Differences in classification schemata for myelodysplastic/myeloproliferative overlap neoplasms

Comparing malignant monocytosis across the updated WHO and ICC classifications of 2022

ABSTRACT

The World Health Organization (WHO) classification of hematolymphoid tumors and the International Consensus Classification (ICC) of 2022 introduced major changes to the definition of chronic myelomonocytic leukemia (CMML). To assess its qualitative and quantitative implications for patient care, we started with 3311 established CMML cases (according to WHO 2017 criteria) and included 2130 oligomonocytosis cases fulfilling the new CMML diagnostic criteria. Applying both 2022 classification systems, 356 and 241 of oligomonocytosis cases were newly classified as myelodysplastic (MD)-CMML (WHO and ICC 2022, respectively), most of which were diagnosed as myelodysplastic syndrome (MDS) according to the WHO 2017 classification. Importantly, 1.5 times more oligomonocytosis cases were classified as CMML according to WHO 2022 than based on ICC, because of different diagnostic criteria. Genetic analyses of the newly classified CMML cases showed a distinct mutational profile with strong enrichment of MDS-typical alterations, resulting in a transcriptional subgroup separated from established MD and myeloproliferative CMML. Despite a different cytogenetic, molecular, immunophenotypic, and transcriptional landscape, no differences in overall survival were found between newly classified and established MD-CMML cases. To the best of our knowledge, this study represents the most comprehensive analysis of routine CMML cases to date, both in terms of clinical characterization and transcriptomic analysis, placing newly classified CMML cases on a disease continuum between MDS and previously established CMML.

Myeloid madness: assessing diagnostic inconsistency between the new WHO and ICC schemes for myelodysplastic/myeloproliferative neoplasms

The classification of haematological neoplasms recently underwent revision, generating two separate schemes-the International Consensus Classification and the fifth edition of the WHO classification. The new division into separate classification systems presents challenges for haematopathologists, haematologists/oncologists and patients. While it is too early to assess the full clinical impact, we sought to identify diagnostic discordance which may arise from applying separate classification schemes in myeloid neoplasia, and particularly in the challenging category of myelodysplastic syndrome/myeloproliferative neoplasms. A review of 64 such cases found 1 case with a significant discrepancy between the WHO and International Consensus Classification systems, and 9 cases with nominal discrepancies. Confusion from the use of conflicting diagnostic terms represents a potential source of patient harm, increased pathologist workload and burnout and erosion of clinician and patient trust.