MDS subclassification—do we still have to count blasts?
Sandra Huber, Torsten Haferlach, Heiko Müller, Manja Meggendorfer, Stephan Hütter, Gregor Hoermann, Constance Baer, Wolfgang Kern, Claudia Haferlach
Abstract
Since their definition, the classification of myelodysplastic neoplasms (MDS) relied on cytomorphology determining dysplasia, cytopenia, and blast count [ 1 , 2 ]. The revised 4th edition of the WHO classification (WHO 2017) [ 3 ], encompasses only one genetically defined entity (MDS with isolated del(5q)). Since then, next-generation sequencing identified many driver genes in MDS [ 4 , 5 , 6 ]. Emphasizing a genetic basis for defining diseases, the 5th edition of the WHO classification (WHO 2022) [ 2 ] categorizes MDS into “morphologically-defined MDS” and “MDS with defining genetic abnormalities (DGA)”. WHO 2022 defines two additional MDS entities by genetics: MDS with low blasts and SF3B1 mutation and MDS with biallelic TP53 inactivation (bi TP53 ). All other cases are still classified based on cytomorphology into hypoplastic MDS, and MDS with low and increased blasts. The blast count as a crucial parameter to distinguish between MDS and AML has further been softened. In WHO 2022 the blast count cut-off has been eliminated if the criteria for AML-DGA are met, while according to the International Consensus Classification (ICC) [ 7 ] blast counts ≥10% are required. ICC introduced a new category MDS/AML for cases harboring 10–19% blasts. Thus, WHO 2022 and ICC use different bone marrow blast count cut-offs for defining myeloid diseases.