What are the types of the myelodysplastic syndromes?
Some types of MDS progress slowly, while others are more rapid. A classification system for the different types of MDS exists. It is based on the blood results, the appearance of the bone marrow and any chromosome changes found. The World Health Organization (WHO) classification of MDS is based on how the bone marrow looks and the number of leukaemia cells seen. These leukaemia cells are often called blasts. They refer to the youngest or most immature white blood cells. The number of blast cells is increased in some types of MDS and in leukaemia.
There are six types of MDS included in the WHO classification. You might also hear them referred to as subtypes. These are:
- Refractory cytopenia with unilineage dysplasia (RCUD)
- Refractory anaemia with ring sideroblasts (RARS)
- Refractory cytopenia with multilineage dysplasia (RCMD)
- Refractory anaemia with excess blasts (RAEB)
- Myelodysplastic syndrome unclassified (MDS-U)
- MDS associated with del 5q, including the 5q- syndrome
These names can sound confusing and hard to understand. But your doctor will explain which type of MDS you have in more detail. Cytopenias refer to the number of cell types that are low in your blood. Refractory anaemia means you have low red cell counts. Dysplasia refers to when the size, shape or look of blood cells are abnormal. Ring sideroblasts are red blood cells with ring-shaped iron deposits in them. MDS with deletion 5q means part of chromosome 5 is missing. Normally there are 23 pairs of chromosomes in your body.
CMML: Chronic myelomonocytic leukaemia (CMML) is sometimes considered a type of MDS. In CMML, one specific type of white cell is raised in your blood. These are the monocytes. The WHO classification puts CMML into a different group but it is still closely related. See page 00 for more details.
Low risk or high risk group
Sometimes it is easier to say if your type of MDS is high risk or low risk. The risk refers to your chance of developing acute myeloid leukaemia (AML) and how long you are expected to live.
Low risk: In this group, you have a 1 in 10 chance of developing AML. This includes the following types: RCUD, RCMD, RARS, MDS-U and the 5q- syndrome.
High risk: The risk of developing leukaemia is much higher in this group. This includes RAEB.
The treatment of low risk and high risk disease is often different. Your doctor may use the WHO classification to decide if your MDS if low risk or high risk, and also the International Prognostic Scoring System (IPSS). See page 00 for more details about IPSS.