Staging of chronic myelogenous leukemia

Staging is a way of describing or classifying a cancer based on the extent, or amount, of cancer in the body. Cancers that form solid tumours are given numbered stages based on the size of the tumour and if the cancer has spread to lymph nodes or other parts of the body.

Chronic myelogenous leukemia (CML) is not staged in the same way as other types of cancer because it is a cancer of the cells in the blood-forming tissue in the bone marrow and doesn’t form a solid tumour. Instead of stages, CML is given a phase based on blood cell counts and symptoms.

Phases of CML

CML usually progresses through each of these phases. Sometimes it can progress from the chronic phase directly to the blast phase. Most people are diagnosed in the chronic phase, but sometimes the blast phase is the first sign of CML.

Chronic phase

In the chronic phase:

  • less than 5% of the cells in the blood and bone marrow are immature blood cells (called blast cells, or blasts)
  • there are no symptoms or symptoms are very mild
  • the disease progresses slowly in general (it may be several years before it advances to the next phase)
  • the disease usually responds well to treatment

Accelerated phase

In the accelerated phase, any of the following apply:

  • 10%–19% of the cells in the blood or bone marrow are blast cells
  • there are symptoms, including fever, poor appetite, weight loss, and the spleen is larger than normal
  • the blast cells often have new chromosome changes in addition to the Philadelphia (Ph) chromosome
  • at least 20% of the white blood cells in the blood and bone marrow are basophils
  • the number of platelets in the blood is very high or very low
  • the disease doesn’t respond to treatment as well as it did in the chronic phase

When leukemia is in the accelerated phase, it can quickly progress to the blast phase. When this happens, it is called a blast crisis.

Blast phase

The blast phase is also called the acute phase or blast crisis. In this phase, the CML acts more like an acute leukemia:

  • more than 20% of cells in blood and bone marrow are blast cells, or blasts
  • the abnormal cells spread to tissues and organs outside the bone marrow
  • there are symptoms, including fever, malaise, an enlarged spleen, poor appetite, weight loss, fatigue, shortness of breath, abdominal pain and bone pain
  • white blood cell counts and platelet counts become very abnormal (this can lead to bleeding and infections)

Relapsed CML

Relapsed, or recurrent, CML means that the number of blast cells in the blood and bone marrow increase after treatment and reaching remission. Remission means that the blood cell counts have returned to normal and stay at or near normal levels for long periods of time.


Refractory disease means the leukemia did not respond to treatment.

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