What is acute lymphoblastic leukaemia (ALL)?

Updated 10 Aug 2017

Acute lymphoblastic leukaemia (ALL) is an acute form of leukaemia or cancer of the white blood cells that affects blood-producing cells in the bone marrow. It happens when these cells don’t mature properly, and grow too fast. In this section you can find out more about how your body works and how ALL develops.

What is acute lymphoblastic leukaemia (ALL)?

ALL affects cells called lymphoblasts (or blast cells, for short). They’re a type of white blood cell, which are a vital part of your immune system. Lymphoblasts are the immature cells that should develop into lymphocytes, in your bone marrow.

Your body needs new lymphocytes all the time, and it usually makes the right amount. When people have ALL this process goes wrong. The blast cells reproduce too quickly, and they don’t mature properly. We’ll refer to these immature blast cells as leukaemia cells.

The leukaemia cells build up in your bone marrow and eventually there’s no room for normal blood cells to be made there. So your body doesn’t have enough white blood cells, red blood cells, or platelets to work properly.

These cells can eventually spread to other parts of the body, including the liver, lymph nodes, spleen and the central nervous system. There are other types of cancer that can originate in these organs and then spread to the bone marrow. However, these cancers are not leukaemia.

ALL develops more quickly than some other blood cancers, so quick diagnosis and treatment are really important.

Types of ALL

There are different subtypes of ALL. The treatment you’ll have may differ depending on which specific type you’re diagnosed with. There are different types of lymphocytes, known as B cells and T cells. When you have ALL, it usually affects one type or the other, so doctors will say you have either:

  • B-cell ALL (this is the most common type)
  • T-cell ALL (more common in young people and men)

Philadelphia positive ALL

There’s a third type of ALL called Philadelphia positive ALL, which around one in four people with ALL have.

This is where the leukaemia cells divide more often and live longer than usual because of a very specific fault. To explain this fault we’ll give a very brief explanation of chromosomes.

All cells in your body contain a set of ‘instructions’ which tell the cell what to do and when to do it. These instructions are stored inside the cells in structures called chromosomes. The chromosomes are made up of a chemical known as DNA. The DNA is arranged in sections called genes. There are 23 pairs of chromosomes in each cell in your body. When cells divide to form new cells, normally the chromosomes stay the same in each new cell.

This type of ALL is thought to begin when an event takes place which doesn’t usually happen. A small part (the ABL1 gene) of chromosome 9 gets stuck next to a small part (the BCR gene) of chromosome 22 by mistake when the cell divides. They form a new fusion gene called BCR-ABL1 and make chromosome 22 shorter than normal. This new, shorter chromosome is called the Philadelphia chromosome, because that’s where it was discovered.

This swapping of genetic material is called a translocation, or chromosomal translocation. This particular translocation is sometimes called t(9;22).

The new BCR-ABL1 gene is important in the development of Philadelphia positive ALL because it makes a new protein (also called BCR-ABL1). This protein is a type of enzyme known as tyrosine kinase, which causes the leukaemia stem cells to divide more often and to live longer than usual.

If doctors can detect the BCR-ABL1 fusion gene, it can help them to diagnose ALL – and also monitor your response to treatment. The standard treatment for Philadelphia positive ALL is drugs that inhibit the tyrosine kinase enzyme and block its effects.

Other subtypes of ALL

There are numerous other genetic subtypes of ALL. Some of them are known to be related to better or worse outlooks, although, at present, there are no specific therapies for these subtypes and they are all treated in the same way. This is a very active area of research for scientists internationally.

What causes ALL?

Around 650 people are diagnosed with ALL in the UK each year.

We don’t know exactly what causes ALL yet. What we do know is that it’s not possible to ‘catch’ ALL or any other type of leukaemia. Below are some factors that may affect a person’s chances of getting ALL.


ALL is the only type of leukaemia that happens more often in children than in adults. When ALL does happen in adults, it’s more likely to affect younger people. It’s less likely in middle age, and then starts to occur more often again in older people. We don’t know the reason for this pattern.


ALL is slightly more common in men than women. We don’t know why.

Family history

As far as we know, adult ALL doesn’t usually run in families. There are some rare cases where this can happen, but it doesn’t apply to most people.


Radiation in high doses can lead to leukaemia, but it’s unlikely to cause many cases in the UK, if any at all. It’s important to remember that none of your lifestyle choices have contributed to this condition.

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