Leukaemia is the general name given to a group of cancers that develop in the bone marrow.
Leukaemia originates in developing blood cells that have undergone a malignant change. This means they multiply in an uncontrolled way and do not mature as they should. Because they have not matured properly, these cells are unable to function properly.
Most cases of leukaemia originate in developing white cells. In a small number of cases leukaemia develops in other blood-forming cells, for example, in developing red cells or developing platelets.
The terms myeloid and lymphocytic refer to the types of cells in which the leukaemia first started. Myeloid stem cells develop into red cells, white cells (neutrophils, eosinophils, basophils and monocytes) and platelets. Lymphoid stem cells develop into two other types of white cells called T-lymphocytes and B-lymphocytes.
There are several different types, and subtypes, of leukaemia. Leukaemia can be either myeloid or lymphocytic, and acute or chronic.
Acute leukaemia develops and progresses quickly and therefore needs to be treated as soon as it is diagnosed. Acute leukaemia affects very immature blood cells, preventing them from maturing properly.
In chronic leukaemia there is an accumulation of more mature but abnormal white blood cells. Chronic leukaemia progresses more slowly than acute leukaemia and may not require treatment for a long time after it is diagnosed.
There are four main types of leukaemia:
- acute myeloid leukaemia (AML)
- acute lymphoblastic leukaemia (ALL)
- chronic myeloid leukaemia (CML)
- chronic lymphocytic leukaemia (CLL).
Both adults and children can develop leukaemia but certain types are more common in different age groups. CML is very rare in children and CLL virtually never occurs in this age group. ALL is the most common leukaemia in children and AML occurs occasionally.