The phases of CML

Female patient at a doctor's appointment

The tests that you have will help your doctor to ‘stage’ your CML.

Staging CML means finding out which phase it is in. The phases refer to how many blast/leukaemia cells are in your bone marrow. The more abnormal cells there are, the more symptoms you will have. This is because the blast cells crowd the bone marrow, affecting your ability to produce normal white blood cells to fight infection.

Know the phase helps your doctor to plan your treatment, as different phases need different treatments. 

CML can present in 3 phases. It usually presents in the chronic phase, less commonly in the accelerated phase and rarely in the blast phase.

The chronic (early) phase

Around 9 out of 10 people diagnosed with CML are in the chronic phase. In this phase the CML is developing very slowly. It can also be called a stable phase. Fewer than 1 in 10 (10%) of the blood cells in your bone marrow are blasts.

With medication (usually taking tablets at home), people with CML in the chronic phase usually live a normal life and have very few symptoms. Treatment may keep your CML in the chronic phase for a long time – maybe even for your whole life if you keep taking the medication.

The accelerated phase

In this phase, there are more immature blast cells present in your blood. Between 10% and 30% of the blood cells in your bone marrow are blast cells. You may develop new or more obvious symptoms if your CML enters this phase. For example, you may feel more tired than usual or you may lose weight. Read more about CML symptoms.

The blast phase

In this phase more than 30% of the blood cells in your bone marrow are blast cells and the blast cells may have spread to the blood and other organs. This phase is also called an acute phase or a blast crisis. This is when the leukaemia transforms into an acute leukaemia (usually acute myeloid leukaemia).

If your CML enters the blast phase you will probably have more serious symptoms such as pain in your tummy or bones, a swollen spleen, unusual bleeding such as bleeding gums and nosebleeds, and repeated infections.

With the right treatment, CML often stays in phase 1, the more stable, chronic phase. Read more about how the different phases are treated.

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