Leukaemia is a type of cancer of the blood and bone marrow. It occurs when the bone marrow makes too many white blood cells (lymphocytes), which are part of the body’s immune system to fight infections. Leukaemia cells do not function properly as white blood cells, and they do not fight infections very well. They can also crowd the bone marrow, meaning less room for healthy blood cells.
Different types of leukaemia are named after the type of stem cells that are affected (either lymphoid stem cells or myeloid stem cells), and how quickly the abnormal cells grow:
- Acute lymphocytic leukaemia, also known as acute lymphoblastic leukaemia, affects lymphoid stem cells and grows quickly. It is the most common type of leukaemia in children, occurring mostly in younger children (aged 2–4 years).
- Acute myeloid leukaemia affects myeloid stem cells and grows quickly. It is also called acute myelogenous leukaemia, acute myeloblastic leukaemia, acute granulocytic leukaemia or acute nonlymphocytic leukaemia.
- Chronic lymphocytic leukaemia affects lymphoid stem cells and usually grows slowly. It is the most common type of leukaemia in adults and is rare in children.
- Chronic myeloid leukaemia affects myeloid stem cells and grows slowly. It is rare in children, but tends to occur more often in teenagers than in younger children.