What is acute lymphoblastic leukaemia (ALL) and how does it affect children?

Updated 11 Aug 2017

Acute lymphoblastic leukaemia (ALL) is a form of cancer that affects blood-producing cells in the bone marrow. It happens when these cells don’t mature properly, and grow too fast.

The word ‘acute’ means developing quickly, while ‘lymphoblastic’ refers to the type of white blood cell it affects.

When your child is healthy and everything’s working normally, the lymphoid blast cells in your child’s bone marrow mature into fully formed white blood cells called lymphocytes.

All kinds of cancers involve changes in genes in the affected cells. In a child with ALL, a change occurs that means these lymphoid blast cells don’t mature properly and become cancerous. These cancerous cells collect inside the bone marrow, which means there isn’t room for enough normal blood cells to be made. This is what causes most of the signs and symptoms of ALL.

> Find out more about childhood leukaemia

What causes childhood ALL?

One of the most common questions asked by parents is ‘Why did my child get leukaemia?’ Our researchers are working all the time to find out more about what causes ALL in children.

At the moment we don’t know what causes ALL, although changes which occur by chance in the genes of cells in the bone marrow happen in many patients. It’s not possible to ‘catch’ ALL or any other type of leukaemia.

You’re not alone: there are almost 300 children diagnosed with ALL each year in the UK. It’s the most common type of childhood cancer.

ALL can affect any child. There are a number of factors which you can’t control that can lead to ALL.


Boys are slightly more likely to develop ALL than girls; we don’t know why.


ALL can occur at any age in childhood.

Family history

ALL can’t be passed on from a parent to a child. Children with some genetic conditions (such as Down’s syndrome) have a higher risk of developing ALL than other children.


Radiation in high doses can lead to childhood leukaemia, but it’s unlikely to cause many cases in the UK, if any at all.

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