Medium-sized FLT3 internal tandem duplications confer worse prognosis than short and long duplications in a non-elderly acute myeloid leukemia cohort

Internal tandem duplications (ITDs) of the fms-like tyrosine kinase 3 (FLT3) gene occur in about 25% of patients with adult acute myeloid leukemia (AML). The aim of our study was to investigate the frequency of FLT3-ITD mutations followed by a detailed analysis of the mutational load and size of ITD insertions in a cohort consisting of 324 patients younger than 60 years old and treated with curative intention. FLT3-ITD alone did not influence overall survival (OS) or disease-free survival (DFS). We observed worse OS and DFS for patients with high mutational load indicative for loss of the FLT3 wild type allele (p = 0.010, p = 0.038, respectively). In multivariate analyses, patients with FLT3-ITD48-60bp showed worse OS and DFS compared to other groups (FLT3-ITDneg, FLT3-ITD<48b, FLT3-ITD>60bp; p = 0.014, p = 0.019, respectively). Our novel observation suggested that not only high FLT3-ITD load, but also medium-sized ITD insertions (48-60 bp) represented an adverse prognostic subgroup of patients with AML.