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Three Phases of CML

CML for most people typically begins in the chronic phase, and if not treated, over the course of 3 to 5 years progresses to accelerated phase and ultimately to blast phase/blast crisis which is akin to an acute leukaemia.

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, a population of the white blood cells do not mature and are called ‘blasts’. The percentages of blast cells are also used to distinguish between the three phases of CML.

Chronic phase

In the chronic phase, the disease progresses very slowly and can be stable for long periods of time- typically from 3 - 5 years. There are 0% to <5% blast cells present in the blood and bone marrow during this earlier stage. The chronic phase lasts from about 2–5 years on average and it is during this time that the majority of people are diagnosed. There may be none to a few mild symptoms that are often attributed to other common health issues.

People in chronic phase (CP) will have regular appointments to have their blood tested and will be given treatment on an outpatient basis.

Accelerated phase

After a while, if TKi therapy is not available or is poorly managed the disease can progress to a phase is known as accelerated phase (AP). This is when there are 6–20% blast cells evident in the blood and/or bone marrow. During this time new symptoms may be experienced, or there may be a worsening of existing symptoms. These may include fatigue and loss of appetite, night sweats, unexplained bruising or bleeding. You should let your doctor know straight away if you develop of any of these symptoms.

The treatment for accelerated phase in some is more intensive, so people diagnosed in AP may be admitted to hospital as an inpatient. The accelerated phase usually lasts about 6–12 months, until it either responds to treatment or progresses to the blast stage.

Blastic phase

In the blastic phase there are >20% blast cells in the blood or bone marrow. This means that much of the bone marrow has been replaced with immature blast cells, which prevents the other normal blood cells from functioning normally. This phase is also called ‘blast crisis’ and normally lasts for 3–6 months.
In a very small percentage of people, CML can progress from the chronic phase straight to the blast phase, without going through the accelerated phase. In the blast phase, more serious and difficult to control symptoms are evident. Blast Phase will need intensive medical intervention to try to get the patient back to 2nd chronic phase to enable preparation for stem cell transplantation in those with an HLA matched donor.

Last modified: 
23 July 2021