A practical approach on the classifications of myeloid neoplasms and acute leukemia: WHO and ICC

Abstract

In 2022, two new classifications of myeloid neoplasms and acute leukemias were published: the 5th edition WHO Classification (WHO-HAEM5) and the International Consensus Classification (ICC). As with prior classifications, the WHO-HAEM5 and ICC made updates to the prior classification (revised 4th edition WHO Classification, WHO-HAEM4R) based on a consensus of groups of experts, who examined new evidence. Both WHO-HAEM5 and ICC introduced several new disease entities that are based predominantly on genetic features, superseding prior morphologic definitions. While it is encouraging that two groups independently came to similar conclusions in updating the classification of myeloid neoplasms and acute leukemias, there are several divergences in how WHO-HAEM5 and ICC define specific entities as well as differences in nomenclature of certain diseases. In this review, we highlight the similarities and differences between the WHO-HAEM5 and ICC handling of myeloid neoplasms and acute leukemias and present a practical approach to diagnosing and classifying these diseases in this current era of two divergent classification guidelines.

Fig. 1

Precursor lesions and their evolution to myeloid neoplasm. Other clonal proliferations with cytopenia such as VEXAS syndrome, PNH and aplastic anemia are not shown here. CH, clonal hematopoiesis. CHIP, clonal hematopoiesis of indeterminate potential. CCUS, clonal cytopenia of undetermined significance. MDS, myelodysplastic neoplasms/syndromes. MPN, myeloproliferative neoplasms. AML, acute myeloid leukemia

Fig. 2

Algorithmic updates of AML classification. AML-RGA, AML with recurrent genetic abnormalities. AML-MRC, AML with myelodysplasia-related changes. AML-MR, AML, myelodysplasia-related. MR CGA, myelodysplasia related cytogenetic abnormalities. NOS, not otherwise specified