Acute lymphoblastic leukaemia (ALL)

Acute lymphoblastic leukaemia (ALL) is a blood cancer that appears suddenly and grows quickly. It starts when immature white blood cells called blasts become cancerous. These abnormal blast cells are known as leukaemia cells. They multiply quickly and continue to divide but never mature into normal cells.

Because the leukaemia cells are immature and abnormal, they don’t carry out the usual infection-fighting role of white blood cells. They also crowd out normal white blood cells, which then can’t work properly. This increases the risk of infections. When the bone marrow fills with leukaemia cells, there is little room for normal red blood cells and platelets. This can cause fatigue, bleeding problems and other health issues.

Learn more about:

• The difference between acute and chronic leukaemia
• The difference between ALL and AML
• How leukaemia starts
• What causes ALL
• Who gets ALL
• The blood
• The lymphatic system

What is the difference between acute and chronic leukaemia?

While all types of leukaemia start in the bone marrow and affect white blood cell production, they are grouped according to which type of white blood cell is affected, whether there are abnormalities in the bone marrow, and how quickly the disease develops.

Acute leukaemia usually affects undeveloped cells, occurs suddenly and grows quickly. Chronic leukaemia usually affects partly developed cells, appears gradually and grows slowly over months to years. For more on this see Chronic leukaemia – CLL or Chronic leukaemia CML.

There are two types of acute leukaemia:

• acute lymphoblastic leukaemia (ALL)
• acute myeloid leukaemia (AML).

What is the difference between ALL and AML?

ALL and AML are the two main types of acute leukaemia. The difference between them is the type of white blood cell affected.

Acute lymphoblastic leukaemia (ALL) – ALL can develop from different types of lymphocytes, including B-cells or T-cells. See more on how ALL is diagnosed and treated.

Acute myeloid leukaemia (AML) – Develops from myeloid cells. There are different subtypes of AML, including a subtype known as acute promyelocytic leukaemia (APML) that develops from immature myeloid cells called promyelocytes. APML is treated differently.

How leukaemia starts

The bone marrow produces three main types of blood cells: white cells, red cells and platelets. Leukaemia starts when abnormal white blood cells become cancerous and crowd the bone marrow before moving into the bloodstream. Without treatment, they can spread to lymph nodes and some organs.

What causes ALL?

The exact causes of acute leukaemia are not yet understood. Things known to increase the chance of developing the disease include:

• previous treatment with chemotherapy or radiation therapy
• having certain genetic disorders, such as Down syndrome
• exposure to high levels of radiation (e.g. nuclear accident)
• exposure to some chemicals, such as benzene
• smoking
• obesity
• particular blood disorders, such as myelodysplasia (for AML)
• some viruses, such as Epstein-Barr virus (for ALL).

Who gets ALL?

The blood

Blood is pumped around your body to provide oxygen and nutrients to your tissues, and to remove waste products. It is made up of blood cells carried in a clear fluid called plasma.

All blood cells live for a limited time and need to be continually replaced. Most are made in the bone marrow, which is the spongy part in the centre of the bones.

Bone marrow contains blood stem cells. These are unspecialised cells that usually grow into one of the three main types of blood cells: red blood cells, white blood cells or platelets. Each type of blood cell has a specific job to do.

There are two families of blood stem cells:

• lymphoid stem cells – develop into white blood cells called lymphocytes, which are an important part of the immune system
• myeloid stem cells – develop into red blood cells, platelets, and all white cells apart from lymphocytes.

When lymphoid white blood cells grow abnormally this is called acute lymphoblastic leukaemia and when myeloid white blood cells grow abnormally this is called acute myeloid leukaemia.