Chronic myeloid leukaemia (CML) is a condition where cells in the bone marrow that normally develop into white bloods cells such as neutrophils, basophils, eosinophils, and monocytes don’t develop properly and become abnormal. These abnormal cells grow and divide at a higher rate than normal cells. They also do not die when they become old or damaged like normal cells do. This is why CML is sometimes referred to as a blood cancer. CML is also called chronic myelogenous, chronic granulocytic or chronic myelocytic leukaemia.1
CML usually progresses slowly so symptoms may not appear for a long time. In Europe about half of people are diagnosed without any symptoms through routine blood tests. CML can have the following signs and symptoms:2
Nearly all the cells in the body contain chromosomes, made up of genes. Genes are the coded instructions in cells for making new cells and controlling how cells behave. Sometimes a part of one chromosome breaks off and switches places with a piece from another chromosome (called a “translocation”). In CML, parts of the BCR gene on chromosome 22 swaps parts with the ABL1 gene on chromosome 9. A new fusion gene called BCR-ABL1 is formed. This gene is located on a new shortened chromosome 22, which is called the Philadelphia (Ph) chromosome.
This Ph chromosome triggers the cell to make a protein (called a ‘BCR-ABL transcript’ or a ‘tyrosine kinase’) that encourages abnormal white blood cells to grow. The Ph chromosome is detectible in 95 out of 100 people with CML and all people diagnosed with CML will have the BCR-ABL1 fusion gene. However, we currently don’t know why this translocation happens.
Diagnosis of CML is generally straightforward and can be done with a blood test. Confirmation of diagnosis is then done by identifying the Philadelphia chromosome or the BCR-ABL1 tr anscript, or both, in the blood or bone marrow cells.
The average age at diagnosis in Europe is between 60 and 65 years. Many people are diagnosed at a younger age, but it is rare in children. The reason that some people develop CML is not known.
CML cells are unstable and without effective treatment they easily develop further abnormalities.2 This is what causes the disease to progress.