There are several kinds (subtypes) of MDS. Doctors classify MDS subtypes according to different factors. Doctors often use one of two systems to classify them: the French, American, British (FAB) classification system or World Health Organization (WHO) classification system.
The classification of MDS has evolved considerably over the last several decades. In 1982, the French-American-British (FAB) Work Group devised a classification of MDS. In 2001, the World Health Organization (WHO) proposed an alternative classification that was modified from the original FAB and that incorporated molecular and cytogenetic factors. Since then, the WHO classification has been updated twice, once in 2008 and again in 2016.
Doctors also use the International Prognostic Scoring System (IPSS) to more narrowly define the degree of the disease's severity, determine patient risk factors and plan treatment.
FAB Classification
The FAB classification divided MDS into five subtypes based on the percentage of blasts in the bone marrow and the peripheral blood, the number of ring sideroblasts (RS) and the degree of monocytosis (elevated number of white blood cells) as follows:
- Refractory anemia (RA)
- Refractory anemia with ringed sideroblasts (RARS)
- Refractory anemia with excess blasts (RAEB)
- Refractory anemia with excess blasts in transformation (RAEB-T)
- Chronic myelomonocytic leukemia (CMML)
WHO Classification
The current WHO classification guidelines identify six subtypes of MDS based on the results of blood and bone marrow test. It classifies MDS according to factors that differ from those of the FAB system:
- MDS with single lineage dysplasia (MDS-SLD)
- Refractory anemia (RA)
- Refractory neutropenia (RN)
- Refractory thrombocytopenia (RT)
- MDS with ring sideroblasts (MDS-RS)
- Single lineage dysplasia (MDS-RS-SLD)
- Multilineage dysplasia (MDS-RS-MLD)
- MDS with multilineage dysplasia (MDS-MLD)
- MDS with excess blasts (MDS-EB)
- MDS with excess blasts-1 (MDS-EB-1)
- MDS with excess blasts-2 (MDS-EB-2)
- MDS with isolated del(5q)
- MDS unclassifiable
Related Links
- International Prognostic Scoring System (IPSS)
- Download or order The Leukemia & Lymphoma Society's free booklet, Myelodysplastic Syndromes.