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CML is a blood and bone marrow disease that develops slowly.
There are three possible phases of CML: chronic, accelerated and blast phases.
The phase is determined by the number of immature cells called blast cells in the blood and bone marrow and by the extent of your symptoms. Most people are diagnosed when CML is in the chronic phase.
In this phase the CML develops very slowly and is often stable for a long time. It’s sometimes called the ‘stable phase’. There may be no symptoms and most people lead a normal life.
People in this phase rarely need to go into hospital. You can have treatment – which doesn’t usually cause many side effects – as an outpatient. You’ll have regular blood tests to check how well you’re responding to treatment.
Most people who start treatment in the chronic phase have their leukaemia well-controlled without any symptoms.
And, if they keep taking their treatment, the leukaemia can be kept under control for years, perhaps even decades.
In some people, CML doesn’t respond as well to treatment. And, in a few people, the leukaemia may progress from the chronic phase to a more advanced phase of the disease within about five years of diagnosis.
In a small number of people, the leukaemia may gradually move into an accelerated phase. In this phase there are more blast cells in the blood and bone marrow, and the leukaemia develops more quickly. Sometimes this change is picked up from your blood tests because the blasts can be seen when the blood is examined under a microscope. Or it may come to light because you develop new symptoms. If you feel unwell or develop new symptoms, let your doctor know straight away.
The treatment for the accelerated phase is often more intensive than in the chronic phase, and you may need to spend some time in hospital. Your specialist can give you more information about this.
After some time (usually months) in the accelerated phase, the leukaemia ‘transforms’ into a blast phase, which is more like an acute leukaemia. In this phase, there are many blast cells filling much of the bone marrow. There are also a lot more blasts found in the blood than normal.
Some people have CML that doesn’t respond to treatment. In this case, the leukaemia changes quickly from the chronic phase to the blast phase without going through the accelerated phase. The blast phase is also sometimes known as blast crisis.
Remission, or a complete response, is when the blood and bone marrow go back to normal following treatment. There are different levels of remission.
Relapse means that leukaemia cells have reappeared after a period of remission.
Content last reviewed: 1 February 2012
Next planned review: 2014
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© Macmillan Cancer Support 2013
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