Myelodysplastic Syndromes

Myelodysplastic syndromes are a group of clonal bone marrow disorders in which hematopoietic stem cells produce blood cells that mature abnormally and die prematurely, so that the marrow is typically cellular yet the blood shows one or more cytopenias. They are defined by morphologic dysplasia together with recurrent genetic lesions, and they carry a variable risk of progression to acute myeloid leukemia.

Definition

Myelodysplastic syndromes are clonal hematopoietic stem-cell neoplasms characterized by morphologically dysplastic, ineffective blood-cell production resulting in peripheral cytopenias, recurrent cytogenetic and molecular abnormalities, and an increased risk of transformation to acute myeloid leukemia.

Scope

This entry covers the defining features of the myelodysplastic syndromes: the concept of dysplasia and ineffective hematopoiesis, the genetic landscape, the World Health Organization classification, and the prognostic scoring systems used to stratify risk. It is a reference and educational entry on the disease itself, not a guide to selecting therapy.

Key concepts

• Dysplasia
• Ineffective hematopoiesis
• Peripheral cytopenia with cellular marrow
• Blast percentage
• Recurrent cytogenetic abnormalities (e.g., del(5q))
• Somatic mutations (SF3B1, TET2, ASXL1, TP53, and others)
• Risk of progression to acute myeloid leukemia
• Prognostic scoring (IPSS, IPSS-R)

Mechanisms

A founding mutation in a hematopoietic stem cell establishes a clone whose progeny mature defectively. Mutations cluster in genes governing RNA splicing (such as SF3B1), DNA methylation and chromatin (such as TET2 and ASXL1), transcription, and the DNA-damage response (such as TP53), and their pattern shapes both phenotype and outcome (Bejar, 2011). The dysplastic precursors undergo excessive intramedullary apoptosis, producing the paradox of a cellular or hypercellular marrow with low peripheral counts. As clones acquire additional lesions and the blast fraction rises, the disorder can evolve toward acute myeloid leukemia, which is why blast percentage and cytogenetics are central to classification and risk assessment (Arber, 2016; Khoury, 2022).

Clinical relevance

Myelodysplastic syndromes are an important cause of otherwise unexplained anemia, neutropenia, or thrombocytopenia in older adults, and recognizing dysplasia and clonal markers distinguishes them from reactive or nutritional cytopenias. This entry explains the disease and its risk stratification for reference; it does not provide treatment thresholds or management advice for individuals.

Epidemiology

Myelodysplastic syndromes are diseases of later life, with median age at diagnosis in the early-to-mid seventies and incidence rising steeply with age; they are somewhat more common in men. Prior cytotoxic chemotherapy or radiation is a recognized risk factor for therapy-related disease, which tends to carry a poorer prognosis.

Evidence & guidelines

The World Health Organization classification, revised in 2016 and again in the 2022 fifth edition, defines the subtypes by dysplasia, blast count, cytogenetics, and defining mutations (Arber, 2016; Khoury, 2022). Prognosis is most widely stratified with the International Prognostic Scoring System and its revised form, which combine marrow blasts, cytogenetic risk, and the depth of cytopenias (Greenberg, 1997; Greenberg, 2012); molecular data such as TP53 and other mutations add further prognostic information (Bejar, 2011).

History

The myelodysplastic syndromes were first organized by the French-American-British cooperative group, which defined subtypes by morphology and blast count and replaced the older term preleukemia. The World Health Organization later integrated cytogenetics and then molecular genetics into the scheme. Prognostic stratification advanced with the 1997 International Prognostic Scoring System and its 2012 revision, while large sequencing studies clarified the mutational basis of the diseases (Greenberg, 1997; Greenberg, 2012; Bejar, 2011).

Debates

How should molecular data be integrated into prognosis?

Classical scoring systems rest on blast count, cytogenetics, and cytopenias, but somatic mutations such as TP53 carry independent prognostic weight, raising the question of how best to combine morphologic, cytogenetic, and molecular information into a unified risk model.

Key figures

• Peter Greenberg
• Rafael Bejar
• Pierre Fenaux
• Mario Cazzola
• Daniel Arber

Seminal works

• greenberg-1997
• greenberg-2012
• bejar-2011
• arber-2016

Frequently asked questions

Why are blood counts low if the bone marrow is full of cells?

In myelodysplastic syndromes the marrow produces cells, but they are dysplastic and die before reaching the bloodstream, a process called ineffective hematopoiesis, so the marrow can be cellular while peripheral counts are low.

Do all myelodysplastic syndromes become leukemia?

No. The risk of transformation to acute myeloid leukemia varies widely by subtype, blast count, cytogenetics, and molecular features, and many lower-risk cases never progress.