Leukemias are cancers of the blood and occur when there is an excess accumulation of abnormal (immature) blood cells (called blasts). Instead of maturing normally, large numbers of these blast cells turn into abnormal white blood cells. These abnormal cells cannot 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, kidneys and into the cerebro spinal fluid to the brain.
In leukemia, the cells do not mature properly but continue to multiply and the bone marrow is replaced by these abnormal cells spilling over into the blood. Because the bone marrow can no longer produce sufficient normal blood cells and platelets, anemia, infections and bruising occurs.
Leukemia occurs in several forms. Some forms appear suddenly and progress rapidly over days to weeks. These are called acute leukemias. Others are less apparent and progress slowly over months to years. These are the chronic leukemias. Leukemia are also described according to the type of white blood cell which is involved; granulocytes (formed from immature cells called myeloblasts) or lymphocytes. The four main types of leukemia are:
- Acute Lymphoid Leukaemia (ALL) - generally occurs in young children, but can occur in adults.
- Acute Myeloid Leukaemia (AML) - usually occurs in adults, but can occur in children.
- Chronic Myeloid Leukaemia (CML) - can occur at any age, but is uncommon below the age of 20 years.
- Chronic Lymphoid Leukaemia (CLL) - usually occurs in older people and is rare under the age of 35 years.
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