What is acute lymphoblastic leukaemia (ALL)?
Acute lymphoblastic leukaemia (ALL) is a type of blood cancer. It starts from 
called lymphocytes in the bone marrow. The bone marrow is the soft inner part of the bones, where new are made.
ALL usually develops quickly over days or weeks. It is the most common type of leukaemia to affect children but can also affect adults.
This section is about ALL in adults. We have separate information about childhood 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:
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lymphoid stem cells
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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:
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.
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.
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 of the leukaemia cells.
Philadelphia positive ALL happens when a 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.
The human body is made up of trillions of cells. Inside each cell is a nucleus and within the nucleus are the cell’s chromosomes. There are 23 pairs in total.
Chromosomes are made up of DNA, which gives the instructions that tell a cell what to do. Sections of DNA are called genes. They carry the information that makes you you. For example, they tell your body what colour your hair will be or what colour your eyes will be.
Genes also tell your cells when to divide and grow, and when to die.
When cells divide to make new cells, they make exact copies of the chromosomes.
In Philadelphia chromosome positive leukaemia an abnormal change happens to chromosomes 9 and 22. Part of chromosome 9 breaks off where the gene ABL1 is located and part of chromosome 22 breaks off where the BCR gene is located. The broken parts swap places creating a new gene on chromosome 22.
This new chromosome is called the Philadelphia chromosome and the new gene is called BCR-ABL1. This new gene tells the cell to make a large quantity of a protein called tyrosine kinase which encourages leukaemia cells to grow.
There are targeted cancer drugs that can block the protein and stop the leukaemia from growing. These drugs are called tyrosine kinase blockers. You take them as tablets.
For more information about your type of leukaemia and treatments go to CRUK.org/about-cancer/leukaemia.
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.
How common is ALL?
Acute lymphoblastic leukaemia is rare. Around 765 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.
