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CML phases: chronic, accelerated and blast crisis | CION Cancer Clinics
CML has three phases. In chronic phase, blasts are under 10% of cells in the blood or marrow. In accelerated phase they are roughly 10 to 19%, and in blast crisis 20% or more. Most people are diagnosed in chronic phase and stay there on a daily tablet. This page explains how your phase is decided and what it changes. At CION Cancer Clinics, every leukaemia, MDS and MPN case is reviewed by our haematologist and discussed at a tumour board before a plan is agreed.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- What do the three CML phases mean?
- How are chronic, accelerated and blast phases different?
- Which tests decide your phase?
- What suggests CML is steady, and what suggests it is moving?
- What do people often misread about CML phases?
- What does your phase not tell you on its own?
- Common questions about CML phases
The short answer
What do the three CML phases mean?
CML is described in three phases: chronic, accelerated and blast crisis. The phase tells you how far the disease has moved, and it is mostly decided by the share of very young cells, called blasts, in your blood or marrow.
Most people are in chronic phase
The large majority of people are diagnosed in chronic phase. The marrow is overactive, but the cells it makes still mature and mostly do their jobs. This is the phase where a daily tablet works best, and where most people stay for many years once treatment starts.
Phases are not like cancer stages
You may be used to hearing about stage 1 to 4 for other cancers. CML does not work that way, because it is in the blood and marrow from the start. There is no lump to measure. The phase describes how the disease is behaving, not where it has spread.
The names are changing
Recent international guidelines have started to drop the accelerated phase as a separate label and to talk about high-risk features instead. Some reports still use all three names. Both describe the same idea: whether the disease is steady or moving forward. If your report and your doctor seem to use different words, ask which system the laboratory followed. The treatment decision does not change because of the label alone.
If your report does not name a phase, ask your haematologist which one applies to you. It shapes the whole plan.Side by side
How are chronic, accelerated and blast phases different?
The blast figures below are the ones widely used on reports. Laboratories and guidelines differ slightly.
Chronic phase
Blasts make up less than 10% of the cells in blood or marrow. Many people have few or no symptoms. Some feel tired or notice a swollen spleen under the left ribs.
Usually treated with
- A daily TKI tablet at home
- Regular BCR-ABL blood tests
Accelerated phase
Blasts make up roughly 10 to 19% of cells, or other warning signs appear, such as new chromosome changes or counts that stop responding. Symptoms are more common.
Usually means
- Closer monitoring
- Often a stronger or different TKI
- An early talk about transplant
Blast crisis
Blasts make up 20% or more of cells, or they form a mass outside the marrow. The disease now behaves like an acute, fast-growing leukaemia.
Usually means
- Hospital-based treatment
- A TKI plus chemotherapy
- Referral to a transplant centre
Not sure whether this applies to you?
Ask an oncologistWorking it out
Which tests decide your phase?
Complete blood count
Measures white cells, platelets and haemoglobin, and a smear shows the share of blasts and other young cells in the blood.
Bone marrow test
A sample from the hip bone gives a truer blast count than blood alone, and shows how crowded the marrow has become.
Chromosome study
Called cytogenetics. It confirms the Philadelphia chromosome and looks for extra changes that can signal a higher-risk disease.
Examination and history
Your doctor feels for a large spleen and asks about fevers, bone pain and weight loss. The phase is read from all of it together.
Signs to know
What suggests CML is steady, and what suggests it is moving?
Usually a steady picture
Worth telling your team soon
Blood counts back in range after treatment starts
Counts rising again while you take the tablet daily
BCR-ABL level falling or staying low
BCR-ABL level climbing on repeat tests
Spleen shrinking, energy returning
Spleen growing again, new bone pain or night sweats
No new blasts on the blood film
Blasts reported where there were none before
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One thing that cannot wait
If you have CML and develop a high fever, bleeding or bruising you cannot explain, severe breathlessness or sudden confusion, go to the nearest emergency department or call 108 the same day. These can mean very low healthy counts. Say you have CML, and bring your latest blood report.
Commonly believed
What do people often misread about CML phases?
"Chronic phase means it is harmless, so treatment can wait."
Chronic phase is the best time to treat, not a reason to delay. Starting the tablet early and taking it daily is what keeps most people from moving to a later phase.
"Once it moves to a later phase, nothing more can be done."
Treatment options still exist. Some people in accelerated phase return to chronic phase with a different TKI. Blast crisis is serious and harder to control, and a plan is still made for it.
"Feeling well means the phase has not changed."
Early change often shows on a blood test before you feel anything. This is why skipping tests to save time or money is risky, even when you feel fine.
"Every CML moves through all three phases in turn."
It does not. With steady treatment, most people in chronic phase never reach a later phase. A few are diagnosed directly in a later phase.
Being straight with you
What does your phase not tell you on its own?
The phase is one piece of the picture. It does not tell you how long anyone will live, or exactly how you will respond to treatment. Two people in chronic phase can do very differently depending on their risk features and how their BCR-ABL level falls.
Risk scores sit alongside the phase
Your haematologist may mention a risk score, such as Sokal or ELTS. These use your age, spleen size, platelets and blast count at diagnosis to sort chronic phase into lower and higher risk groups. They help choose the first tablet. They are not a prediction for you as a person.
Who the chronic phase picture does not fit
If you were diagnosed in accelerated phase or blast crisis, much of what you read about living normally on a tablet applies later, if at all. Your first months will be more intense, and a transplant centre may be involved early. Ask your team to explain your own plan.
Questions worth asking at your next visit
Which phase am I in, and how sure are you? Was a marrow test and a chromosome study done, or only blood tests? Is my risk score lower or higher? What result on my next BCR-ABL test would make you change the plan? Writing the answers down helps, especially if another family member is sharing the decisions with you.
CION's haematology team reviews your reports and presents your case at a tumour board. Transplant and specialised tests are arranged with qualified centres.Questions we are asked
Common questions about CML phases
Can CML go back from accelerated phase to chronic phase?
Sometimes, yes. When a TKI works well, blast counts can fall and the disease can settle back into a chronic-phase pattern. Your team will still watch more closely afterwards, because having been in a later phase is a risk feature. They may also discuss transplant while things are steady.
How quickly does chronic phase turn into blast crisis?
There is no fixed timeline. Without treatment, CML tends to move forward over years. With a TKI taken every day and regular testing, most people stay in chronic phase. Missed doses and missed tests are the most common avoidable reasons for trouble.
Do I need a bone marrow test to know my phase?
Usually, at diagnosis. The marrow gives a more accurate blast count and allows a full chromosome study. Later, many people are followed with blood tests alone. A repeat marrow test is asked for if results change or treatment is not working as expected.
My report says chronic phase but high risk. What does that mean?
It means you are in the early phase, but some features at diagnosis suggest a higher chance of a slower response. Your haematologist may choose a particular tablet or test more often. It is not a verdict. Many higher-risk people respond well.
Is blast crisis the same as acute leukaemia?
It behaves like one. The blasts can be myeloid, like AML, or lymphoid, like ALL, and that type guides treatment. It still carries the BCR-ABL gene, so a TKI is usually part of the plan, alongside chemotherapy and a referral for transplant.
Will I feel it if my phase changes?
Not always at first. Some people notice fevers, night sweats, bone pain, weight loss or a fuller left side. Others feel nothing, and the change shows only on a blood test. That is why regular tests matter even when you are well.
Does my phase decide whether I need a transplant?
It is a big part of it. In chronic phase, transplant is rarely needed early. In accelerated phase or blast crisis, or when several tablets fail, it is discussed sooner. Your age, general health and donor options also matter.
Can I get a second opinion on my phase?
Yes, and it is reasonable to ask. Bring the blood film, marrow and chromosome reports, and the slides if the lab can release them. Call the helpline and our haematology team will review what has been found so far.
Your Haematologist
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- National Cancer Institute — Chronic Myelogenous Leukemia Treatment (PDQ) - Patient Version
- American Cancer Society — Chronic Myeloid Leukemia (CML)
- Cancer Research UK — Chronic myeloid leukaemia (CML)
- Leukemia & Lymphoma Society — Chronic Myeloid Leukemia
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
CML Explained: A Cancer Managed Like a Chronic IllnessStart here if CML is new to youWhen CML Progresses to Blast CrisisWhat treatment looks like in the later phaseReading Your BCR-ABL Report and the IS ScaleThe blood test that shows whether CML is steadyCML Treatment Milestones at 3, 6 and 12 MonthsThe targets set in the first year
Talk to us
Not sure which phase your report shows?
Send us your blood and marrow reports. Our haematology team will read them with you and explain what they mean for your plan. One helpline serves every CION centre.