Children's cancer
JMML used to be called:
juvenile chronic myelogenous leukaemia (JCML)
chronic myelomonocytic leukaemia of childhood
Leukaemia means a cancer of the blood forming system. The blood forming system is the bone marrow, the soft inner part of your bones. Although JMML has leukaemia as part of its name, the World Health Organisation (WHO) does not classify it as a leukaemia. It's now included in a group of blood cancers called myeloproliferative and myelodysplastic disorders.
Bone marrow is a spongy material that fills the bones.
It contains early blood cells, called stem cells. These develop into the 3 different types of blood cells.
Normally stem cells in your bone marrow keep dividing to make new blood cells. This keeps the numbers of cells circulating in your blood within a normal range.
Doctors can measure the number of blood cells your child has from a blood test. They call this their blood count.
A myeloproliferative disorder is a condition where there are too many blood cells made. A myelodysplastic disorder is where the blood cells made are abnormal and not fully mature. In reality, the two disorders often overlap, which is why the WHO has put them together in the same category here.
In JMML it is a specific type of white blood cells called monocytes that are abnormal. Monocytes are part of the immune system and help the body to fight infection. Too many are produced, and they are not developed enough to work properly. It is also more difficult for the bone marrow to produce other blood cells such as:
red blood cells
platelets
other white blood cells
This is because the monocytes take up a lot of space in the bone marrow.
The abnormal white blood cells are made in the bone marrow, enter the bloodstream and circulate around the body. They don't work normally, so children with JMML don't have the same protection against infection as they should.
This means your child might have a lot of infections. Or find it more difficult to recover from infections they do have.
Children of any age can be diagnosed with JMML. Over half of those diagnosed (over 50%) are under 2 years old. It’s slightly more common in boys than girls. But we don’t know why.
We don’t know what causes, or how to prevent, JMML. It’s not something you or anyone has done, and no one is to blame.
Children with a genetic disorder called are more at risk of developing JMML. But this only happens in between 10 to 15 out of every 100 cases (between 10 to 15%).
Some of the symptoms of JMML are similar to those of other childhood illnesses. And they vary between children. Remember JMML is rare. And it develops fairly slowly. This means that symptoms might develop over weeks or months.
In JMML, as the abnormal blood cells multiply in the bone marrow, fewer normal blood cells are made. If there are not enough normal blood cells, the body cannot work normally.
Because of this, there are a number of symptoms in children with JMML. Your child might have a combination of these. Symptoms include:
being tired, lethargic and generally feeling unwell
being irritable – it might take a young child longer to settle
bruising easily
nosebleeds and bleeding gums
looking pale
fever
getting lots of infections
an enlarged liver and – you might have noticed your child has jumped a nappy or trouser size quickly
pain in the tummy – if the monocytes have collected in this area
skin rashes
cough and wheezing
Your child will need a number of tests if their doctor suspects they have JMML. Your child might have more than one test on the same day. And they only have the tests their team think are needed.
These tests aren’t generally painful. But, your child will have to keep still for some of them.
The main tests doctors use to diagnose JMML are:
Your child might also have other tests to see if any organs of the body are affected by the JMML. And to see how well they are generally.
These other tests might include:
x-rays
CT scans
MRI scans
spinal fluid test (lumbar puncture)
Finding out that your child has a rare condition like JMML can be devastating. Even if you have been told that it is a possibility, hearing this confirmed by a doctor can be shocking. You might feel numb and that it isn’t real.
There are a range of emotions you might feel including anger, disbelief and sadness. Sometimes a diagnosis can feel like a relief, especially if your child has been unwell for some time and you have been worrying about what’s wrong.
We have information written for parents of newly diagnosed children.
My child has just been diagnosed
More than 95 in 100 children with JMML (more than 95%) have changes in particular .
These include:
KRAS
NRAS
RRAS
CBL - children with CBL changes also often have poor growth, developmental delay and inflammation of the blood vessels
NF1 (neurofibromatosis type 1) - some children with NF1 gene changes have learning problems and are at increased risk of tumours that are cancerous or non cancerous (benign)
PTPN 11 - this is related to a genetic syndrome called Noonan syndrome
Doctors test for these gene changes as it helps decide which treatment is best. And researchers hope that learning more about JMML will improve treatment for all children with JMML in the future.
A small number of children with changes in the CBL gene do not need treatment straightaway. This is because there is a chance the JMML will go away without treatment. Your child will be followed up closely by their specialist team. This is called watch and wait.
Some children with the NRAS gene change might also be followed closely without treatment. This is because there is a chance the JMML will go away without treatment. Or they might have low dose chemotherapy. This is because their JMML might not require intensive treatment.
The treatment for all other children with JMML is a stem cell or bone marrow transplant. Some children need chemotherapy before this treatment. This is to get the JMML under control enough for transplant. They will then have more intensive chemotherapy as part of the transplant process.
A transplant involves having intensive cancer drug treatment, which has a good chance of destroying the immature white blood cells. But it also destroys the healthy stem cells in the bone marrow. The child then has a drip of new stem cells into their bloodstream after their high dose treatment. These are most commonly from:
family member, most often a brother or sister or
a donor from the transplant register
Tissue typing is a set of blood tests that show how closely a possible bone marrow donor’s tissue matches the person needing a transplant. The results help doctors decide who could be a possible donor. A brother or sister is most likely to be a match.
At the moment, this is the only type of treatment that can possibly cure JMML.
We have information about having a stem cell transplant. This information is written for adults with cancer, but you might find some of it useful.
Find out about having a stem cell transplant
We have some information about supporting your other children. It includes tips from parents. It includes some information about sibling donors for a stem cell or bone marrow transplant on the page.
Supporting brothers or sisters
Unfortunately, a transplant is only suitable for some children. Doctors and scientists are trying to improve treatment for this disease, but currently it is still difficult to cure.
Coping with your child’s diagnosis of JMML can be difficult, both practically and emotionally. Being well informed about your child's condition and their treatment can make it easier to make decisions and cope with what happens.
You might find some of our information on childhood cancer useful to read. There is a list of support organisations, including those who provide support and information for families with children with any serious illness.
For support and information, you can call the Cancer Research UK information nurses on freephone 0808 800 4040, from 9am to 5pm, Monday to Friday. They can give advice about who can help you and what kind of support is available.
Leukaemia Care provide support to anyone affected by blood cancer. They have information on their website about JMML.
Visit the Leukaemia Care website to see the JMML information
Last reviewed: 12 Dec 2023
Next review due: 12 Dec 2026
Find out about other conditions that can be confused with cancer or can develop into a cancer. We also have information about less common blood cancers here.
Get information about the possible symptoms of cancer and when to see a cancer specialist.
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