What is acute lymphoblastic leukaemia (ALL)?

How does the body make blood cells?

To understand how and why leukaemia affects you as it does, it helps to know how you make blood cells.

Your body makes blood cells in the bone marrow. You need to make a continuous supply of blood cells to keep your body healthy and functioning properly.

All blood cells start as the same type of cell, called a stem cell. This stem cell then develops into:

• lymphoid stem cells

• myeloid stem cells

Lymphoid stem cells

Lymphoid stem cells develop into white blood cells called lymphocytes. Examples of lymphocytes include B lymphocytes and T lymphocytes.

Myeloid stem cells

Myeloid stem cells can become:

• monocytes

• red blood cells

• platelets

• white blood cells called granulocytes. Neutrophils are one type of granulocyte

The diagram below helps to explain this:

Read more about the blood and circulation

What happens in ALL?

In acute lymphoblastic leukaemia, the bone marrow makes too many B or T lymphocytes. These lymphocytes are not fully developed and are not able to work normally. They are often known as blast cells. They grow and divide quickly.

These abnormal cells build up in the bone marrow and stop healthy blood cells from developing. They also spill out into the blood and can spread into other parts of the body. This includes the:

• ​lymph nodes​

• liver

• ​spleen​

• brain and ​spinal cord​

• testicles, although this is rare

The word acute means that the leukaemia can develop quickly. This is different from chronic leukaemia which usually develops very slowly. There are several different types of leukaemia.

Find out about other types of leukaemia

People with ALL usually need to start treatment quite quickly after being diagnosed. Treatments can work well for some people with ALL but survival depends on many factors.

Read more about survival for ALL

Types of acute lymphoblastic leukaemia (ALL)

Acute lymphoblastic leukaemia has various types and subgroups. Doctors work this out by looking at the structure and features of the leukaemia cells. And if it affects the B or T lymphocytes. Knowing the type helps your doctor decide which treatment you need.

The types of ALL include:

B cell acute lymphoblastic leukaemia (B cell ALL)

This is the most common type of ALL in adults. It affects the B cell lymphocytes. Around 75 out of every 100 people with ALL (around 75%) are this type.

B cell ALL can be further divided into subgroups, the most common subgroup is precursor B cell ALL. Your doctor may talk to you about this.

T cell acute lymphoblastic leukaemia (T cell ALL)

It might also be called pre (precursor) T cell ALL. This is more likely to affect young adults and is more common in men. Around 25 out of every 100 people with ALL (around 25%) are this type.

Your doctor might discuss what subtype of T cell ALL you have.

Philadelphia positive ALL

Philadelphia positive leukaemia is when you have a particular change in the ​chromosome​ of the leukaemia cells. 

Philadelphia positive ALL happens when a ​gene​ called the ABL1 on chromosome 9 breaks off and sticks to a gene called the BCR on chromosome 22. It produces a new gene called BCR-ABL1 which causes the cell to make too much of a protein called tyrosine kinase. This protein encourages leukaemia cells to grow and multiply.

Philadelphia positive ALL is more common in older people. Researchers believe that between 20 and 30 out of every 100 people with ALL (between 20 and 30%) are Philadelphia positive. Doctors treat Philadelphia positive ALL with a targeted cancer drug called imatinib.

Watch this 2 minute video to explain what Philadelphia positive leukaemia is.

How leukaemia can affect you

Leukaemia can affect your blood and other areas of your body.

White blood cells

White blood cells help fight infection. If your body makes a lot of abnormal white blood cells, they can prevent normal healthy cells from developing. So you are more likely to get infections and may find it difficult to get rid of them.

Red blood cells and platelets

Too many white blood cells can overcrowd the bone marrow. So there isn't enough space to make other types of blood cells. This can cause a lower than normal number of red blood cells and platelets.

Having too few red blood cells is called anaemia.  It can cause you to feel tired and breathless.

Platelets are blood cells that help the blood to clot. If you don’t have enough platelets you can have bleeding problems such as nosebleeds and bruising.

Other parts of your body

Abnormal white blood cells can build up in parts of your body such as the spleen, lymph nodes and liver making them bigger.

This can make your tummy (abdomen) swell and feel uncomfortable. The leukaemia cells can also spread to the brain. In men the testicles are sometimes affected, so let your doctor know if you have any swelling or pain in that area.

Unlike solid tumours, for example breast cancer, having leukaemia cells in different parts of your body doesn’t mean a worse outcome.

Read more about the symptoms of ALL

How common is ALL?

Acute lymphoblastic leukaemia is rare. Around 760 people are diagnosed with ALL in the UK each year. This number includes children and adults diagnosed with ALL.

Who can get ALL?

ALL is most often diagnosed in children. It is most common in young children aged 0 - 4 years. It is slightly more common in males than in females. 

Find out about risks and causes of ALL