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What is CML?
CML (chronic myeloid leukaemia) is a leukaemia that grows slowly and causes too many white blood cells to form. Normal blood cells grow and divide to form new blood cells as the body needs them. When normal cells grow old or get damaged, they die. CML cells don't do this. Instead, they make new cells that aren't needed and don't die quickly when old or damaged.
How does CML develop?
Genes are the coded instructions in cells for making new cells and controlling how cells behave. Sometimes parts of chromosomes beak off and switch with each other. This 'event' is called a translocation. CML is caused by such an event where the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9 swop parts, each one with the other. The result is a new fusion gene called BCR-ABL1. This abnormal gene is located on the new shortened chromosome 22 and is called the Philadelphia chromosome.
CML has three phases
The first or chronic stage of CML is characterised by marked increases in the numbers of normal-appearing white blood cells and sometimes platelets. During the course of the disease, more and more leukaemia cells fill the bone marrow and enter the bloodstream.
Eventually the leukaemia cells undergo more changes, and the disease progresses to an accelerated phase and then inevitably to the end stage of the disease, called the blast phase. In the blast phase, only very immature leukaemia cells populate the marrow and blood, a sign that the disease has become much worse. Massive enlargement of the spleen is common in the blast phase, as well as fever and weight loss.
- Chronic phase: An initial period that may last months to years during which the disease progresses very slowly
- Accelerated phase: The disease begins to progress more quickly, treatments are less effective, and symptoms worsen
- Blast phase: Immature leukaemia cells (blasts) appear and the disease becomes much worse, with complications such as serious infections and excessive bleeding
Who gets Chronic Myeloid Leukaemia?
Chronic myeloid leukaemia (CML) may affect people of any age and of either sex but is uncommon in children younger than 10 years. The disease most commonly develops in adults between the ages of 40 and 60. In approximately 95% of cases, there is a rearrangement of particular parts of chromosome 9 with 22 which results in a new abnormal chromosome 22 named as the Philadelphia chromosome. The Philadelphia chromosome produces an abnormal enzyme (a tyrosine kinase), which is responsible for the abnormal growth pattern of the Ph+ white blood cells in CML.