Application of the International Consensus Classification and World Health Organization 5th edition classification to a series of myeloid neoplasms

Abstract

Abstract Objectives Two new classifications of myeloid neoplasms have recently been published: the International Consensus Classification (ICC) and the 5th edition of the World Health Organization classification (WHO5). We sought to examine the real-world impact of dueling classifications on patient diagnoses. Methods Our institutional pathology database was searched, and 237 specimens with a diagnosis of myeloid neoplasia were randomly selected. For each case, a classification based on the WHO5 and the ICC was assigned. The WHO5 and ICC diagnoses were compared to determine their degree of concordance. Results After applying the WHO5 and ICC diagnostic criteria, 134 (56.5%) cases were classified as concordant, 63 (26.6%) cases had terminological differences, 37 (15.6%) cases had minor diagnostic discrepancies, and 3 (1.3%) cases had major diagnostic discrepancies. Cases with minor diagnostic discrepancies included 25 cases of myelodysplastic syndrome (MDS), 10 cases of acute myeloid leukemia (AML), and 2 cases of myeloid precursor lesions. Cases with major diagnostic discrepancies included 2 cases that were diagnosed as MDS, not otherwise specified (NOS), according to the ICC but classified as AML with NPM1 alteration and AML with RBM15::MRTFA according to the WHO5 and 1 case that was characterized as chronic myelomonocytic leukemia according to the ICC and as AML with NPM1 alteration according to the WHO5. Conclusions This study confirms that a majority of cases are classified similarly using the 2 systems. Given the overall similarity of the systems, future harmonization of the classifications should be pursued to avoid confusion and multiple diagnoses.