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CML Phases and Prognostic Factors

CML has three phases. The phase of your chronic myeloid leukemia (CML) plays a large part in determining the type of treatment you'll receive. Doctors use diagnostic tests to determine the phase of CML. Determining the CML phase is based primarily on the number of immature white blood cells (blasts) in the patient’s blood and bone marrow. 

Phases of CML

Chronic Phase. Most patients are diagnosed with CML in the with chronic phase of the disease.

​People with chronic phase CML:

  • May or may not have symptoms
  • Have an increased number of white blood cells
  • Usually respond well to standard treatment

If untreated, chronic phase CML will eventually progress to accelerated phase CML and/or blast phase CML.

Accelerated Phase. In the accelerated phase, the number of immature blast cells has risen, and sometimes new chromosomal changes, in addition to the Ph chromosome, will occur.

Criteria for diagnosing accelerated phase CML includes:

  • Bone marrow or peripheral blood blasts of 10%-19%
  • Peripheral blood basophils (a type of white blood cell) in the blood greater than or equal to 20%
  • Presence of additional chromosomal abnormalities in CML cells 

​In the accelerated phase, the number of CML cells grow faster and cause symptoms such as fatigue, fever, weight loss and an enlarged spleen. If untreated, accelerated phase CML will eventually transform to blast phase CML.

Blast Phase (Also Called "Blast Crisis Phase"). The blast phase appears and behaves like acute myeloid leukemia.

Criteria for diagnosing blast phase CML includes: 

  • Bone marrow or peripheral blood blasts greater than or equal to 20% 
  • Myeloid sarcoma – a rare type of cancer that is made up of myeloblasts (a type of immature white blood cell) and forms outside the bone marrow and blood
  • Presence of lymphoblasts (>5%) suggesting lymphoblastic crisis

People who have blast phase CML may have signs and symptoms such as fever, fatigue, shortness of breath, abdominal pain, bone pain, enlarged spleen, poor appetite and weight loss, night sweats, bleeding, and/or infections.

Prognostic Factors of CML

There are other factors, in addition to the phase of CML, that affect treatment decisions and can be used to predict a patient’s prognosis. These are called “prognostic factors.”

The following prognostic factors for patients with CML at the time of diagnosis are also associated with a less favorable prognosis:

  • Phase of CML—patients who have accelerated or blast phase CML compared to those who have chronic phase CML
  • Age—patients age 60 years and older
  • Spleen size—patients with an enlarged spleen
  • Platelet count—patients who have very high or very low platelet counts at diagnosis
  • Blasts in the blood—patients who have a high number of blasts in the blood
  • Patients with increased numbers of basophils

Many of these factors are used in prognostic scoring systems to predict outcomes for patients with CML. There are three prognostic scoring systems used to determine the risk profile of patients with chronic phase CML at the time of diagnosis. They are the:

  • Sokal scoring system
  • Hasford scoring system
  • European Treatment and Outcome Study for CML (EUTOS) Long-Term Survival scoring system (ELTS)

To learn more about these scoring systems, view LLS's free booklet Chronic Myeloid Leukemia

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