve outcomes in FLT3-mutated hematologic malignancies.
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Journal of Clinical and Translational Pathology
Molecular Testing of FLT3 Mutations in Hematolymphoid Malignancies in the Era of Next-generation Sequencing
30-Mar-2025