The blood and chronic myeloid leukaemia (CML)

Leukaemia means a cancer of the blood forming system. The blood forming system is found in the bone marrow – the soft inner part of your bones. There is more information about the blood and circulation in the about cancer section of CancerHelp UK.

In most types of leukaemia, abnormal white blood cells are made in the bone marrow. These cells can get into the blood stream and circulate round the body. They do not work normally and so do not give you the protection from infection that they should. 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 of CancerHelp UK 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 more slowly than acute leukaemia. 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) in CancerHelp UK. There is also a section on hairy cell leukaemia if you are looking for information on this rarer type.

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. When your body needs them more, it 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 either a myeloid stem cell or a lymphoid stem cell. Myeloid stem cells eventually develop into

• Red blood cells (erythrocytes)
• Platelets (thrombocytes)
• White blood cells (granulocytes)

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.

New, immature blood cells of any type are called blasts. Some blasts stay in the bone marrow to mature. Some travel through the blood system to other parts of the body before they mature. Although they are not properly developed, even leukaemia cells mature to some extent. So it is possible to have very young leukaemic white blood cells – leukaemic blasts. In CML, the disease can enter a phase where it suddenly begins to develop more quickly. There is a sudden growth of leukaemia cells, with a lot of blasts in the bone marrow and blood. Doctors call this blast crisis. There is more about the different phases of CML in this section of CancerHelp UK.

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).

In some types of leukaemia, you don't make too many white blood cells, but they don't die when they should do. Blood cells have a normal life span and these leukaemic cells are living too long. The result is the same – more white blood cells than is normal.

There is more about the white blood cells, red blood cells and platelets and what they each do in the page on blood and circulation in the about your body section of CancerHelp UK. There is more about the symptoms of chronic myeloid leukaemia in this section.