Changes in the Updated 2016: WHO Classification of the Myelodysplastic Syndromes and Related Myeloid Neoplasms

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In comparison with the 2008 World Health Organization “Blue Book” on hematopoietic neoplasms, a small number of changes have been made in the classification. In the lower-risk patients, Refractory Cytopenias with Multilineage Dysplasia and Ring Sideroblasts (RCMD-RS) has been separated from RCMD to recognize the importance of the SF3B1 mutation. Often there has been confusion as to the degree of morphologic dysplasia and/or cytopenias to define some of the lower-risk subtypes. In addition, the type of dysplasia or cytopenias is not always concordant. Therefore, it seems prudent to apply the more general term “myelodysplastic syndrome (MDS)” with single- or multiple-lineage dysplasia. Refractory neutropenia or thrombocytopenia has been deemphasized because most patients have multilineage dysplasia. In the higher-risk patients, the terms Refractory Anemia with Excess Blasts (RAEB) 1 or 2 have been simplified to Myelodysplastic Syndrome-Excess Blasts (MDS-EB) 1 or 2 to emphasize the importance of the percentage of blasts that dictate therapy. Patients with Chronic Myelomonocytic Leukemia (CMML) can be classified into 3 groups: CMML 0, 1, or 2, based on the percentage of blasts (< 5%, 5%-9%, 10%-19%). Cases with 50% or more erythroid precursors will not have the percentage of blasts based on the nonerythroid precursors. Previous cases of acute erythroid leukemia (myeloid:erythroid type) can be included in the acute myeloid leukemia (AML) subtype: AML with MDS-related features.

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