AML Classifications: WHO vs ICC 2022 Update

Besides WHO's classification, ICC's system for AML diagnosis and treatment is also available since 2022. How do they differ and which should be followed?

The following is a summary of the article “Definitions of Acute Myeloid Leukaemia and their clinical significance according to the WHO 2022 and ICC classification” by Donata Backhaus et al (University of Leipzig Medical Center, Germany), which is part of the Proceedings of the 4th European Congress controversies in Leukemias, held in Brussels, Belgium, 20-21 November, 2023

Acute myeloid leukaemia (AML) classification has long been the cornerstone of diagnosing and treating this challenging hematologic malignancy. Over the years, the World Health Organisation (WHO) classification has provided a comprehensive framework integrating clinical, morphological, immunophenotypic, and genetic features. However, with advancements in our understanding of AML biology, revisions to the classification have been necessary every 5 to 10 years.

The collaboration between the WHO, leading haematopathologists, oncologists, haematologists, and geneticists has historically driven these updates, ensuring widespread acceptance and utilisation. However, the release of the fifth edition in 2022 marked a divergence from this tradition, opting for informed bibliometrics over the Clinical Advisory Committee (CAC) model. This shift sparked debates, leading to the organisation of a separate CAC in 2020, whose findings culminated in the creation of the International Consensus Classification of Myeloid and Lymphoid Neoplasms (ICC).

Consequently, we now find ourselves in a landscape with two competing classification systems for AML, each with its nuances and implications for patient care. In our comprehensive analysis, we delve into the similarities and differences between the WHO 2022 and ICC classifications, shedding light on their impact on accurate patient diagnoses and risk stratification.

One of the key areas of contention lies in defining the boundary between myelodysplastic syndromes (MDS) and AML. While both classifications retained the 20% blast threshold for AML diagnosis, the introduction of the MDS/AML category by the ICC highlights the biological continuum between these diseases and the need for tailored therapeutic approaches.

Furthermore, the inclusion of AML-defining genetic abnormalities underwent significant expansions, reflecting our evolving knowledge of AML genetics. However, discrepancies in defining genetic subgroups and blast thresholds underscore the complexities of disease classification.

Real-world assessments of the WHO 2022 and ICC classifications reveal shifts in patient allocation and prognostic implications. Despite a high degree of congruence, discrepancies in defining genetic subgroups and AML-MR highlight areas of ongoing debate and potential refinement.

Moreover, the implications of these classifications extend to risk stratification systems such as the European LeukemiaNet (ELN) 2022, where adjustments reflect the evolving landscape of AML biology and prognosis.

In conclusion, while both the WHO 2022 and ICC classifications represent significant advancements in AML classification, their coexistence presents challenges in clinical practice and research. Moving forward, efforts to reconcile discrepancies and foster a unified classification system are essential to advance patient care and streamline international collaboration in AML research and treatment.

For the full text article published by Medicom Medical Publishers, see Backhaus et al. Proceedings of the 4th European Congress Controversies in Leukemia,  Brussels, Belgium, 20-21 November, 2023.