Leukaemias are cancers of the cells in the bone marrow that produce the various types of white blood cell in the blood. When a person has leukaemia there is a large increase in the number of cells of a particular type in the bone marrow or in the blood. These cells do not function normally and provide no protection against infection. The other components of the bone marrow (red blood cells, platelets and normal white blood cells) get crowded out and are reduced in number. Different types of leukaemia affect different age groups. Exposure to radiation can cause some types.
The most common type in young children kills 90% of affected children within 6 months. However, in territories where treatment is now available, most children who are given treatment will improve for a time and over half are cured. Treatments are not as successful in adults.
Leukaemia caused 0.5% of all deaths worldwide in 2002, an average of 42 deaths per million people per year and 4% of all deaths from cancer.