Leukaemia

All blood cells are made in the bone marrow. Bone marrow is the spongy material in the middle of our bones. It is mainly in our pelvis and backbone (spine). There is a type of cell in the bone marrow called a blood stem cell. Blood stem cells can make any kind of blood cell your body needs.

There are two types of blood stem cell:

• lymphoid stem cells make a type of white blood cell called lymphocytes
• myeloid stem cells make all the other types of blood cells: red blood cells, platelets and other white blood cells.

Blood stem cells in the bone marrow divide and grow to make millions of new blood cells every day. The new blood cells are called blast cells. They are not fully developed and are known as immature. They cannot do the same jobs as mature cells. When blood cells are mature, they go into the bloodstream where they can do different jobs.

There are three main types of mature blood cells:

• white blood cells, which help us fight infection
• red blood cells, which carry oxygen from the lungs around our body
• platelets, which clot our blood to stop bleeding when we cut ourselves.

Usually, white blood cells divide and grow in a controlled way. In leukaemia, this process gets out of control. So the body makes too many immature blood cells. These do not develop into normal working blood cells.

These immature cells fill the bone marrow. This means there is not enough space to make all the healthy white cells, red cells and platelets your body needs.

The way leukaemia is named depends on the type of white blood cell it affects. It can be acute (faster growing) or chronic (slower growing). There are four main types of leukaemia:

• acute lymphoblastic leukaemia (ALL)
• acute myeloid leukaemia (AML)
• chronic lymphoblastic leukaemia (CLL)
• chronic myeloid leukaemia (CML)