WHO, what, when, where, and why: New classification systems for acute myeloid leukemia and their impact on clinical practice

Acute Myeloid Leukemia in Older Patients: From New Biological Insights to Targeted Therapies

Acute myeloid leukemia (AML) is a heterogeneous blood-related neoplasm that predominantly afflicts older adults with a poor prognosis due to their physical condition and the presence of medical accompanying comorbidities, adverse biological disease features, and suitability for induction intensive chemotherapy and allogenic stem cells transplantation. Recent research into the molecular and biological factors contributing to disease development and progression has led to significant advancements in treatment approaches for older patients with AML. This review article discusses the latest biological and therapeutic developments that are transforming the management of AML in older adults.

What is new in acute myeloid leukemia classification?

Recently, the International Consensus Classification (ICC) and the 5th edition of the World Health Organization classification (WHO2022) introduced diagnostically similar yet distinct approaches, which has resulted in practical confusion. This review compares these classification systems for acute myeloid leukemia (AML), building up on the revised 4th edition of WHO (WHO2016). Both classifications retain recurrent genetic abnormalities as a primary consideration. However, they differ in terms of blast threshold. The ICC mandates a minimum of 10% blasts in the bone marrow or peripheral blood, whereas the WHO2022 does not specify a blast cut-off. AML with BCR::ABL1 requires > 20% blast count in both classifications. In WHO2022, AML with CEBPA mutation requires > 20% blasts. TP53 mutation, a new entity is exclusive to ICC, diagnosed with > 20% blasts and variant allele frequency > 10%. AML with myelodysplasia-related changes is defined by cytogenetic or gene mutation-based criteria, not morphological dysplasia. Eight genes were common to both groups: ASXL1, BCOR, EZH2, SF3B1, SRSF2, STAG2, U2AF1, and ZRSR2. An additional gene, RUNX1, was included in the ICC classification. AML cases defined by differentiation (WHO2022) and AML not otherwise specified (ICC) are categorized as lacking specific defining genetic abnormalities, WHO2022 labels this as a myeloid neoplasm post cytotoxic therapy (MN-pCT), described as an appendix after specific diagnosis. Similarly, in ICC, it can be described as "therapy-related", without a separate AML category.