Table 1.

2008 World Health Organization classification of myelodysplastic syndromes/neoplasms

Name	Abbreviation	Peripheral blood: key features	Bone marrow: key features	WHO estimated proportion of patients with MDS
Refractory cytopenias with unilineage dysplasia (RCUD):
refractory anemia	RA	Anemia <1% blasts	Unilineage erythroid dysplasia (in 10% of cells) <5% blasts	10–20%
refractory neutropenia	RN	Neutropenia <1% blasts	Unilineage granulocytic dysplasia <5% blasts	<1%
refractory thrombocytopenia	RT	Thrombocytopenia <1% blasts	Unilineage megakaryocytic dysplasia <5% blasts	<1%
Refractory anemia with ring sideroblasts	RARS	Anemia No blasts	Unilineage erythroid dysplasia 15% of erythroid precursors are ring sideroblasts <5% blasts	3–11%
Refractory cytopenias with multilineage dysplasia	RCMD	Cytopenia(s) <1% blasts No Auer rods	Multilineage dysplasia ± ring sideroblasts <5% blasts No Auer rods	30%
Refractory anemia with excess blasts, type 1	RAEB-1	Cytopenia(s) <5% blasts No Auer rods	Unilineage or multilineage dysplasia 5–9% blasts No Auer rods	40%
Refractory anemia with excess blasts, type 2	RAEB-2	Cytopenia(s) 5–19% blasts ±Auer rods	Unilineage or multilineage dysplasia 10–19% blasts ±Auer rods
MDS associated with isolated del(5q)	Del(5q)	Anemia Normal or high platelet count <1% blasts	Isolated 5q31 chromosome deletion Anemia, hypolobated megakaryocytes <5% blasts	Uncommon
Childhood MDS, including refractory cytopenia of childhood (provisional)	RCC	Pancytopenia	<5% marrow blasts for RCC Marrow usually hypocellular	<1%
MDS, unclassifiable	MDS-U	Cytopenias 1% blasts	Does not fit other categories Dysplasia and <5% blasts If no dysplasia, MDS-associated karyotype	?

Adapted from Steensma et al. [2009].

If peripheral blood blasts are 2–4%, the diagnosis is RAEB-1 even if marrow blasts are less than 5%. If Auer rods are present, the WHO considers the diagnosis RAEB-2 if the blast proportion is less than 20% (even if less than 10%), AML if at least 20% blasts. For all subtypes, peripheral blood monocytes are less than 1 × 10⁹/liter. 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 inhibitors, or radiation, is classified together with therapy-related acute myeloid leukemia (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.

MDS, myelodysplastic syndromes; WHO, World Health Organization.