What are myelodysplastic syndromes (MDS)?

Other names for MDS

Myelodysplastic syndromes are also called myelodysplasia, myelodysplastic neoplasms, or MDS for short. You may also hear them called myelodysplastic disorders. 'Myelo' means bone marrow and 'dysplasia' means abnormal growth.

What happens in MDS?

In MDS the bone marrow doesn’t work properly causing a drop in the number of normal blood cells. This means the blood cells don’t work as well as they should. This can lead to problems such as ​anaemia​, bleeding or infections.

Some people with MDS go on to develop acute myeloid leukaemia (AML). How they progress depends on:  

• the type of MDS

• the risk of that type changing into AML

MDS can happen in people of any age, but they are most common in people over 75 years old. They are more common in men.

About the bone marrow and blood cells

To understand more about MDS, it helps to know how you make blood cells.

The bone marrow is the soft inner part of our bones that makes blood cells. All blood cells start from the same type of cell called a stem cell. The stem cell makes immature blood cells. The immature cells go through various stages of development before they are released into the blood as fully developed blood cells.

These include:

• red blood cells to carry oxygen around our bodies

• white blood cells to fight infection

• platelets to help the blood clot

With MDS, the bone marrow doesn't make enough normal blood cells. The blood cells it does make are not fully developed and not able to work normally.

As the condition develops, the bone marrow may struggle to work properly. This may result in low numbers of normal blood cells in the bloodstream. The immature cells (blasts) in the bone marrow can also grow in number and spill out into the bloodstream.

The low number of blood cells and increased immature cells can eventually cause symptoms. The symptoms may be difficult to control.

Causes of MDS

We don't know what causes most cases of MDS. This is called primary MDS.

Although rare, MDS can be caused by radiotherapy or chemotherapy treatment for cancer. This is called secondary or treatment related MDS.

Anything that increases the risk of getting a disease is called a risk factor. Researchers have identified some risk factors that make the risk of developing MDS more likely. Having one or more of these risk factors doesn’t mean that you will definitely get MDS.

One risk factor is exposure to the chemical benzene. People are most likely to come into contact with benzene through work in certain industries. It is used in the rubber industry and is one of the chemicals in petrol. It is also in cigarette smoke.

A small number of people may develop MDS due to an inherited ​gene​ change (fault). Your doctor might do tests to look at gene changes. This is usually for:

• people who develop MDS at a young age

• families with MDS or people with a type of cancer called acute myeloid leukaemia (AML)

Signs and symptoms of MDS

Some people with a myelodysplastic syndrome do not have any symptoms at all. Their MDS is picked up on a routine blood test for something else.

For most people, symptoms tend to be mild at first and slowly get worse. The symptoms are caused by a drop in the number of blood cells and could include:

• tiredness and sometimes breathlessness because of a low level of red blood cells (anaemia)

• frequent infections because of low levels of white blood cells

• bleeding - such as nosebleeds or bruising easily because of a low level of platelets

• flat spots under the skin caused by bleeding (petechiae)

You might also have pain or discomfort in your tummy (abdomen) from an enlarged spleen.

Get more information on tests and treatment for MDS

Types of MDS

There are different types of myelodysplastic syndrome (MDS). The different types are based on certain changes in the blood cells, the bone marrow and genetic changes to the cells. 

Doctors in the UK use 2 classification systems to describe the types of MDS. They are: 

• The World Health Organisation (WHO) system (last updated in 2022)

• The International Consensus Classification (ICC)

They look at:

• how many immature cells (blasts) there are in the blood

• how many immature cells there are in the bone marrow

• how normal the blood cells look

• genetic changes in the cells

The systems are quite complicated. Your doctor or specialist nurse can explain what this means in your situation.

Risk groups for MDS

As well as the different types of MDS, doctors group MDS according to how the disease is most likely to develop.

In some, but not all, MDS may develop into a of type blood cancer called acute myeloid leukaemia (AML). Doctors call this transformation. Some types of MDS have a higher risk of transforming into AML than others.

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.

Go to information about acute myeloid leukaemia (AML)

International Prognostic Scoring System 

The systems for grouping MDS according to likely outcome are the:

• Revised International Prognostic Scoring System (IPSS-R) and

• Molecular International Prognostic Scoring System (IPSS-Molecular)

The risk groups below are from the IPSS-R system: 

• 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

Doctors also use the IPSS-molecular scoring system. It can provide more information to help them understand the risk of transformation to AML. 

Knowing what type of MDS you have, and your risk score helps your doctor to decide on the best treatment for you.

Read about the different treatments for MDS