Acute lymphoblastic leukaemia (ALL) is a type of blood cancer. Itstarts from white blood cells called lymphocytes in the bone marrow. The bone marrow is the soft inner part of the bones, where new blood cells 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.
How common is ALL?
Acute lymphoblastic leukaemia is rare. Around 790 people are diagnosedwithALL in the UK each year.
ALL is most often diagnosed in children.It is most common inyoung children aged0 - 4 years. It is slightly more common in males than in females.
- Find out about risks and causes of ALL
What happens in ALL?
The wordacutemeans that the leukaemia can developquickly. This is because the lymphocytes are growing and dividing much quicker than usual.These abnormal cells build up in the bone marrow and spill out into the blood.
The leukaemiacells canspread into other parts of the body, including the:
lymph nodes 
- liver
spleen - central nervous system (brain and spinal cord)
- testicl*s
The leukaemia cells can build up in the lymph nodes, liver and spleen and sometimes make them bigger.
If it wasn't treated acute leukaemia would cause death within a few weeks or months. But treatments can workwell for somepeople with ALL.
Blood cells and ALL
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. The bone marrow is the soft inner part of your bones. You make blood cells in a controlled way, as your body needs them.
All blood cells start as the same type of cell, called a stem cell. This stem cell then develops into:
- lymphoid stem cells, which become white blood cells called lymphocytes
- myeloid stem cells, which become white blood cells called monocytes and neutrophils (granulocytes), red blood cells and platelets
The diagram helps explain this:
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.
- Read more about the blood
Types of leukaemia
There are several types and subtypes of leukaemia. The name of the leukaemia you have depends on:
- how quickly it develops
- the type of white blood cells it affects
Doctors divide leukaemia into two main groups, acute and chronic. Acute leukaemia develops very quickly. Chronic leukaemia tends to develop slowly. Usually over months or years without causing many symptoms.Doctors divide these groups further depending on the type of white blood cell they affect.
In acute leukaemia:
- acute myeloid leukaemia (AML) affects myeloid cells
- acute lymphoblastic leukaemia (ALL) affects lymphoid cells
In chronic leukaemia:
- chronic myeloid leukaemia (CML) affects myeloid cells
- chronic lymphocytic leukaemia (CLL) affects lymphoid cells
- Find out about other types of leukaemia
Types of acute lymphoblastic leukaemia
Acute lymphoblastic leukaemia has various types and subgroups.Doctors work this out by looking at the structure and features (characteristics) of the leukaemia cells.And if it affects the B or T lymphocytes.Knowing this information helps your doctor decide which treatment you need.
The types and subgroups 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. B cell ALL can be further divided into subgroups, including:
- precursor B cell ALL
- mature B cell ALL (this is sometimes called Burkitt type ALL)
- Common ALL
- Pro B cell ALL
Precursor B cell ALL is the most common subtype of ALL in adults. Around 75 out of every 100 people with ALL (around 75%) are this type.
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. Around25 out of every 100 people with ALL (around 25%) are this type.
Philadelphia positive ALL
About 20 to 30out of every 100 people with ALL (about 20 to30%) have this type of ALL. In Philadelphia positive leukaemia you have a particular change in the 
of the leukaemia cells.
Philadelphia positive ALL happens when a calledthe 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 thecell to make too much of a protein called tyrosine kinase. This protein encourages leukaemia cells to grow and multiply.
Doctors treat Philadelphia positive ALL with a targetedcancer drug, this is usually imatinib, which blocks this protein.
Watch this 2 minute video to explain what Philadelphia positive leukaemia is.
Transcript
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. Sectionsof DNA are called genes.They carry the information that makes you you. Forexample, they tell your body what colour your hairwill 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 makeexact copies of the chromosomes.
In Philadelphia chromosome positive leukaemia anabnormal change happens to chromosomes 9 and 22.Part of chromosome 9 breaks off where the gene ABL1is located and part of chromosome 22 breaks offwhere the BCR gene is located. The broken partsswap 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 whichencourages leukaemia cells to grow.
There are targeted cancer drugs that can block theprotein and stop the leukaemia from growing. Thesedrugs are called tyrosine kinase blockers. You takethem as tablets.
For more information about your type of leukaemiaand treatments go to CRUK.org/about-cancer/leukaemia.
How leukaemia can affect you
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.
Too many white blood cells can overcrowd the bone marrow. Sothere isn't enough space to make other types of blood cells. This can causea lower than normal number of red blood cells and platelets.
Having too few red blood cells (called anaemia) makes you tired and breathless. You can have bleeding problems such as nosebleeds, if you don’t have enough platelets.
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 testicl*s 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 about the symptoms of ALL
