What is AML?

Below we discuss how acute myeloid leukaemia (AML) starts, what causes it, who gets it, and more.

Overview

Acute leukaemia is a blood cancer that appears suddenly and grows quickly. It starts when undeveloped white blood cells – called blast cells – 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 undeveloped 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 also little room for normal red blood cells and platelets. This can cause fatigue, bleeding problems and other health issues.

There are 2 main types of acute leukaemia: acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL).

What is the difference between acute and chronic leukaemia?

While all types of leukaemia start in the bone marrow and affect how white blood cells are made, they are grouped according to the type of white blood cell 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 mature or partly developed cells, appears gradually and grows slowly over months to years.

For more on this see Chronic leukaemia (CLL) or Chronic leukaemia (CML).

What is the difference between AML and ALL?

The difference between AML and ALL is the type of white blood cell affected.

Acute myeloid leukaemia (AML) – Develops from myeloid cells. There are more than 20 subtypes of AML, including a subtype known as acute promyelocytic leukaemia (APML) that develops from immature myeloid cells called promyelocytes. APML is treated differently.

See more on AML risk factors and symptoms and read more on how AML is diagnosed and treated.

Acute lymphoblastic leukaemia (ALL) – ALL can develop from different types of lymphocytes, including B-cells or T-cells.

T-cell ALL is very similar to T-cell lymphoblastic lymphoma, and the 2 conditions are often treated the same way. In T-cell ALL, the abnormal lymphocytes are mainly in the blood and bone marrow, while in T-cell lymphoblastic lymphoma, the abnormal lymphocytes are in the lymph nodes.

See more on ALL risk factors and symptoms and read more on how ALL is diagnosed and treated.

Some people have a type of leukaemia called mixed-phenotype acute leukaemia (MPAL). This means the disease has features of both ALL and AML. MPAL may also be called biphenotypic acute leukaemia.

How leukaemia starts

The bone marrow produces 3 main types of blood cells: white cells, red cells and platelets. Leukaemia starts when abnormal white blood cells crowd the bone marrow and are pushed out into the bloodstream. Without treatment, they can spread to lymph nodes and some organs.

What causes AML?

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 and/or obesity
• particular blood disorders, such as myelodysplasia (for AML)
• some viruses, such as Epstein-Barr virus, but this is rare.

Who gets AML?

About 5200 people are diagnosed with a form of leukaemia in Australia each year. About 1500 of these cases are acute leukaemia.

AML is the most common type of acute leukaemia in adults, with about 1100 people diagnosed each year. It becomes more common with age and mostly occurs after 60.

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 bones.

Bone marrow contains blood stem cells. These are unspecialised cells that usually grow into one of the 3 main types of blood cells: white blood cells, red blood cells or platelets. Each type of blood cell has a specific job to do.

	White blood cells – fight infection.
	Red blood cells – carry oxygen around the body.
	Platelets – help the blood clot.

There are 2 families of blood stem cells: lymphoid and myeloid. These develop into different types of white blood cells that can be affected by different types of leukaemia.

When myeloid stem cells grow abnormally, this is called acute myeloid leukaemia (AML); when lymphoid stem cells grow abnormally, this is called acute lymphoblastic leukaemia (ALL).

Blood stem cell families

Stem cells divide into 2 families (lymphoid or myeloid), then become immature cells (lymphoblast or myeloblast cells). If cells are normal, they develop into different kinds of mature cells.

→ READ MORE: AML symptoms