Chronic Myeloid Leukemia (CML)

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Chronic Myeloid Leukemia Facts

Leukemia begins in the bone marrow. Myelogenous, or myeloid, leukemias occur in bone marrow cells that normally become red blood cells, some white blood cells, and platelets.

Leukemia cells multiply just like other cells. But leukemia cells grow and survive better than normal cells and, over time, crowd out normal cells. The rate at which leukemia progresses and how the cells replace the normal blood and marrow cells are different with each type of leukemia.

When it’s acute, leukemia quickly prevents a large proportion of early blood cells from maturing. In chronic leukemia, more healthy blood cells get a chance to mature, so symptoms usually come on more gradually, and they are less severe at first.

How Is CML Different?

The leukemia cells in patients with chronic myeloid leukemia (CML) have the Philadelphia chromosome (Ph chromosome). Chromosomes are essential components in the nucleus of cells, and they contain genes that give instructions to the cells. The Ph chromosome is made when a piece of chromosome 22 breaks off and attaches to the end of chromosome 9. A piece of chromosome 9 also breaks off and attaches to the end of chromosome 22. The break on chromosome 9 involves a gene called Abl. The break on chromosome 22 involves a gene called Bcr. The Bcr and Abl genes combine to make the CML-causing gene called the Bcr-Abl cancer gene. Doctors do not know why or how this happens.

Three Phases of CML

There are three phases of CML.  At diagnosis, patients may be in any of the three phases, but most patients are in the chronic phase.

  1. The chronic phase. In the chronic phase, patients may have no symptoms, or they may have fevers, sweating at night, weight loss, fatigue and abdominal fullness from a large spleen. The white blood cells and sometimes the platelets are elevated in the blood. The percentage of blasts in the blood or bone marrow are not elevated. The white blood cells still fight infection, and after treatment people are able to continue their normal activities. 
  2. The accelerated phase. In the accelerated phase, patients may develop more or worse symptoms and have anemia and low platelet counts. The percentage of blasts may increase in the blood and bone marrow.
  3. The blast crisis phase. In the blast crisis phase, the number of blast cells in the marrow and blood are increased. This phase resembles acute leukemia. Patients often have anemia and low platelet counts. Patients may have infections or bleeding. They may also feel tired and have shortness of breath, stomach pain, or bone pain.


Leukemia symptoms begin like many other more common and less severe illnesses. People diagnosed with acute leukemia may experience symptoms such as the following:

  • Extreme tiredness
  • Shortness of breath during physical activity
  • Pale skin
  • Mild fever or night sweats
  • Slow healing of cuts
  • Excess bleeding
  • Bruises for no clear reason
  • Pinhead-size red spots under the skin called petechiae
  • Aches in bones or joints 
  • Low white cell counts, especially low monocytes or neutrophils

People diagnosed with chronic leukemias, like CML, may not notice any symptoms because the symptoms often come on gradually. Many people learn of their diagnosis after a regular check-up and blood test. When symptoms do appear, people with CML complain of tiredness, shortness of breath, fevers, night sweats, and weight loss.

If you are concerned about persistent symptoms such as a low-grade fever, unexplained weight loss, tiredness, or shortness of breath, see a healthcare provider.


A complete blood count (CBC) is used to diagnose leukemia. This blood test may show high or low levels of white cells and may show leukemic cells in the blood. Specific blood tests have been developed to detect the gene mutation, Bcr-Abl, diagnostic of CML. Bone marrow tests (aspiration and biopsy) are often done to confirm the diagnosis and to look for chromosome abnormalities. A complete blood exam and a number of other blood tests are used to determine the phase of CML and the extent of damage the disease has caused. These tests can be repeated after treatment begins to measure how well the treatment is working.

Risk Factors

There aren’t any real risk factors for most leukemias. Doctors do not know why the Bcr-Abl gene forms in some people but not in others.  Some risk factors that may increase the risk of developing CML include:

  • Exposure to very high doses of radiation 
  • High-dose radiation therapy used to treat other cancers

However, most people treated for cancer with radiation do not develop CML. And most people with CML were not exposed to high-dose radiation. There is no link between dental or medical X-rays and increased risk of CML.

You cannot catch CML from someone else.