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Recurrent somatic internal tandem duplications (ITD) in the FMS‐like tyrosine kinase 3 (FLT3) gene characterise approximately one third of patients with acute myeloid leukaemia (AML), and FLT3‐ITD mutation status guides risk‐adapted treatment strategies. The aim of this work was to characterise FLT3‐ITD variant distribution in relation to molecular and clinical features, and overall survival in adult AML patients. We performed two parallel retrospective cohort studies investigating FLT3‐ITD length and expression by cDNA fragment analysis, followed by Sanger sequencing in a subset of samples. In the two cohorts, a total of 139 and 172 mutant alleles were identified in 111 and 123 patients, respectively, with 22% and 28% of patients presenting with more than one mutated allele. Further, 15% and 32% of samples had a FLT3‐ITD total variant allele frequency (VAF), Internal tandem duplications (ITD) in the FMS‐like tyrosine kinase 3 (FLT3) gene is present in 20–30% of acute myeloid leukaemia (AML) patients. Here, we perform molecular profiling of FLT3‐ITD mutations in 263 AML patients. We provide a comprehensive overview of the heterogeneity and impact of FLT3‐ITD mutations by assessing various molecular features and the relationship with clinical features and overall survival.

Incidence, molecular presentation and outcome of acute myeloid leukaemia (AML) are influenced by sex, but little attention has been directed at untangling sex‐related molecular and phenotypic differences between female and male patients. While increased incidence and poor risk are generally associated with a male phenotype, the poor prognostic FLT3 internal tandem duplication (FLT3‐ITD) mutation and co‐mutations with NPM1 and DNMT3A are overrepresented in female AML. Here, we have investigated the relationship between sex and FLT3‐ITD mutation status by comparing clinical data, mutational profiles, gene expression and ex vivo drug sensitivity in four cohorts: Beat AML, LAML‐TCGA and two independent HOVON/SAKK cohorts, comprising 1755 AML patients in total. We found prevalent sex‐associated molecular differences. Co‐occurrence of FLT3‐ITD, NPM1 and DNMT3A mutations was overrepresented in females, while males with FLT3‐ITDs were characterized by additional mutations in RNA splicing and epigenetic modifier genes. We observed diverging expression of multiple leukaemia‐associated genes as well as discrepant ex vivo drug responses, suggestive of discrete functional properties. Importantly, significant prognostication was observed only in female FLT3‐ITD‐mutated AML. Thus, we suggest optimization of FLT3‐ITD mutation status as a clinical tool in a sex‐adjusted manner and hypothesize that prognostication, prediction and development of therapeutic strategies in AML could be improved by including sex‐specific considerations., Internal tandem duplications (ITDs) in the FMS‐like tyrosine kinase 3 (FLT3) gene are linked to poor prognosis in acute myeloid leukaemia (AML). Here, we investigated sex‐related differences in mutation, gene expression and drug sensitivity profiles in FLT3‐ITD‐mutated AML. We demonstrated significant sex‐associated molecular and functional differences, and surprisingly identified significant prognostication related to FLT3‐ITD only in female AML patients.

Little attention has been directed at untangling sex-related molecular and phenotypic differences in AML. While increased incidence and poor risk is generally associated with a male phenotype, FLT3-ITD, NPM1 and DNMT3A mutations are overrepresented in female AML. Here, we have investigated the relationship between sex and FLT3-ITD mutation status by comparing clinical data, mutational profiles, gene expression and ex vivo drug sensitivity responses in four cohorts: the Beat AML cohort, the LAML-TCGA cohort and two independent HOVON/SAKK clinical trial-associated cohorts, comprising a total of 1755 AML patients. We found that sex-associated molecular differences were prevalent in FLT3-ITD mutated AML. Co-occurrence of FLT3-ITD, NPM1 and DNMT3A mutations was overrepresented in females, while males with FLT3-ITDs were characterised by additional mutations in genes involved in RNA splicing and epigenetic modification. Female and male FLT3-ITD mutated AML had diverging expression of multiple leukemia-associated genes, as well as discrepant ex vivo drug-responses, suggestive of discrete functional properties. Surprisingly, we found significant prognostication of FLT3-ITD only in female patients. Thus, we suggest optimisation of FLT3-ITD mutation status as a clinical tool in a sex-adjusted manner. We further hypothesize that prognostication, prediction and development of therapeutic strategies in AML can be improved by including sex-specific considerations.

Acute myeloid leukemia (AML) is characterized by extensive clinical and biological heterogeneity. Despite vast advances in understanding the molecular pathology in AML during the last two decades few new AML therapeutics have been approved by the European Medicines Agency. Since 2005 only the epigenetic modulators decitabine and azacytidine, as well as histamine (plus interleukin- 2) have been approved against AML. None of these have outstanding efficiency, and decitabine and azacytdine have only been incorporated in frontline therapy of AML with limited enthusiasm. The majority of AML patients are frail and elderly, and lack of mild but effective agents for this patient cohort constitutes a major unmet need as overall survival remains poor. Along with the recent advancements in the molecular characterization of AML, numerous targeted therapies have been tested in clinical trials. In this review, we discuss the biological rationale for a selection of these novel therapeutic approaches, including epigenetic modifiers, agents targeting signalling pathways and inhibitors of nuclear-cytoplasmic shuttling. Further we discuss some of the possible shortcomings in current trial design that could explain the apparent incoherence between our improved biological knowledge and the lack of progress in therapy development of AML.

Internal tandem duplications (ITDs) of the gene encoding the Fms-Like Tyrosine kinase-3 (FLT3) receptor are present in approximately 25% of patients with acute myeloid leukemia (AML). The mutation is associated with poor prognosis, and the aberrant protein product has been hypothesized as an attractive therapeutic target. Various tyrosine kinase inhibitors (TKIs) have been developed targeting FLT3, but in spite of initial optimism the first generation TKIs tested in clinical studies generally induce only partial and transient hematological responses. The limited treatment efficacy generally observed may be explained by numerous factors; extensively pretreated and high risk cohorts, suboptimal pharmacodynamic and pharmacokinetic properties of the compounds, acquired TKI resistance, or the possible fact that inhibition of mutated FLT3 alone is not sufficient to avoid disease progression. The second-generation agent quizartinb is showing promising outcomes and seems better tolerated and with less toxic effects than traditional chemotherapeutic agents. Therefore, new generations of TKIs might be feasible for use in combination therapy or in a salvage setting in selected patients. Here, we sum up experiences so far, and we discuss the future outlook of targeting dysregulated FLT3 signaling in the treatment of AML.