Doctors group myelodysplastic syndromes (MDS) into different groups and different risk groups.
MDS blood cells have changes in them that make them develop abnormal cells. They might not need treatment for many years, but some go on to develop into acute myeloid leukaemia (AML). This means that they are cancer but how they progress will depend on the type that you have and the risk of them going on to develop into AML.
World Health Organisation (WHO) system
There are different types of myelodysplastic syndrome. Some affect one type of blood cell, other myelodysplastic syndromes affect all types of blood cells.
MDS can develop slowly or quickly depending on the type you have.
Doctors divide the different types of MDS into groups or subtypes. The system they use is called a classification system. The most used classification system for MDS in the UK is the World Health Organisation (WHO) system. This generally looks at how many immature cells (blasts) there are in the blood and bone marrow, and how normal the cells are.
This is quite complicated, and your doctor or nurse can explain it in more detail.
You can read about the different types below.
Refractory cytopenia with unilineage dysplasia (RCUD)
This affects a single type of blood cell. It can be divided into 3 subtypes:
- refractory anaemia (RA) – low numbers of red blood cells
- refractory neutropenia (RN) – low numbers of white blood cells
- refractory thrombocytopenia (RT) – low numbers of platelets
Refractory anaemia with ring sideroblasts (RARS)
This is similar to refractory anaemia (RA). But there are a greater number of early red blood cells in the bone marrow that have a ring of iron in them. These cells are called ring sideroblasts.
Refractory cytopenia with multilineage dysplasia (RCMD)
The MDS affects more than one type of blood cell. So 2 or more of your blood cell levels will be low. There are very few or no immature cells (blasts) in the blood. There are a small number of blasts in the bone marrow.
Refractory anaemia with excess blasts (RAEB-1 and RAEB-2)
One or more of your blood cell levels are low, and many of these cells look abnormal in the bone marrow. There are a greater number of immature cells (blasts) in the blood and bone marrow.
RAEB is split into RAEB1 and RAEB2. In RAEB2, there are more blast cells in the blood and bone marrow than in RAEB1.
Myelodysplastic syndrome associated with isolated del (5q)
With this type, the cells in the bone marrow have a chromosome change called isolated del (5q). There are low numbers of red cells in the blood (anaemia). The platelet count is usually normal or high.
Myelodysplastic syndrome unclassified (MDS-U)
This covers any type of MDS that does not fit into one of the above groups.
Risk groups for MDS
As well as the different types of MDS, doctors group them according to how the disease is most likely to develop.
In some people, MDS will develop into a type of cancer of the blood called acute myeloid leukaemia (AML). Doctors call this transformation. Some types of MDS have a higher risk of transforming into AML than others. The risk varies from around 5 in every 100 cases (5%) to 65 out of every 100 cases (65%), depending on the type of MDS.
Transformation might happen after a few months for some types of MDS but after several years for others. You can ask your doctor about the risk of transformation with your type of MDS.
The system for grouping MDS according to likely outcome is called the Revised International Prognostic Scoring System (IPSS-R). There are 5 risk groups:
- very low risk
- low risk
- intermediate risk
- high risk
- very high risk
The risk group depends on:
- the number of immature cells (blasts) in your bone marrow and blood
- your blood cell levels
- whether there are chromosome changes in the affected blood cells
Knowing what type of MDS you have and your risk score helps your doctor to decide on the best treatment for you.