Chronic myeloid leukaemia (CML)
What is CML?
Chronic myeloid leukaemia (CML) is a type of cancer that affects the blood and bone marrow. In CML the bone marrow produces too many white cells, called granulocytes. These cells (sometimes called blasts or leukaemic blasts) gradually crowd the bone marrow, interfering with normal blood cell production. They also spill out of the bone marrow and circulate around the body in the bloodstream. Because they are not fully mature, they are unable to work properly to fight infections. Over time, a shortage of red cells and platelets can cause anaemia, bleeding and/or bruising.
CML usually develops gradually during the early stages of disease, and progresses slowly over weeks or months. It has three phases:
- chronic phase
- accelerated phase
- blast phase.
Most people (more than 90%) are diagnosed in the early chronic phase of CML. Blood counts remain relatively stable and the proportion of blast cells in the bone marrow and blood is low (five per cent or less). Most people are generally well at this stage and have few, if any, troubling symptoms of their disease. For most people these days, the duration of this phase is substantially longer than five years, and may exceed 10-15 years.
After some time and despite treatment, CML begins to change from a relatively stable disease into a more rapidly progressing one. This is known as the accelerated phase of CML. During this time a proportion of blast cells may start to increase in your bone marrow and circulating blood.
Eventually, CML transforms into a rapidly progressing disease resembling acute leukaemia. This is known as the blast phase or blast crisis. It is characterised by a dramatic increase in the number of blast cells in the bone marrow and blood (usually 30% or more) and by the development of more severe symptoms of your disease. In about two-thirds of cases, CML transforms into a disease resembling acute myeloid leukaemia (AML). The remainder transforms into a disease resembling acute lymphoblastic leukaemia (ALL). Occasionally, the blast cells are said to be undifferentiated or mixed.
How common is CML?
Each year in Australia around 330 people are diagnosed with CML. Overall, CML is a rare disease, accounting for around 0.03% of all cancers diagnosed.
Who gets CML?
CML can occur at any age but it is more common in adults over the age of 40, who account for nearly 70% of all cases. CML occurs more frequently in men than women and is rarely diagnosed in children.
What causes CML?
We know that CML is not inherited (passed down from one generation to the next) or contagious. Like other types of leukaemia, CML is thought to arise from an acquired mutation (or change) in one or more of the genes that normally control the growth and development of blood cells. This change or changes will result in abnormal growth.
Most people diagnosed with CML have a genetic abnormality in their blood cells called the Philadelphia (Ph) chromosome. The Ph-chromosome causes the production of an enzyme called tyrosine kinase which leads to CML. Why these mutations occur in the first place remains unknown but there are likely to be a number of factors involved. Research is going on all the time into possible causes of this damage and certain factors have been identified that may put some people at an increased risk. These include exposure to:
- radiation — very high doses of radiation, either accidentally (nuclear accident) or therapeutically (to treat other cancers)
- chemicals — exposure to industrial chemicals like benzene over a long period of time, or exposure to certain types of chemotherapy to treat other cancers.
What are the symptoms of CML?
Because CML develops slowly many people don’t have any symptoms (particularly in the early stages) and the disease is picked up on a routine blood test.
As the disease progresses, symptoms arise from the increasing number of abnormal blood cells in the bone marrow and blood, and the decreasing number of normal blood cells. Possible symptoms may include:
- anaemia, due to a lack of red cells and causing persistent tiredness, dizziness, paleness, or shortness of breath when physically active
- increased or unexplained bleeding or bruising, due to a very low platelet count
- frequent or repeated infections and slow healing, due to a lack of normal white blood cells
- pain or discomfort under the ribs on the left side, due to an enlarged spleen
- excessive sweating or unintentional weight loss.
Some of the symptoms described above may also be seen in other illnesses, including viral infections. Therefore, most people with these symptoms don’t have leukaemia. However, it is important to see your doctor if you have any unusual symptoms, or symptoms that persist much longer than expected so that you can be examined investigated properly.