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Chronic myeloid leukaemia (CML) is a form of blood cancer, which affects the white blood cells known as myeloid cells. It is a slowly progressing form of leukaemia.
Blood cells are formed in the bone marrow, which is a spongy tissue found inside the bones. Blood-forming stem cells divide to produce either more stem cells or immature cells that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.
Chronic myeloid leukaemia (CML) affects myeloid-cell-producing stem cells. A myeloid stem cell becomes one of three types of mature blood cells:
People with CML produce too many granulocytes. The granulocytes aren't fully developed and are poorly functioning. Over time, the unhealthy cells accumulate and begin to fill up the bone marrow, preventing it from producing healthy blood cells.
Chronic leukaemia progresses slowly but, although it can be treated, it is not usually possible to cure chronic leukaemia with standard treatments.
Many patients with CML have no symptoms at the time they are diagnosed. Their CML is discovered following a blood test as part of a routine check-up or for another condition.
There are no specific signs or symptoms which would allow a diagnosis of CML to be made. The most common signs and symptoms are caused by the bone marrow being unable to produce enough normal blood cells.
Other signs and symptoms which may occur include:
CML is often a chance finding during when a blood sample has been taken for another condition or as part of a routine check-up. Most patients with CML will have bone marrow samples taken to confirm the diagnosis and to help to determine exactly what type of leukaemia a patient has.
An important test in CML looks for a specific abnormality in the chromosomes of the CML cells. This is not an inherited genetic abnormality because it is not found in non-leukaemia cells. This is called the Philadelphia chromosome and is formed when chromosome 9 and chromosome 22 swap over part of their DNA. The swap-over forms an abnormal “fusion” gene called BCR-ABL. The BCR-ABL gene is responsible for the abnormal behaviour of CML cells. BCR-ABL is also the target for the newest forms of treatment. Only about 1 in 20 patients with CML does not have the BCR-ABL gene – this is called atypical CML. The amount of the protein produced by the BCR-ABL gene can be measured in the blood and is a very good way to monitor the response to treatment.
Usually, a chest x-ray will be taken and also scans, to look for swollen lymph nodes, or other affected sites. Blood samples will be taken to test for any problems with the liver, kidneys or other organs. Some blood tests and scans will be repeated to check for the response to treatment and any complications. Other tests are usually only done at diagnosis.
Other tests which may be done include:
Blood tests and bone marrow samples may be repeated during treatment to monitor response.
There is no staging in CML, unlike in many forms of cancer. This is because CML is spread throughout the body at the time of diagnosis. There are three recognised phases of CML called chronic phase, accelerated phase and blast crisis. Before there were effective treatments almost all patients progressed from chronic to accelerated or blast phase. Modern treatments are very effective at preventing this progression.
There are systems for risk-scoring of CML. These are mainly used in clinical trials and in deciding what treatment to recommend.
If you are being treated for any type of leukaemia, you may be asked to consider taking part in a clinical trial. Clinical trials are scientific studies to find the best treatment; you can find more information on our website here.
Almost all patients with CML start treatment immediately after diagnosis. The main exceptions would be very elderly or frail patients who may be too unfit to tolerate treatment.
CML is not considered curable with standard treatments; with the possible exception of stem cell transplants in a small number of younger and/or fitter patients. Even though it is not curable, a new class of drugs called tyrosine kinases (TKIs) have transformed treatment of CML. Most patients with CML can now expect long survival with a good quality of life. There are three TKIs currently used in the UK, imatinib (Glivec®), nilotinib (Tasigna®) and dasatinib (Sprycel®).
The main ways in which CML is treated are:
Targeted therapy using TKIs is now the most widely used treatment for CML. This treatment has transformed the outlook for CML patients. Before TKIs were introduced the average survival after diagnosis was about seven years. Now it is expected that many, probably most, CML patients will have a normal or near-normal life-expectancy.
Chemotherapy is the use of cell-killing drugs. These kill the cancer cells and/or stop them from dividing. Chemotherapy is usually given in blocks or ‘cycles’ of treatment. One cycle of treatment will consist of a series of doses of chemotherapy followed by a break for the healthy cells to recover.
Chemotherapy is normally given as a combination of drugs. There are various drugs and combinations which can be used for patients whose CML does not respond to TKIs. Patients will be given a chance to discuss treatment options and detailed information on their treatment plan before it starts. The side effects of treatment vary between different types of treatment and different patients.
Before the introduction of TKIs a stem cell transplant was the preferred treatment for any patient who was fit enough and had a well matched donor. This treatment is now reserved for young fit patients who have a fully matched sibling (brother or sister) who can donate healthy stem cells.
Patients will be given detailed information about any likely side-effects before treatment starts.
We understand going through a blood cancer through journey can be difficult. It may help to talk to a close friend or relative about how you are feeling. Here are some questions that may be useful to ask your doctor.
A Facebook group exists called CML UK, for CML patients and carers to chat on an informal basis, ask questions and support each other.
The group has been set up by Nigel Deekes, a CML patients and patient advocate, who found there to be very little support online for CML patients.
The group is a closed group, so content can only be seen by members.
If you would like to join, visit the page and request to join.