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Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML)

  • Is a cancer of the bone marrow and blood
  • CML is usually diagnosed in its chronic phase when treatment is very effective for most patients
  • CML has three phases

Click here to access CML statistics. 

What You Should Know

  • Chronic myeloid leukemia (CML) is also called chronic myelogenous leukemia, chronic granulocytic leukemia and chronic myelocytic leukemia. CML is one of four main types of leukemia.
  • Hematologists and oncologists are specialists who treat people who have CML or other types of blood cancer.
  • Most CML patients are treated with daily oral drug therapy.
  • Since the introduction of tyrosine kinase inhibitor (TKI) therapy in 2001, CML has been transformed from a life-threatening disease to a manageable chronic condition for most patients. People are living longer with CML and experiencing fewer treatment side effects.

What You Should Do

  • Talk with your doctor about your diagnostic tests and what the results mean.
  • Make sure your doctor continually monitors your response to medication, which is essential to bringing your CML under control.

To download lists of suggested questions to ask your healthcare providers, click here.


How Does CML Develop?

The DNA (genetic material) of a developing stem cell in the bone marrow is damaged. This is called an “acquired mutation.”

  • Stem cells form blood cells (red cells, white cells and platelets).

This damaged cell becomes a leukemic cell and multiplies into many CML cells. The CML cells grow and survive better than normal cells.

  • CML doesn't completely interfere with the development of mature red cells, white cells and platelets. Therefore, chronic phase CML is generally less severe than acute leukemia.

As a result, the number of healthy blood cells (red cells, white cells and platelets) is usually lower than normal.

  • Anemia is a condition when there is a low number of red cells in the blood which can cause fatigue and shortness of breath.
  • Neutropenia is a condition when there is a low number of white cells so that the immune system can't effectively guard against infection due to a lack of neutrophils (a type of white cell).
  • Thrombocytopenia is a condition when there is a low number of platelets which can cause bleeding and easy bruising with no apparent cause.
  • Low numbers of all three blood cell counts is called pancytopenia.

The Philadelphia Chromosome and the BCR-ABL1 Fusion Gene

Sometimes errors occur during the process of a cell copying itself or dividing into new cells. One type of error is called a “translocation.” A translocation occurs when a piece of one chromosome breaks off and attaches to another chromosome. This can result in a “fusion gene,” an abnormal gene that is formed when two different genes are fused together.

All cases of CML are caused by the BCR-ABL1 fusion gene. This gene is not found in normal blood cells. 

The BCR-ABL1 gene is formed by a translocation between parts of chromosomes 9 and 22 in a single bone marrow cell during cell division. The abnormal chromosome 22 is called the Philadelphia chromosome (Ph chromosome). More than 95 percent of CML patients have the Ph chromosome. 

Genes provide instructions for making proteins. The BCR-ABL1 oncogene produces an abnormal protein called "BCR-ABL1 tyrosine kinase," which leads to the development of CML cells.

For more information please refer to the free information booklet, Chronic Myeloid Leukemia.

Risk Factors

For most people who have chronic myeloid leukemia (CML), there are no obvious reasons why they develop the disease. No one is born with CML. It happens when there is an injury to the DNA of a single bone marrow cell. Risk factors for CML are:

  • Sex- CML is slightly more common in males than females.
  • Age - The risk of getting CML increases with age.
  • Radiation exposure - In a small number of patients, CML is caused by exposure to very high doses of radiation (such as being a survivor of an atomic bomb blast or a nuclear reactor accident). A slight increase in risk also occurs in some individuals treated with high-dose radiation therapy for other cancers, such as lymphoma. Most people treated for cancer with radiation do not develop CML, and most people who have CML have not been exposed to high doses of radiation. Exposures to diagnostic dental or medical x-rays have not been associated with an increased risk of CML.

Source: Chronic Myeloid Leukemia. Reviewed by Michael Deininger, MD, PhD