New classification of acute myeloid leukemia and precursor-related neoplasms: changes and unsolved issues

The World Health Organization (WHO) classification of lympho-hematopoietic neoplasms is increasingly based on genetic criteria. Here, we focus on changes that, as compared to the 2001 edition, were introduced into the 2008 WHO classification of acute myeloid leukemia (AML) and related precursor neoplasms. The category of AML with recurrent genetic abnormalities was expanded to account for 60% of AML by adding three distinct entities, i.e., AML with t(6,9), inv(3), or t(1;22), and two provisional entities, i.e., AML with mutated NPM1 or CEBPA. These changes have greatly modified the approaches to diagnosis and prognostic stratification of AML patients. To emphasize the need of various parameters for diagnosis, including myelodysplasia (MD)-related cytogenetic abnormalities, history of myelodysplasia or myelodysplasia/myeloproliferative neoplasm, and multilineage dysplasia, the category of "AML with multilineage dysplasia" was re-named AML with MD-related changes. Finally, we describe the unique characteristics of myeloid proliferations associated with Down syndrome and blastic plasmacytoid dendritic cell neoplasm.