Prognostic Weight of FLT3-ITD Allelic Ratio in Newly Diagnosed Acute Myeloid Leukemia

Abstract

Background: FLT3 internal tandem duplication (ITD) is among the most common and prognostically consequential mutations in newly diagnosed acute myeloid leukemia (AML), but its clinical impact is not uniform across patients.

Objective: To synthesize the published evidence on how the FLT3-ITD mutant-to-wild-type allelic ratio, rather than mutation presence alone, shapes prognosis, interacts with NPM1 co-mutation status, and informs the use of FLT3 inhibitors and allogeneic transplantation.

Methods: Narrative review of landmark cohort studies, European LeukemiaNet risk-classification updates, and randomized phase 3 trials of midostaurin, gilteritinib, quizartinib, and sorafenib in FLT3-mutated AML.

Findings: High allelic ratio (>=0.5) confers markedly worse relapse-free and overall survival than low-ratio disease, an effect layered onto NPM1 mutation status; FLT3 inhibitors improve survival across the newly diagnosed and relapsed/refractory settings, and inhibitor-era trials have generally not shown ratio to modify drug benefit, prompting the 2022 ELN revision that removed the ratio-based split for NPM1-mutated, FLT3-ITD-positive disease.

Conclusions: Allelic ratio remains a useful marker of FLT3 dependency and relapse risk that should inform transplant referral and maintenance decisions, but its role is increasingly one input among measurable residual disease and co-mutation data rather than a standalone risk cutoff.