The New WHO Classification – What to Expect

In the myeloid neoplasia group, precursor lesions were included as entities for the first time: clonal hematopoiesis with a special definition of clonal hematopoiesis of indeterminate potential (CHIP) and clonal cytopenia of undetermined significance (CCUS) This has produced a globally uniform definition, which will allow better comparability for future studies.

Myelodysplastic syndrome has been renamed myelodysplastic neoplasia to make it clear in the name as well that it is a neoplasia and to harmonize with myeloproliferative neoplasia (still myeloproliferative diseases/syndromes in 2001) – however, the abbreviation MDS will be kept. MDS is further divided into two major groups: MDS with defining genetic abnormalities and MDS defined by morphology, whereby the morphological criteria have been standardized and the number of entities reduced.

In acute myeloid leukemias, AML with defining genetic abnormalities are distinguished from AML defined by differentiation, which are classified based on morphology.The number of genetically defined entities has once again increased compared to the 2017 version. Genetic differentiation in myeloid/lymphoid neoplasia with eosinophilia has been refined as well.

While genetic parameters are still not being used for classifying T-lymphoblastic leukemia, several new genetically defined subtypes have been added for B-lymphoblastic leukemia. The latest findings of transcriptome sequencing have already been taken into account here. It is therefore necessary to incorporate RNA sequencing in the routine diagnosis of B-cell line ALL. MLL will be proposing a diagnostic algorithm for this purpose. The vast majority of lymphoma entities continue to be defined histologically and by their immunophenotype.

MLL is currently making all of the preparations necessary for diagnosing according to the new WHO classification. It helps that, for each entity, both the essential as well as the desirable diagnostic criteria have been defined very specifically by the WHO. As soon as the 5th edition of the WHO classification is published in its entirety as an online book – probably in fall 2022 – we will also implement it in our diagnostic reports. To make the transition as easy as possible for all of us, we will be holding several training sessions on this topic. The first seminar will be held on 07/27/2022, 4:00 - 6:00 p.m. on site at MLL. Participating virtually will be possible as well. We will also provide detailed information about the new WHO classification on our mll.com website.

As far as we are concerned, the update of the WHO classification represents a major step forward, as this makes a more detailed biological definition of the entities possible, taking into account the genetic parameters. This is the most important prerequisite for personalized medicine.