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The blood and chronic myeloid leukaemia (CML)

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This page tells you about the blood and chronic myeloid leukaemia (CML). There is information about


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Chronic myeloid leukaemia (CML)

Leukaemia is a blood cancer. It affects the white blood cells. White blood cells are part of our immune system and normally protect us from infection. In leukaemia the white blood cells are abnormal and they don't give the protection from infection that they should. 

In chronic myeloid leukaemia (CML) the bone marrow makes too many of a certain type of white blood cell called granulocytes. So CML is sometimes also called chronic granulocytic leukaemia or CGL. 

The bone marrow can't produce enough healthy blood cells, such as red blood cells or platelets. The abnormal white blood cells can build up in the lymph nodes, bone marrow and spleen, and cause swelling in these areas. They may also cause problems in the liver, brain or spinal cord.

Chronic leukaemia tends to take a very long time to develop. You may have it for months or years without having many symptoms. It may be stable for months or years before it gets worse. 


CR PDF Icon You can view and print the quick guides for all the pages in the About CML section.



What leukaemia is

Leukaemia is a blood cancer. It affects the white blood cells. Our blood cells are formed in the bone marrow - the soft inner part of our bones. There is detailed information about the blood and circulation in the about cancer section.

In leukaemia, abnormal white blood cells are made in the bone marrow. White blood cells normally circulate round the body in the bloodstream and protect us from infection. But in leukaemia the cells do not work normally and so don't protect from infection. Because there are too many of these abnormal white blood cells, they can build up in the lymph nodes, bone marrow and spleen and cause swelling in these areas. They can also cause problems in the liver and central nervous system.

There are several types of leukaemia, but two main groups

  • Acute leukaemia
  • Chronic leukaemia

Leukaemia is called acute or chronic depending on how fast it develops and gets worse. If you are looking for information about acute leukaemia, this is not the right section for you. There is information about the different types of acute leukaemia in the leukaemia section. This section is only about chronic myeloid leukaemia (CML) in adults.

Chronic leukaemia tends to develop very slowly. You may have a chronic leukaemia for months or years without having many symptoms. It may be stable for months or years before it gets worse. 

There are 2 main types of chronic leukaemia. There is information about chronic lymphocytic leukaemia (CLL). There is also a section on hairy cell leukaemia if you are looking for information on this rarer type.


Blood cells and leukaemia

To understand why leukaemia affects you the way it does, it helps to know how blood cells are normally produced and what they do.

Normally, blood cells are produced in the bone marrow. The body makes them in a controlled way. All blood cells start as the same type of cell, called a stem cell. This earliest stem cell then develops into 

  • Red blood cells (erythrocytes)
  • Platelets (thrombocytes)
  • White blood cells (granulocytes, monocytes or lymphocytes)

Diagram showing how blood cells are made

It is the type of white blood cell that has become cancerous that tells you what type of chronic leukaemia you have. In chronic myeloid leukaemia (CML), it is the granulocyte white blood cells that are cancerous. So you may also hear CML called CGL or chronic granulocytic leukaemia.

Diagram showing which cells CML can start in


What blasts are

Immature blood cells are called blasts. In CML, the disease can enter a phase where it suddenly begins to develop more quickly. There is a sudden increase of leukaemia cells, with a lot of myeloid blasts in the bone marrow and blood. Doctors call this blast crisis. There is more about the different phases of CML in this section.


How leukaemia affects the blood cells

White blood cells help to fight infection. So if you have abnormal white blood cells, you have less protection against infection. You may get a lot of infections and they may be difficult to get rid of.

When you have too many white blood cells, they take up more room in the bone marrow than normal. So there is not enough space for making red blood cells and platelets. Red blood cells carry oxygen round the body. If you do not have enough of these, you will be tired and breathless. Doctors call this anaemia (pronounced uh-nee-me-uh).

Platelets are vital for normal blood clotting. If you have too few platelets, you will have bleeding problems such as nosebleeds, very heavy periods or a fine rash of red spots caused by bleeding into the skin. Doctors call this rash petechia (pronounced pe-tee-kee-uh).

There is information about the white blood cells, red blood cells and platelets and what they do on our page about the blood and circulation. There is information about the symptoms of chronic myeloid leukaemia in this section.


The Philadelphia chromosome

Most people with CML have an abnormal chromosome called the Philadelphia chromosome. All body cells contain chromosomes. There are 23 pairs of chromosomes in human cells. Each chromosome has a number from 1 to 23. Chromosomes are made up of thousands of genes. These are a bit like an instruction manual for building the body and keeping it healthy. 

The Philadelphia chromosome is when a gene called the ABL gene on chromosome 9 breaks off and sticks to a gene called the BCR gene on chromosome 22. This produces a new gene called BCR-ABL. This is called a fusion gene. The changed chromosome 22 with the new BCR-ABL gene on it is the Philadelphia chromosome. 

This process is called chromosomal translocation. It is a known type of genetic abnormality but not something that is inherited. So you were not born with it and it can't be passed on to your children. 

The Philadelphia chromosome makes the cell produce a protein that encourages leukaemic cells to grow and multiply. 


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Updated: 11 November 2014