Leukaemia is a cancer of the white blood cells.
White blood cells help to fight infection. There are two different types of white blood cell lymphoid cells (lymphocytes) and myeloid cells. CML affects the myeloid cells.
Normally the white blood cells, which are produced in the bone marrow, repair and reproduce themselves in an orderly and controlled way. In leukaemia, however, the process gets out of control and the cells continue to divide but do not mature.
These immature dividing cells – known as blast cells – fill up the bone marrow and stop it making healthy blood cells. As the blast cells are immature, they cannot work properly. This puts the child at increased risk of infection. The overproduction of white blood cells also interferes with the production of healthy red blood cells and platelets, leading to symptoms of Leukaemia such as anaemia and bruising.
In contrast to acute leukaemias (such as acute myeloid leukaemia and acute lymphoblastic leukaemia), this happens very slowly in CML
There are three different stages in the development of chronic myeloid leukaemia:
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- Chronic phase. There may be no symptoms of leukaemia, but blast cells are present in the blood and bone marrow. This phase can last several years before undergoing transformation to the second, accelerated phase.
- Accelerated phase. An increased number of blast cells are found in the blood and marrow and there is evidence that the number of normal cells is decreasing. This phase lasts three to nine months.
- Blast phase. Also called a ‘blast crisis’. During the third and final phase, the disease resembles acute leukaemia. More than 30% of bone marrow and blood cells are blast cells. Without effective treatment (see below) the disease is usually fatal within three to six months of entering the blast phase.