Revised World Health Organization Criteria-Defined Acute Myeloid Leukemia in a Large Cohort: Highlighting the Frequency and Characterization of Recategorized Cases

Abstract

Background: Application of the 2016 revised WHO criteria for categorization of acute myeloid leukemia (AML) highlights certain discrepancies from that of the 2008 WHO criteria. We thus analyzed the frequency, categorization patterns, and features of discrepant cases, and characterized the AML subtypes that had undergone major changes under the revised criteria. Methods: We divided the patients into the following seven categories based on the previous and the revised WHO criteria: AML with recurrent genetic abnormalities (RGA), AML with myelodysplasia-related changes (MRC), therapy-related AML, AML not otherwise specified (NOS), AML associated with Down syndrome, AML with subcategory not determined, and myelodysplastic syndrome (MDS). Results: In total, 1,185 AML cases were reviewed. The concordance rate in categorization between the two criteria was 93.4%. Among 78 discrepant cases, the three most common discrepancy patterns were for the RGA to NOS, MRC to MDS, and MRC to RGA, representing cases with a single mutation in CEBPA, erythroleukemia, and recurrent genetic abnormalities showing myelodysplasia, respectively. We identified three cases of erythroleukemia harboring an NPM1 mutation, who might clinically benefit from chemotherapy rather than MDS-oriented treatment; we also found AML with del(9q) in 3% of patients, which might contribute to leukemogenesis either via haploinsufficiency of deleted genes or gene-togene interaction. Conclusions: This study revealed that approximately 7% of patients with AML were reclassified into a different category due to the introduction of new entities, changed definitions, and refined subcategorization. Therefore, further refinement should be considered during the next revision.