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Three Phases of CML

CML typically begins in the chronic phase, and over the course of several years progresses to an accelerated phase and ultimately to blast crisis.

The progression of CML is described in three phases. The phase is determined by the number of white blood cells and the severity of symptoms. In addition, some of the white blood cells never mature and are called ‘blasts’. The percentages of these blast cells are also used to distinguish between the phases of CML.

Chronic phase

In the chronic phase, the leukaemia progresses very slowly and can be stable for long periods of time. There are 5% or fewer blast cells in the blood and bone marrow during this stage. The chronic phase lasts for about 4–6 years on average and it is during this time that most people are diagnosed. There may be a few mild symptoms and most people find they can lead a normal life.

People in this phase will have regular appointments to have their blood tested and will be given treatment as an outpatient.

Accelerated phase

After a while, the disease progresses more quickly and this phase is known as the accelerated phase. This is when there are 6–20% blast cells in the blood and bone marrow. During this time new symptoms may be experienced, or there may be a worsening of existing symptoms. These may include tiredness and loss of appetite, and bruising or bleeding may occur more easily. You should let your doctor know straight away if you become aware of any of these signs.

The treatment for this phase is more intensive, so people in this stage may need to spend some time in hospital as an inpatient. The accelerated phase usually lasts about 6–12 months, until it either responds to treatment or progresses to the next stage.

Blastic phase

In the blastic phase there are 20% or more blast cells in the blood or bone marrow. This means that much of the bone marrow has been replaced with very immature blast cells, which prevents the other blood cells from functioning normally. This phase is also called ‘blast crisis’ and normally lasts for 3–6 months.
In some people, CML appears to progress from the chronic phase straight to the blast phase, without going through the accelerated phase. In the blast phase, symptoms of tiredness, fever and an enlarged spleen may occur.

Last modified: 
27 March 2020