World Health Organization (WHO) Classification of Myelodysplastic Syndromes/Neoplasms
| Name | WHO Estimated Proportion of Patients with MDS | Peripheral Blood: Key Features | Bone Marrow: Key Features |
|---|---|---|---|
| Refractory cytopenias with unilineage dysplasia (RCUD): | |||
| Refractory anemia (RA) | 10-20% | Anemia <1% of blasts | Unilineage erythroid dysplasia (in ≥10% of cells) <5% blasts |
| Refractory neutropenia (RN) | <1% | Neutropenia <1% blasts | Unilineage granulocytic dysplasia <5% blasts |
| Refractory thrombocytopenia (RT) | <1% | Thrombocytopenia <1% blasts | Unilineage megakaryocytic dysplasia <5% blasts |
| Refractory anemia with ring sideroblasts (RARS) | 3-11% | Anemia | Unilineage erythroid dysplasia ≥15% of erythroid precursors are ring sideroblasts <5% blasts |
| No blasts | |||
| Refractory cytopenias with multilineage dysplasia (RCMD) | 30% | Cytopenia(s) <1% blasts | Multilineage dysplasia ± ring sideroblasts <5% blasts |
| No Auer rods | No Auer rods | ||
| Refractory anemia with excess blasts, type 1 (RAEB-1) | 40% | Cytopenia(s) <5% blasts | Unilineage or multilineage dysplasia |
| No Auer rods | |||
| Refractory anemia with excess blasts, type 2 (RAEB-2) | Cytopenia(s) 5-19% blasts | Unilineage or multilineage dysplasia 10-19% blasts | |
| ± Auer rods | ± Auer rods | ||
| MDS associated with isolated del(5q) | Uncommon | Anemia | Isolated 5q31 chromosome deletion |
| Normal or high platelet count <1% blasts | Anemia; hypolobated megakaryocytes <5% blasts | ||
| Childhood MDS, including refractory cytopenia of childhood (provisional) (RCC) | 1 % | Pancytopenia | <5% marrow blasts for RCC |
| Marrow usually hypocellular | |||
| MDS, unclassifiable (MDS-U) | ? | Cytopenia ≤1% blasts | Does not fit other categories Dysplasia <5% blasts If no dysplasia, MDS-associated karyotype |
Note: If peripheral blood blasts are 2-4%, the diagnosis is RAEB-1 even if marrow blasts are <5%. If Auer rods are present, the WHO considers the diagnosis RAEB-2 if the blast proportion is <20% (even if <10%), AML if at least 20% blasts. For all subtypes, peripheral blood monocytes are <1 × 109/L. Bicytopenia may be observed in RCUD subtypes, but pancytopenia with unilineage marrow dysplasia should be classified as MDS-U. Therapy-related MDS (t-MDS), whether due to alkylating agents, topoisomerase II (t-MDS/t-AML) in the WHO classification of AML and precursor lesions. The listing in this table excludes MDS/myeloproliferative neoplasm overlap categories, such as chronic myelomonocytic leukemia, juvenile myelomonocytic leukemia, and the provisional entity RARS with thrombocytosis.
Abbreviation: MDS, myelodysplastic syndrome.