Blood is pumped around the body by the heart. It supplies food, oxygen, hormones and other chemicals to all the body's cells. It also helps to remove waste products and fight infection.
Blood is made of a clear liquid called plasma and three types of cells:
- red blood cells, which collect oxygen from your lungs and carry it to all parts of your body. If you don't have enough red blood cells you have anaemia. Anaemia can make you look pale, may cause headaches and make you feel tired, dizzy and irritable.
- platelets, which are needed to help your blood to clot following an injury. Too few platelets may cause lasting bleeding or easy bruising.
- white blood cells, which play a major role in the body's defence against infection. Too few white blood cells puts you at risk of infection.
All blood cells come from the same type of cell, known as stem cells. Early on, they develop into either myeloid or lymphoid cells.
- Myeloid cells include all red blood cells, platelets and the white blood cells that are known as granulocytes and monocytes.
- Lymphoid cells include all other white blood cells, known as lymphocytes.
Blood cells are made in bone marrow, the spongy part in the centre of your bones. When the body is healthy, the numbers of red cells, white cells and platelets in the blood are kept in balance. Diseases of the blood cells, like leukaemia, can cause this balance to be thrown out.
Leukaemia is cancer of blood-forming cells. Leukaemia usually causes large numbers of white blood cells to be made.
These abnormal cells usually can't carry out the normal functions of white blood cells. They crowd the bone marrow and spill into the blood and may then spread into organs such as the liver, spleen, lungs and kidneys. Sometimes, they may also spread into the fluid around the brain and spinal cord.
Because there are so many abnormal white cells crowded into the bone marrow, the marrow sometimes can't make enough normal red blood cells, white blood cells and platelets.
Types of leukaemia
There are several types of Leukaemia. Some types appear suddenly and progress rapidly over days to weeks. Others are less apparent and progress slowly over months to years. In general, but not always, acute leukaemias develop more rapidly and chronic leukaemias develop more slowly.
Leukaemias are named according to the type of blood cells involved. The myeloid leukaemias are those which involve the granulocytes, red blood cells, platelets and monocytes; the lymphocytic leukaemias are those which involve the lymphocytes.
Acute lymphocytic leukaemia (ALL)
Acute lymphocytic leukaemia is most common in children. Some adults also develop this type of leukaemia.
Normal lymphocytes fight infection: when the body is attacked by bacteria or viruses, lymphocytes respond by producing antibodies or special killer cells. When you have acute lymphocytic leukaemia, the lymphocytes can't function properly, and you may develop a serious infection. The disease also causes many abnormal lymphocytes to be produced, crowding out the normal red blood cells and platelets.
This is sometimes called ‘lymphoblastic' leukaemia.
Chronic lymphocytic leukaemia (CLL)
This leukaemia also affects the lymphocytes, but usually develops much more slowly than acute lymphocytic leukaemia.
This disease affects adults and doesn't occur in children.
The disease progresses slowly, so the normal cells aren't crowded out as rapidly as in the acute type of the disease. If you have chronic lymphocytic leukaemia, you may not feel any symptoms until the later stages of the disease. In some cases, symptoms never occur because the disease progresses so slowly.
There are some very rare forms of chronic lymphocytic leukaemia called prolymphocytic leukaemia and hairy cell leukaemia. In addition, there's a form of non-Hodgkin lymphoma which, when it affects the blood, can mimic chronic lymphocytic leukaemia and is called mantle cell lymphoma.
Acute myeloid leukaemia (AML)
This leukaemia mainly affects adults, but can occur in children and adolescents.
Acute myeloid leukaemia mainly affects the myeloid cells known as granulocytes, but also red blood cells, platelets and monocytes. The disease creates too many young myeloid cells and not enough mature myeloid cells. The young myeloid cells can block blood vessels.
Cancer care pathways
For an overview of what to expect during all stages of your cancer care, read or download the What To Expect guide for acute myeloid leukaemia (also available in Arabic, Chinese, Greek, Hindi, Italian, Tagalog and Vietnamese – see details on the site).
Chronic myeloid leukaemia (CML)
Chronic myeloid leukaemia can occur at any age, but is uncommon below the age of 20 years.
Too many myeloid cells are present. Chronic myeloid leukaemia occurs in two stages: first, there's a slow multiplication of abnormal cells. Then, it can quickly change into an acute stage.
Causes of leukaemia
The causes of leukaemia aren't known. Some risk factors appear to influence its development. These risk factors only explain a very small number of leukaemia cases. Having one or more of these factors doesn't mean that you'll definitely develop leukaemia. Talk to your doctor if you're concerned about any of these factors.
Genetic factors: Down syndrome children and children born with some other rare gene changes have an increased risk of acute leukaemia. Genetic factors may play a role in chronic lymphocytic leukaemia – it's more common in men and seems to run in families.
Radiation: leukaemia occurs at higher than average rates among people exposed to intense radiation. These include survivors of atomic bomb explosions in Japan, people exposed to radiation after the Chernobyl nuclear plant disaster, and people who received large amounts of radiation for treatment of some medical conditions in the past. No leukaemia has been linked to radiation from x-rays and CT scans.
Chemicals: workers exposed to benzene have an increased risk of acute myeloid leukaemia. Smoking appears to increase the risk of acute myeloid leukaemia.
Country of origin: in certain areas of the world, such as south-west Japan, parts of Africa and the Caribbean, a particular type of leukaemia can be spread among local residents by a virus known as HTLV (human T-cell leukaemia / lymphoma virus).
How common is leukaemia?
In Victoria, over 790 people are diagnosed with leukaemia each year.
Expert content reviewers:
Annie Angle cancer nurse, Diploma Oncology Nursing, Royal Marsden, London