Myelodysplastic Syndrome (MDS)

Table of Contents

1. What is Myelodysplastic Syndrome?
2. WHO 2022 Classification
3. Pathophysiology and Clonal Hematopoiesis
4. Symptoms and Clinical Presentation
5. Diagnosis and Workup
6. IPSS-R Risk Stratification
7. Treatment: Low-Risk MDS
8. Treatment: High-Risk MDS
9. Complications and Prognosis
10. Research Papers
11. Connections
12. Featured Videos

What is Myelodysplastic Syndrome?

Myelodysplastic Syndrome (MDS) is a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, peripheral blood cytopenias, dysplastic morphology of bone marrow cells, and a variable risk of transformation to acute myeloid leukemia (AML). MDS affects primarily older adults — median age at diagnosis is 70 years — and carries a spectrum of outcomes ranging from indolent disease manageable with supportive care to aggressive disease requiring intensive therapy.

Approximately 10,000–15,000 new MDS cases are diagnosed annually in the United States. The hallmark is a discrepancy between a hypercellular (or normocellular) bone marrow that is producing cells abundantly but ineffectively, and a peripheral blood count that shows cytopenias because most developing cells die before maturation — a process called intramedullary apoptosis.

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WHO 2022 Classification

The 2022 WHO Classification of Haematolymphoid Tumours reorganized MDS away from morphology-only subtyping toward an integrated molecular framework. Key entities include:

MDS with Defining Genetic Abnormalities

• MDS-SF3B1: Harbors SF3B1 mutation; characterized by ring sideroblasts (≥15% or ≥5% if SF3B1 mutated), typically low-risk biology with favorable prognosis. Ring sideroblasts reflect abnormal iron loading of mitochondria in erythroid precursors.
• MDS with del(5q) [MDS-5q]: Isolated deletion of chromosome 5q31–33; predominantly affects older women; macrocytic anemia with normal or elevated platelet count; highly responsive to lenalidomide.
• MDS-TP53: Biallelic TP53 mutations or single mutation with loss of heterozygosity; associated with complex karyotype; poor prognosis and high AML transformation rate; often therapy-related.
• MDS-RUNX1, MDS-ETV6, MDS-GATA2: Newly recognized entities with specific germline or somatic driver mutations conferring distinct clinicopathologic features.

MDS with Morphological Features (without defining genetics)

• MDS with low blasts (MDS-LB): Bone marrow blasts <5%, replaces MDS-MLD and most MDS-SLD from prior classification.
• MDS with increased blasts (MDS-IB): MDS-IB1 (5–9% BM blasts or 2–4% PB blasts) and MDS-IB2 (10–19% BM blasts or 5–19% PB blasts, or Auer rods); higher AML transformation risk.
• MDS, hypoplastic: Hypocellular marrow (<25% cellularity), may overlap with aplastic anemia.

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Pathophysiology and Clonal Hematopoiesis

MDS originates from a somatic mutation in a hematopoietic stem cell that confers a clonal survival advantage. Over time, additional mutations accumulate (clonal evolution), progressively impairing differentiation and increasing blast counts. The most frequently mutated genes include:

• Splicing factors: SF3B1 (25–30%), SRSF2 (15%), U2AF1 (10%), ZRSR2 (5%) — disrupt pre-mRNA splicing.
• Epigenetic regulators: TET2 (25%), DNMT3A (15%), ASXL1 (15%), EZH2 (5%) — alter DNA methylation and chromatin state.
• Transcription factors: RUNX1, ETV6, GATA2.
• Tumor suppressors: TP53 (5–10% de novo, higher in therapy-related MDS).

The bone marrow microenvironment contributes through excess TNF-α and TGF-β signaling, which promote apoptosis of dysplastic progenitors despite cellular overproduction. This explains the paradox of hypercellular marrow with peripheral cytopenias. Activation-induced apoptosis via Fas/FasL pathways is particularly prominent in early MDS.

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Symptoms and Clinical Presentation

Most MDS patients present with symptoms related to cytopenias rather than the underlying clonal disorder itself:

• Anemia (most common, ~85%): Fatigue, dyspnea on exertion, pallor, palpitations. Often macrocytic (MCV >100 fL) due to dyserthropoiesis, mimicking B12 or folate deficiency.
• Neutropenia (~50%): Recurrent bacterial infections, particularly of the skin and respiratory tract. Absolute neutrophil count (ANC) <1.0 ×10⁹/L significantly increases infection risk.
• Thrombocytopenia (~25–50%): Easy bruising, petechiae, mucosal bleeding, epistaxis. Platelet dysfunction can occur even when counts are near-normal.
• Pancytopenia: Combination of all three lineage failures; associated with more advanced disease.
• Asymptomatic incidental discovery: Increasingly common as routine bloodwork detects cytopenias during evaluation for unrelated conditions.

Constitutional symptoms (fever, night sweats, weight loss) are uncommon in low-risk MDS but may herald progression to higher-risk disease or AML transformation.

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Diagnosis and Workup

Diagnosis of MDS requires integration of peripheral blood findings, bone marrow morphology, cytogenetics, and molecular profiling. There is no single diagnostic test.

Essential Workup

• Complete blood count with differential: Cytopenias in one or more lineages; dysplastic forms (pseudo-Pelger-Huet neutrophils, hypogranular neutrophils, giant platelets) visible on smear review.
• Reticulocyte count: Inappropriately low for degree of anemia (reflects inadequate erythropoietic response).
• Bone marrow aspiration and biopsy: Essential for diagnosis. Dysplasia must affect ≥10% of cells in any lineage; ring sideroblast count by Prussian blue iron stain; blast percentage by morphology (and confirmed by flow cytometry).
• Conventional cytogenetics (karyotype): Abnormal in ~50% of de novo MDS and >80% of therapy-related MDS. Common abnormalities: del(5q), del(7q)/-7, +8, del(20q), complex karyotype (≥3 abnormalities).
• Fluorescence in situ hybridization (FISH): Detects del(5q), del(7q), +8, del(20q) when karyotype fails or metaphases are inadequate.
• Next-generation sequencing (NGS) panel: Identifies somatic mutations in SF3B1, TET2, ASXL1, SRSF2, TP53, DNMT3A, RUNX1, and others; now integrated into WHO 2022 classification and IPSS-M risk model.

Exclusion of Mimics

Reversible causes of dysplasia and cytopenia must be excluded before diagnosing MDS: vitamin B12 and folate deficiency, copper deficiency, alcohol toxicity, HIV infection, heavy metal exposure (arsenic), thyroid dysfunction, and certain medications (mycophenolate, methotrexate).

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IPSS-R Risk Stratification

The Revised International Prognostic Scoring System (IPSS-R) is the standard tool for predicting overall survival and AML transformation risk. It incorporates five variables, each weighted:

• Cytogenetic risk group: Very good (e.g., -Y, del(11q)) / Good (normal, del(5q), del(20q), del(12p)) / Intermediate (del(7q), +8, +19, i(17q)) / Poor (-7, inv(3)/t(3q)/del(3q), complex with 3 abnormalities) / Very poor (complex with >3 abnormalities).
• Bone marrow blast %: ≤2% (0 pts), >2–<5% (1 pt), 5–10% (2 pts), >10% (3 pts).
• Hemoglobin: ≥10 g/dL (0 pts), 8–<10 (1 pt), <8 (1.5 pts).
• Platelet count: ≥100 ×10⁹/L (0 pts), 50–<100 (0.5 pts), <50 (1 pt).
• ANC: ≥0.8 ×10⁹/L (0 pts), <0.8 (0.5 pts).

IPSS-R Risk Categories and Median Overall Survival

• Very Low (≤1.5): Median OS ~8.8 years; AML transformation at 25% threshold ~14.5 years.
• Low (>1.5–3): Median OS ~5.3 years; AML transformation ~10.8 years.
• Intermediate (>3–4.5): Median OS ~3.0 years; AML transformation ~3.2 years.
• High (>4.5–6): Median OS ~1.6 years; AML transformation ~1.4 years.
• Very High (>6): Median OS ~0.8 years; AML transformation ~0.7 years.

The molecular IPSS-M (IPSS-Molecular), published in 2022, incorporates 31 gene mutation variables and refines risk prediction beyond IPSS-R alone. An online calculator is available at mds-risk-model.com.

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Treatment: Low-Risk MDS

For patients with IPSS-R very low or low risk, the primary treatment goal is improving quality of life and managing cytopenias rather than altering disease course. Watchful waiting is appropriate for asymptomatic patients without significant cytopenias.

Anemia Management

• Erythropoiesis-stimulating agents (ESAs): Epoetin alfa or darbepoetin alfa are first-line for transfusion-dependent or symptomatic anemia when serum EPO level is <500 mU/mL and ring sideroblasts are absent or low (<15%). Response rates ~40–60%; duration of response typically 18–24 months.
• Luspatercept (Reblozyl): TGF-β superfamily ligand trap approved for ESA-refractory ring sideroblast MDS (MDS-SF3B1). The MEDALIST trial demonstrated 38% transfusion independence rate vs 13% placebo. Now also FDA-approved as first-line therapy for low-risk MDS-associated anemia (2023 approval based on COMMANDS trial).
• Red blood cell transfusions: Threshold typically hemoglobin <8 g/dL or symptomatic. Chronic transfusion leads to iron overload; ferritin >1000 ng/mL warrants chelation consideration.
• Iron chelation: Deferasirox (Exjade) or deferoxamine for transfusion iron overload in patients with good performance status and expected survival >1 year.

Lenalidomide for del(5q) MDS

Lenalidomide is the standard treatment for transfusion-dependent del(5q) MDS. The MDS-003 and MDS-004 trials demonstrated transfusion independence in ~67% of patients and cytogenetic response in ~45%. Starting dose 10 mg/day. Main toxicities: neutropenia and thrombocytopenia (dose reduction often required). Monitoring for TP53 clonal evolution during lenalidomide therapy is recommended.

Immunosuppressive Therapy

Antithymocyte globulin (ATG) ± cyclosporine benefits a subset of younger patients (<60 years) with hypoplastic MDS, normal karyotype, and HLA-DR15 positivity — overlapping with aplastic anemia biology. Response rates ~30–40%.

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Treatment: High-Risk MDS

For IPSS-R intermediate, high, or very high risk MDS, the goals shift toward disease modification and, where possible, curative allogeneic stem cell transplantation.

Hypomethylating Agents (HMAs)

• Azacitidine (Vidaza): First approved HMA; inhibits DNA methyltransferases, restoring expression of silenced tumor suppressor genes. The AZA-001 trial demonstrated superior overall survival vs conventional care regimens (24.5 vs 15 months; HR 0.58). Schedule: 75 mg/m²/day × 7 days every 28 days. Response requires minimum 6 cycles; continue until disease progression.
• Decitabine (Dacogen): Alternative HMA with similar mechanism; comparable efficacy. Decitabine/cedazuridine (Inqovi) is an oral formulation producing bioequivalent plasma levels, improving patient convenience.
• Venetoclax combinations: BCL-2 inhibitor venetoclax plus azacitidine, proven in AML, is being investigated in MDS-IB2; promising early data, not yet standard of care for MDS.

Allogeneic Hematopoietic Stem Cell Transplantation (HSCT)

The only potentially curative therapy for MDS. Indicated for eligible patients with IPSS-R ≥3.5 (intermediate to very high risk) and adequate organ function. Key considerations:

• Age and comorbidities: Reduced-intensity conditioning (RIC) regimens have extended eligibility to patients up to age 75 with acceptable comorbidity burden.
• Donor source: Matched sibling donor preferred; matched unrelated donor (10/10 HLA match) is equivalent; haploidentical transplant acceptable when no matched donor available.
• Pretransplant cytoreduction: HMA therapy used to reduce blast count before transplant; debate remains whether achieving complete remission improves post-transplant outcomes.
• TP53-mutated MDS: Poor outcomes with standard transplant conditioning; ongoing trials with TP53-directed agents (eprenetapopt/APR-246) in combination with transplant conditioning.
• Post-transplant maintenance: Azacitidine maintenance post-transplant reduces relapse risk (RELAZA2 trial).

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Complications and Prognosis

• AML transformation: Risk ranges from <5% in IPSS-R very low to >50% in very high risk at 5 years. Acquisition of additional mutations in RAS/NRAS, FLT3, or TP53 often heralds transformation.
• Infection: Leading cause of death in lower-risk MDS; neutropenic infections require prompt broad-spectrum antibiotics.
• Transfusion iron overload: Hepatic and cardiac iron deposition in chronically transfused patients; assessed by serum ferritin and MRI T2* imaging.
• Cardiovascular events: Chronic anemia exacerbates underlying cardiovascular disease, the primary comorbidity in the MDS age group.
• Therapy-related MDS: Occurs 5–10 years after cytotoxic chemotherapy or radiation for prior malignancy; characterized by complex karyotype, TP53 mutations, and aggressive biology.

Prognosis varies dramatically by risk group. Low-risk patients may live 5–10+ years without intensive therapy, while very-high-risk patients have median survival under 1 year without transplant.

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Research Papers

The following PubMed links return current peer-reviewed literature on myelodysplastic syndrome. Each opens a live search.

• Greenberg et al. (2012) IPSS-R — PMID 22776782
• Fenaux et al. (2009) AZA-001 azacitidine vs CCR — PMID 20485435
• List et al. (2006) lenalidomide del(5q) MDS-003 — PMID 16714769
• Bejar et al. (2017) SF3B1 mutations in MDS — PMID 27907888
• Platzbecker et al. (2020) luspatercept MEDALIST — PMID 32187361
• Bernard et al. (2022) IPSS-M molecular model — PMID 35353940
• Zeidan et al. (2022) WHO 2022 MDS classification — PMID 36332555
• Sekeres et al. (2009) ESA therapy low-risk MDS — PMID 19654408
• Duncavage et al. (2019) NGS in MDS diagnosis — PMID 31395601
• Jädersten & Hellström-Lindberg (2022) TP53-mutated MDS — PMID 35235960
• Ades et al. (2018) allogeneic HSCT in MDS — PMID 30025150
• García-Manero et al. (2021) decitabine/cedazuridine oral HMA — PMID 33956590

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Connections

• Anemia
• Acute Myeloid Leukemia
• Thrombocytopenia
• Sickle Cell Disease
• Thalassemia
• Hemophilia
• Hemochromatosis
• Deep Vein Thrombosis
• Disseminated Intravascular Coagulation
• Complete Blood Count
• Iron
• Folate
• Heart Failure
• Fatigue
• Pulmonary Hypertension
• Chronic Myeloid Leukemia

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