Chronic myeloid leukaemia (CML)
What is it?
Chronic myeloid leukaemia (CML) is a type 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: the chronic phase, the accelerated phase and the blast phase. These phases are distinguished by the number of blast cells (immature white cells) in the blood and bone marrow, and the severity of symptoms.
How common is it?
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 it?
CML can occur at any age but it is more common in adults over the age of 50, who account for nearly 70 per cent of all cases. CML occurs more frequently in men than in women. It is rare in children (0-14 years) with around 4 cases per year diagnosed in this age group.
What causes CML?
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. It is unclear why this genetic abnormality occurs in the first place, but there are likely to be a number of factors involved. In rare cases it may result from exposure to very high doses of radiation, either accidentally (nuclear accident) or therapeutically (to treat other cancers).
What are the symptoms?
Because CML develops slowly many people don't have any symptoms, particularly in the early stages and the disease is picked up during 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; causing persistent tiredness, dizziness, paleness, or shortness of breath,
- 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.
How is it diagnosed?
CML is diagnosed by a full blood count (FBC) and a bone marrow biopsy/examination.
How is it treated?
Treatment will vary depending on the phase of disease, general health and age. During the chronic phase, treatment is used to control CML and keep your blood counts within a normal range. This can involve chemotherapy, usually taken in tablet form at home.
Treatment is likely to involve the use of a type of tyrosine kinase inhibitor (TKI) - which blocks the leukaemia-causing effects of a substance called a tyrosine kinase, forcing the cell to then die. Commonly used tyrosine kinases available in Australia include: imatinib, nilotinib, and dasatinib. A stem cell transplant may be an option for some younger patients, or patients who are intolerant or resistant to TKIs - providing them with a better chance of cure.
In the accelerated phase, the disease starts to progress more quickly. Blood counts become more abnormal and symptoms develop. In the blast, or blast crisis phase, blood counts become very abnormal and the numbers of blast cells in the blood and bone marrow increase dramatically. The treatment of accelerated and blast phase CML usually involves a more intensive approach. This includes a combination of chemotherapy drugs given intravenously (into a vein). You need to be admitted to hospital for this type of treatment. The aim of treatment during the advanced stages of CML is to destroy the leukaemic cells and allow the bone marrow to function normally again, or to return the patient to the chronic phase of their disease.
Some people are diagnosed with an extremely high number of white cells in their blood. A process known as leukopheresis may be needed to remove these cells, which could otherwise cause problems in the body by clogging up small blood vessels. This process is similar to dialysis, where all your blood is passed through a special machine called a cell separator. This machine separates and collects the excess white cells and returns the rest of your blood to you. Chemotherapy is also used to reduce a high white cell count at diagnosis.
What are the side-effects of treatment?
All treatments can cause side-effects. The type and severity however will vary between individuals, depending on the type of treatment used and how an individual responds to it. In general, more intensive treatment is associated with more severe side-effects. It is important to report any symptoms you are having to your doctor or nurse. In most cases they can be treated and are reversible.
Your doctor and nurse will discuss with you the possible side-effects of your treatment and how they can be managed.