Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 17 peer-reviewed journal articles Updated
Oncology

The Phases of CML: Understanding Disease Progression

At a Glance

Chronic Myeloid Leukemia (CML) is classified into phases based on the percentage of immature white blood cells called blasts. Over 90% of patients are diagnosed in the highly treatable Chronic Phase, and modern medications make progression to the advanced Blast Phase very rare.

Chronic Myeloid Leukemia (CML) is a disease that can change its behavior over time. Doctors use “phases” to describe how active the leukemia is and how many immature white blood cells—called blasts—are in your blood and bone marrow [1][2].

Understanding your phase is the first step in planning your care, as it helps your medical team determine how aggressive your treatment needs to be [3][4].

The Two Ways to Classify CML

Medical guidelines for CML have recently been updated, and you may hear your doctor use different terminology depending on which system they follow.

  • The Simplified View (WHO 2022): The World Health Organization recently updated its guidelines to simplify CML into just two phases: Chronic Phase and Blast Phase [5][6]. They removed the middle “Accelerated Phase” because modern medications (TKIs) are so effective at preventing the disease from progressing that this middle stage has become much rarer [7][8].
  • The Traditional View (ICC 2022): Another system, the International Consensus Classification, still uses a three-phase model that includes the Accelerated Phase [5].

Chronic Phase (CP)

About 90% to 95% of people are diagnosed in the Chronic Phase [3]. In this phase, your blood and bone marrow contain fewer than 10% blasts [1].

  • How it feels: Many people have no symptoms, while others may feel tired or notice fullness in their side (due to an enlarged spleen).
  • The Outlook: This phase is highly manageable. The goal of treatment is to keep you in the Chronic Phase indefinitely using daily oral medications (TKIs) [9][10]. For information on treatments, see Targeted Therapy.

Accelerated Phase (AP)

If your doctor still uses this term, it refers to a “middle ground” where the leukemia is beginning to behave more aggressively. It is typically defined by having 10% to 19% blasts, or other signs like a rising number of basophils (another type of white blood cell) or new chromosomal changes [1][11]. While this phase requires closer monitoring and sometimes a change in medication, it is still very treatable [5][12].

Blast Phase (BP)

The Blast Phase (sometimes called a “Blast Crisis”) is the most advanced stage of CML. It occurs when your blood or bone marrow has 20% or more blasts [1][2].

  • Behavior: In this phase, CML begins to act like an aggressive “acute” leukemia (such as AML or ALL) [5][13]. The leukemia cells stop maturing and rapidly crowd out healthy blood cells [14].
  • The Reassurance: While reading about the Blast Phase can be frightening, it is crucial to know that progressing to this phase is exceptionally rare today for patients who take their TKIs exactly as prescribed. Modern medications are highly effective at halting the disease in the Chronic Phase [7][8].
  • Treatment: This phase requires more intensive therapy, often involving a combination of TKIs and hospital-based chemotherapy [4][13]. For many patients in the Blast Phase, a stem cell transplant is the ultimate goal to achieve a long-term cure [15][4].

Monitoring for Progression

The primary goal of modern CML care is to stay in the Chronic Phase. Your medical team will use regular blood tests (RT-PCR) to measure your BCR-ABL1 levels [16]. As long as these levels remain low or continue to drop, it is a sign that the medication is working and the disease is not progressing [17][3].

Common questions in this guide

What are the different phases of CML?
CML is typically classified into either two or three phases, depending on the medical guidelines your doctor uses. The traditional system includes the Chronic, Accelerated, and Blast phases, while newer WHO guidelines simplify it to just the Chronic and Blast phases.
What does it mean to be in the Chronic Phase of CML?
Being in the Chronic Phase means your blood and bone marrow contain fewer than 10% blasts. This is the most common phase at diagnosis and is highly manageable with daily oral medications called TKIs.
What is a CML blast crisis?
A blast crisis, or Blast Phase, is the most advanced stage of CML where blasts make up 20% or more of your blood or bone marrow. In this phase, the disease behaves like an aggressive acute leukemia and requires intensive treatments like chemotherapy or a stem cell transplant.
How do doctors know if my CML is progressing?
Doctors monitor your disease using regular blood tests (RT-PCR) to check your BCR-ABL1 levels and the percentage of blasts. A sudden rise in these levels, increased basophils, or the appearance of new chromosomal changes can signal that the disease is advancing.
Will my CML definitely progress to the Blast Phase?
Progressing to the Blast Phase is extremely rare today for patients who take their prescribed targeted therapies correctly. Modern medications are highly effective at keeping the disease safely halted in the Chronic Phase indefinitely.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Am I being staged using the newer 2-phase system (WHO) or the 3-phase system (ICC)?
  2. 2.What was the exact percentage of 'blasts' in my blood and bone marrow at diagnosis?
  3. 3.Besides the Philadelphia chromosome, did my tests show any 'additional chromosomal abnormalities' that could signal a higher risk of progression?
  4. 4.If my disease is in the Chronic Phase, what specific blood count or molecular markers would signal that it is moving toward a more advanced phase?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    Chronic Myeloid Leukemia: A Review.

    Jabbour E, Kantarjian H

    JAMA 2025; (333(18)):1618-1629 doi:10.1001/jama.2025.0220.

    PMID: 40094679
  2. 2

    Immunohistochemistry in Acute Myeloid Leukemia.

    Cruise MW

    Methods in molecular biology (Clifton, N.J.) 2017; (1633()):33-49 doi:10.1007/978-1-4939-7142-8_3.

    PMID: 28735479
  3. 3

    Chronic Myeloid Leukemia, Version 1.2019, NCCN Clinical Practice Guidelines in Oncology.

    Radich JP, Deininger M, Abboud CN, et al.

    Journal of the National Comprehensive Cancer Network : JNCCN 2018; (16(9)):1108-1135 doi:10.6004/jnccn.2018.0071.

    PMID: 30181422
  4. 4

    Clinical outcomes of allogeneic cell transplantation for patients with chronic myeloid leukemia.

    McCormick B, Findley A, Diebold K, et al.

    Leukemia & lymphoma 2025; (66(14)):2717-2727 doi:10.1080/10428194.2025.2564766.

    PMID: 41070588
  5. 5

    Advanced-Stage Chronic Myeloid Leukemia: Options for Difficult Treatment Situations.

    Atallah E, Deininger M

    Drugs 2025; (85(1)):41-50 doi:10.1007/s40265-024-02108-2.

    PMID: 39638957
  6. 6

    Chronic Myeloid Leukemia, Version 2.2024, NCCN Clinical Practice Guidelines in Oncology.

    Shah NP, Bhatia R, Altman JK, et al.

    Journal of the National Comprehensive Cancer Network : JNCCN 2024; (22(1)):43-69 doi:10.6004/jnccn.2024.0007.

    PMID: 38394770
  7. 7

    Dasatinib-Induced Colitis with Rectal Sparing in a Patient with Chronic Myeloid Leukemia (Chronic Phase) on Dasatinib as an Upfront Therapy: Case Report.

    Maat Z, Mushtaq K, Yassin MA

    Case reports in oncology 2021; (14(3)):1441-1446 doi:10.1159/000516794.

    PMID: 34899234
  8. 8

    Pathogenesis and management of accelerated and blast phases of chronic myeloid leukemia.

    Senapati J, Jabbour E, Kantarjian H, Short NJ

    Leukemia 2023; (37(1)):5-17 doi:10.1038/s41375-022-01736-5.

    PMID: 36309558
  9. 9

    How I individualize treatment for chronic-phase CML.

    Leyte-Vidal AM, Shah NP

    Blood 2025; doi:10.1182/blood.2024026508.

    PMID: 40239150
  10. 10

    The issue of financial toxicity in the management of chronic myeloid leukemia with blast crisis.

    Eskazan AE

    Journal of medical economics 2018; (21(7)):709-711 doi:10.1080/13696998.2018.1467919.

    PMID: 29673265
  11. 11

    Clinical Validation of the Somatic FANCD2 Mutation (c.2022-5C>T) as a Novel Molecular Biomarker for Early Disease Progression in Chronic Myeloid Leukemia: A Case-Control Study.

    Alanazi N, Siyal A, Basit S, et al.

    Hematology reports 2024; (16(3)):465-478 doi:10.3390/hematolrep16030045.

    PMID: 39051418
  12. 12

    Blast and accelerated phase CML: room for improvement.

    How J, Venkataraman V, Hobbs GS

    Hematology. American Society of Hematology. Education Program 2021; (2021(1)):122-128 doi:10.1182/hematology.2021000240.

    PMID: 34889372
  13. 13

    Blast phase of chronic myeloid leukemia presenting as early T-cell precursor acute lymphoblastic leukemia.

    E S, Xu J, Wang SA, et al.

    American journal of clinical pathology 2025; (163(2)):231-239 doi:10.1093/ajcp/aqae115.

    PMID: 39235991
  14. 14

    Extramedullary Blast Crisis of Chronic Myelogenous Leukemia With a Skin Lesion: A Case Report and Literature Review.

    Qi J, Zhang F, Liu Y, et al.

    The American Journal of dermatopathology 2021; (43(6)):450-453 doi:10.1097/DAD.0000000000001897.

    PMID: 33481378
  15. 15

    The Contemporary Role of Hematopoietic Stem Cell Transplantation in the Management of Chronic Myeloid Leukemia: Is It the Same in All Settings?

    Elmakaty I, Saglio G, Al-Khabori M, et al.

    Cancers 2024; (16(4)) doi:10.3390/cancers16040754.

    PMID: 38398145
  16. 16

    European LeukemiaNet 2020 recommendations for treating chronic myeloid leukemia.

    Hochhaus A, Baccarani M, Silver RT, et al.

    Leukemia 2020; (34(4)):966-984 doi:10.1038/s41375-020-0776-2.

    PMID: 32127639
  17. 17

    Assessment of individual molecular response in chronic myeloid leukemia patients with atypical BCR-ABL1 fusion transcripts: recommendations by the EUTOS cooperative network.

    Schäfer V, White HE, Gerrard G, et al.

    Journal of cancer research and clinical oncology 2021; (147(10)):3081-3089 doi:10.1007/s00432-021-03569-8.

    PMID: 33677711

This page explains CML phases and disease progression for educational purposes only. Always consult your hematologist or oncologist to understand your specific phase, diagnosis, and monitoring plan.

Get notified when new evidence is published on Chronic myeloid leukemia.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.