who classsification of mds
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WHO 2022 classification myelodysplastic syndrome MDS ICC update
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WHO Classification of Myelodysplastic Syndromes (MDS)
Background
Myelodysplastic syndromes (MDS) are clonal hematopoietic neoplasms characterized by:
- Cytopenias due to ineffective hematopoiesis and increased apoptosis
- Morphologic dysplasia in one or more cell lineages
- Variable cytogenetic abnormalities
- Risk of progression to acute leukemia (AML)
WHO 2016 Classification (most widely used in practice)
The 2016 WHO classification recognizes 7 main subtypes:
1. MDS with Single-Lineage Dysplasia (MDS-SLD)
- Dysplasia in >10% of one myeloid lineage only
- Single-lineage cytopenia or bicytopenia
- Blasts: <1% blood, <5% marrow
- Includes pure erythroid dysplasia (refractory anemia), granulocytic dysplasia, and megakaryocytic dysplasia
- Good prognosis: median survival ≥5 years; AML progression only ~6%
2. MDS with Ring Sideroblasts (MDS-RS)
Two subcategories:
- MDS-RS-SLD: Ring sideroblasts ≥15% of erythroid precursors (or ≥5% if SF3B1 mutation present), single-lineage dysplasia, anemia
- MDS-RS-MLD: As above but with multilineage dysplasia
- SF3B1 mutation found in >80-90% of cases
- AML progression is very low (≤2%)
3. MDS with Multilineage Dysplasia (MDS-MLD)
- Dysplasia in ≥10% of precursors in two or more cell lines
- Bi- or pancytopenia
- Blasts: <1% blood, <5% marrow; no Auer rods
- Cytogenetic abnormalities in up to 50% (trisomy 8, monosomy 7, del(7q), del(5q), del(20q))
- Median survival ~36 months; AML progression 15% at 2 years, 28% at 5 years
4. MDS with Excess Blasts (MDS-EB)
Two subcategories:
- MDS-EB-1:
- Blood: cytopenia, <5% blasts, no Auer rods
- Marrow: 5-9% blasts, dysplasia in all 3 lines, frequent ALIP (abnormal localization of immature precursors)
- MDS-EB-2:
- Blood: >5% blasts, OR marrow 10-19% blasts, OR Auer rods present
- Survival usually <2 years; AML progression 25% (EB-1) and 33% (EB-2)
- Special variant: MDS-EB with fibrosis (MDS-EB-F) - increased dysplastic megakaryocytes + reticulin fibrosis
5. MDS with Isolated del(5q)
- Anemia ± thrombocytosis
- Isolated deletion of 5q (one additional abnormality allowed, except monosomy 7 or del[7q])
- Blasts: <1% blood, <5% marrow
- Small hypolobulated megakaryocytes are characteristic
- Good prognosis; responds to lenalidomide
6. MDS, Unclassifiable (MDS-U)
Three situations:
- MDS with 1% blood blasts (documented on two occasions)
- MDS-SLD with pancytopenia
- Persistent cytopenia with a defining cytogenetic abnormality but insufficient morphologic dysplasia
7. Refractory Cytopenia of Childhood (RCC) - Pediatric
- <5% blasts in marrow, <2% in blood
- Dysplasia + persistent cytopenia
- Marrow is often hypocellular (unlike adults)
WHO 2022 (5th Edition) - Key Updates
The 2022 WHO classification made two major structural changes:
-
Renamed "syndromes" to "neoplasms" - MDS is now officially "Myelodysplastic Neoplasms" (still abbreviated MDS)
-
Reorganized into two major groups:
- MDS with defining genetic abnormalities (e.g., MDS-SF3B1, MDS-TP53, MDS-5q, MDS with other defined genetic changes)
- MDS defined by morphology (with standardized morphologic criteria and fewer entities)
The International Consensus Classification (ICC) 2022 was published concurrently in Blood (Arber et al.) as a separate but related framework; experts recommend using both WHO 2022 and ICC 2022 complementarily, especially for SF3B1- and TP53-mutated MDS.
Summary Table (WHO 2016)
| Subtype | Blood Blasts | Marrow Blasts | Key Feature |
|---|---|---|---|
| MDS-SLD | <1% | <5% | 1 lineage dysplasia |
| MDS-RS-SLD | <1% | <5% | ≥15% ring sideroblasts, SF3B1 |
| MDS-MLD | <1% | <5% | ≥2 lineages dysplastic |
| MDS-RS-MLD | <1% | <5% | Ring sideroblasts + multilineage dysplasia |
| MDS-EB1 | <5% | 5-9% | No Auer rods |
| MDS-EB2 | ≥5% | 10-19% | ± Auer rods |
| MDS with del(5q) | <1% | <5% | Isolated del(5q), lenalidomide-sensitive |
| MDS-U | 1% (×2) | <5% | Doesn't fit other categories |
Sources:
- Henry's Clinical Diagnosis and Management by Laboratory Methods, pp. 742-743 - detailed subtype descriptions
- Goldman-Cecil Medicine, p. 1914 - unclassifiable MDS variants and CHIP
- WHO 2022 MDS reclassification overview - "myelodysplastic neoplasms" renaming and genetic grouping
- ICC vs WHO 2022 comparison
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