A call for revision of the World Health Organization classification system to include FLT3-ITD as a distinct entity

Abstract

Acute Myeloid Leukemia (AML) is a heterogeneous malignancy driven by over 200 different cytogenetic abnormalities, giving rise to eight different subtypes, each identified as having a unique prognostic outcome and response to treatment. The World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia describes specific subtypes and is widely used to treat and diagnose AML. However, the current WHO classification system is based primarily on treatment outcomes for adult patients. In recent years, the incorporation of genetic and molecular testing has aided in the identification of several distinct subtypes that are not yet recognized by the WHO classification system. One key genomic driver in some cases of AML is the internal tandem duplication (ITD) within the gene that codes for the FMS-like tyrosine kinase receptor-3 (FLT3). Pediatric AML patients with FLT3-ITD consistently have high relapse rates and low overall survival rates, which may be improved by intensifying and specifying treatment regimens. Despite increasing research showing the prognostic significance of FLT3-ITD AML and development of FLT3 inhibitors, this cytogenetically unique form of AML with a distinctly poor prognosis in children is not mentioned in the current WHO classification. The authors suggest the need for inclusion of FLT3-ITD as a distinct entity in the WHO classification due to its prognostic effect in pediatric AML in particular. Though advancements have been made in the understanding and treatment of FLT3-ITD AML, the application of current and future research will be limited without the inclusion of FLT3-ITD as a distinct entity.