FLT3-ITD (internal tandem duplication)

aka FLT3-ITD, FLT3 ITD, FLT3 internal tandem duplication, FLT3-ITD positive, FLT3-ITD allelic ratio, ITD-positive AML

FLT3-ITD is a duplicated stretch of the FLT3 receptor gene found in about a quarter of acute myeloid leukaemias; it makes relapse more likely and is treated with midostaurin, quizartinib or gilteritinib.

Internal tandem duplications in the juxtamembrane domain are detected by PCR fragment analysis (the LeukoStrat CDx FLT3 Mutation Assay reports ITD and the TKD mutations D835 and I836) or by sequencing; the allelic ratio once used in ELN risk stratification was dropped in ELN 2022. Midostaurin (Rydapt) is labelled for newly diagnosed FLT3 mutation-positive AML with induction and consolidation chemotherapy; quizartinib (Vanflyta, 2023) specifically for FLT3-ITD-positive newly diagnosed AML including maintenance; gilteritinib (Xospata) for relapsed or refractory AML with a FLT3 mutation. All three name an FDA-approved test, and the LeukoStrat assay is the companion diagnostic for each.

Part ofFLT3· FLT3Other readoutsFLT3-TKD All readouts

FLT3: what it is and how drugs act on it · animated schematic, not to scale

Target · the protein and the cell it sits on
Drug · antibody, small molecule, cell or radioligand
Effect · signal, damage or kill

In plain words · FLT3 is a kinase mutated in about a third of acute myeloid leukaemias, where adding an inhibitor to chemotherapy improves survival.

Sequencing 3 approval thresholds

What it means for a patient

A FLT3-ITD result at diagnosis means a FLT3 inhibitor (midostaurin or quizartinib) is added to chemotherapy from the first cycle, and it strengthens the case for a stem cell transplant in first remission. If the leukaemia comes back, gilteritinib tablets are on label. The test must be back within days, so ask that it be sent at diagnosis.

Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.

Scoring rule

An internal tandem duplication in FLT3 exons 14 to 15 detected by PCR fragment analysis (LeukoStrat CDx) or sequencing of blood or marrow; the assay's positivity uses a signal ratio cut-off of 0.05.

“ITD mutations and TKD mutations D835 and I836”
FDA: List of FDA-Authorized Companion Diagnostic Devices

Thresholds used in approvals

Threshold	Drug	Cancer	Regulator	Source
FLT3-ITD-positive	Quizartinib	FLT3-mutated acute myeloid leukaemia	FDA	label
FLT3 mutation-positive (ITD or TKD)	Midostaurin	FLT3-mutated acute myeloid leukaemia	FDA	label
FLT3 mutation (ITD or TKD), relapsed or refractory	Gilteritinib	FLT3-mutated acute myeloid leukaemia	FDA	label

Drugs whose label names it

Quizartinib Midostaurin Gilteritinib

Companion diagnostics (FDA list)

Device	Maker	Indication and sample	Drug	PMA / 510(k)
LeukoStrat CDx FLT3 Mutation Assay	Invivoscribe Technologies	Acute Myelogenous Leukemia - Peripheral Blood or Bone Marrow	Midostaurin	P160040 (04/28/2017)
LeukoStrat CDx FLT3 Mutation Assay	Invivoscribe Technologies	Acute Myelogenous Leukemia - Peripheral Blood or Bone Marrow	Gilteritinib	P160040/S002 (11/28/2018)
LeukoStrat CDx FLT3 Mutation Assay	Invivoscribe Technologies	Acute Myeloid Leukemia (AML) - Peripheral Blood or Bone Marrow	Quizartinib	P160040/S011 (07/20/2023)

Tests that measure it

LeukoStrat CDx FLT3 Mutation Assay FoundationOne Heme NeoGenomics NeoTYPE profiles

Trials that name this readout

Matched on the name and aliases of the readout in the title, setting and summary of each trial; a match is a mention, not proof the readout was an entry criterion.