Mutation spectrum of FLT3 and significance of non‐canonical FLT3 mutations in haematological malignancy

Abstract

Summary Fms‐like tyrosine kinase 3 (FLT3) is frequently mutated in haematological malignancies. Although canonical FLT3 mutations including internal tandem duplications (ITDs) and tyrosine kinase domains (TKDs) have been extensively studied, little is known about the clinical significance of non‐canonical FLT3 mutations. Here, we first profiled the spectrum of FLT3 mutations in 869 consecutively newly diagnosed acute myeloid leukaemia (AML), myelodysplastic syndrome and acute lymphoblastic leukaemia patients. Our results showed four types of non‐canonical FLT3 mutations depending on the affected protein structure: namely non‐canonical point mutations (NCPMs) (19.2%), deletion (0.7%), frameshift (0.8%) and ITD outside the juxtamembrane domain (JMD) and TKD1 regions (0.5%). Furthermore, we found that the survival of patients with high‐frequency (>1%) FLT3‐NCPM in AML was comparable to those with canonical TKD. In vitro studies using seven representative FLT3‐deletion or frameshift mutant constructs showed that the deletion mutants of TKD1 and the FLT3‐ITD mutant of TKD2 had significantly higher kinase activity than wild‐type FLT3, whereas the deletion mutants of JMD had phosphorylation levels comparable with wild‐type FLT3. All tested deletion mutations and ITD were sensitive to AC220 and sorafenib. Collectively, these data enrich our understanding of FLT3 non‐canonical mutations in haematological malignancies. Our results may also facilitate prognostic stratification and targeted therapy of AML with FLT3 non‐canonical mutations.

FLT3-TKD Measurable Residual Disease Detection Using Droplet Digital PCR and Clinical Applications in Acute Myeloid Leukemia

“…Furthermore, targeted ddPCR assays for variants at non-canonical FLT3 -TKD sites may not be available commercially. NGS methods mentioned previously may be required to monitor these variants sensitively (if deemed pathogenic) [ 20 ]. A second limitation of the assay is that there is a cross-reactivity of assays with related mutations (e.g., the D835Y assay detects D835V/H/E/I836del variants).…”