Normally, the spongy tissue found inside bones (bone marrow) produces:
But in MDS, your bone marrow doesn't make enough of these healthy blood cells. Instead, it makes abnormal cells that aren't fully developed (immature).
As the condition develops, your bone marrow gets gradually taken over by the immature blood cells, which don't work properly.
They squeeze out the healthy ones, making the number of cells that manage to get into the bloodstream lower and lower.
The condition can develop slowly (indolent) or quickly (aggressive), and in some people it can develop into a type of leukaemia called acute myeloid leukaemia (AML).
MDS can affect just one type of blood cell or many, depending on the type of disease you have.
Until 2016, the types of MDS were called:
In 2016, the World Health Organization (WHO) changed the terms to:
There are other types of MDS, and your doctor may also talk to you about the "risk group" of your MDS. This refers to how likely it is that your MDS might develop into AML.
Find more information on the types and risk groups of MDS:
The symptoms you have will depend on the type of MDS. For most people, symptoms are mild at first and slowly get worse.
They can include:
Some people with MDS don't have any symptoms and it's only picked up after they have blood tests for something else.
If you have any of these symptoms, you should speak to your GP about them.
Some people with MDS go on to develop acute myeloid leukaemia (AML), which is cancer of the white blood cells.
This is known as "transformation". It can take a few months or up to several years before transformation takes place.
The risk of this happening depends on what kind of MDS you have, and the number of normal and abnormal blood cells you have.
Ask your doctor about your risk of developing AML.
The type of treatment you get will depend on the type of MDS you have, your risk of developing AML, and whether you have any other health conditions.
The aim of treatment is to get the number and type of blood cells in your bloodstream back to normal and manage your symptoms.
If your MDS has only a low risk of transforming into cancer, you may not need any treatment at first and may just be monitored with regular blood tests.
Symptoms of MDS can often be controlled with a combination of the following treatments:
The medicine lenalidomide can be used to treat a rare type of MDS called deletion 5q, or del(5q).
People with del(5q) can have severe anaemia (a lack of red blood cells), which requires regular blood transfusions.
Lenalidomide is a type of treatment called a biological therapy. It's swallowed as a capsule and affects the way your immune system works.
Azacitidine is type of drug called a hypomethylating agent, which is injected under the skin.
It may be offered to people with more serious types of MDS, and may improve blood production and slow down the progress of MDS.
Chemotherapy is sometimes given if you have a type of MDS that increases your risk of AML.
It involves taking drugs that destroy the immature blood cells by stopping them growing. The drugs are taken either as a tablet or an injection.
Your chemotherapy treatment will probably be similar to that used for AML. Read about how AML is treated.
A stem cell transplant (also called a bone marrow transplant) is given after chemotherapy.
It involves replacing your abnormal blood cells with healthy cells from a donor. These healthy blood cells are fed into your bloodstream via a drip.
It can sometimes cure MDS, but isn't suitable for everyone.
A stem cell transplant will generally only be offered if you're young and otherwise in reasonably good health, as it's a very intensive treatment.
It helps if you have a suitable donor in your family (a close relative, such as a brother or sister), but in some cases it's possible to have a stem cell transplant using an unrelated donor whose tissue type closely matches yours.
Read more about having a stem cell transplant.
In most cases, the cause of MDS is not known. This is called primary MDS.
In rare cases, MDS can be caused by chemotherapy. This is known as secondary MDS, or treatment-related MDS.
MDS doesn't normally run in families, but some rare types occasionally do.
MDS is diagnosed by carrying out blood tests and bone marrow tests.
The blood tests will show how many normal and abnormal blood cells you have.
A bone marrow test involves taking a sample of your bone marrow, usually from your hip bone, under local anaesthetic.
The doctor passes a needle through your skin and into your bone, drawing out a sample of your bone marrow into a syringe. This will be sent to a laboratory to be examined under a microscope.
The bone marrow test takes 15 to 20 minutes and can be done on the ward or in the outpatients department.
Visit Cancer Research UK for more information about the bone marrow test.
Having MDS may have a significant impact on your life, both emotionally and physically.
There are organisations that offer support and information to people diagnosed and living with MDS, including:
The treatment of MDS is constantly evolving and new drugs are being tested all the time.
You may be offered the chance to enter a clinical trial.
Find out more about: