WHO MDS
CLASSIFICATION SUBTYPES
World Health Organization (WHO) Classification Subtypes*
The most current system for classifying leukemia and myelodysplastic syndromes (MDS), it was developed by the World Health Organization (WHO). This system is based on patient data from around the world and on the most up-to-date knowledge of MDS. WHO Classification of MDS consists of many subtypes based on tests of the blood and bone marrow.
Knowing your MDS subtype can guide discussions with your healthcare team about the best treatment options for you.
2016 WHO CLASSIFICATION SYSTEM
The WHO classification of MDS was updated in 2016. The categories are largely based on morphology (how the cells look under the microscope), the presence of blasts (immature cells), how many cell lines are involved, and specific cytogenetic or molecular findings. The current classification of MDS includes:
| 2016 Classification | ||
|---|---|---|
| MDS | MDS-SLD with ring sideroblasts | MDS-EB2 |
| MDS-SLD | MDS-MLD with ring sideroblasts | MDS with isolated del(5q) |
| MDS-MLD | MDS-EB1 | MDS-U (MDS, unclassifiable) |
2022 WHO CLASSIFICATION SYSTEM
The WHO classification of MDS was updated again in 2022. The WHO classification system for MDS has proposed the new term, Myelodysplastic Neoplasms (still abbreviated MDS) to reflect the malignant nature of MDS. This revised classification system divides MDS into two major groups:
- MDS with defining genetic abnormalities
- MDS that are morphologically defined (how the cells look under the microscope). The threshold for dysplastic changes in all cell lines has been set at >10%.
There may be some overlap of terms while providers are transitioning from one update to the next.
2022 CLASSIFICATION AND DEFINING FEATURES OF MYELODYSPLASTIC NEOPLASM (MDS)
| MDS with defining genetic abnormalities | Blasts | Cytogenetics | Mutations |
|---|---|---|---|
| MDS with low blasts and isolated 5q deletion (MDS-5q) | <5% bone marrow and <2% peripheral blood | 5q deletion alone, or with 1 other abnormality other than monosomy 7 or 7q deletion | |
| MDS with low blasts and SF3B1 mutation (MDS-SF3B1) | Absence of 5q deletion, monosomy 7, or complex karyotype | SF3B1 Detection of ≥15% ring sideroblasts may substitute for SF3B1 mutation | |
| MDS with biallelic* TP53 inactivation (MDS-biTP53) | <20% bone marrow and peripheral blood | Usually, complex | Two or more TP53 mutations, or 1 mutation with evidence of TP53 copy number loss* or cnLOH* |
| MDS, Morphologically Defined | Blasts |
|---|---|
| MDS with low blasts (MDS-LB) | <5% bone marrow and <2% peripheral blood |
| MDS, hypoplastic* (MDS-h) (≤25% age adjusted bone marrow cellularity) | N/A |
| MDS with increased blasts (MDS-IB) | |
| MDS-IB1 | 5–9% bone marrow or 2–4% peripheral blood |
| MDS-IB2 | 10-19% bone marrow or 5–19% peripheral blood or Auer rods |
| MDS with fibrosis | 5–19% bone marrow; 2–19% peripheral blood |
*DEFINITIONS
Copy number loss – loss of gene copies of from a normal genome
Biallelic – affecting both alleles of a gene
cnLOH – Copy neutral loss of heterozygosity (cnLOH) is an acquired
abnormality found in patients with cancer and hematologic disorders
that refers to a special case of LOH occurring without any resulting loss in
copy number.
Allele – An allele is a variant form of a gene that has a different effect on the organism’s appearance and function
Hypoplastic (hypocellular) – there are too few cells within the bone
marrow