Leukaemia is a cancer of the bone marrow. It affects the cells in the bone marrow that produce white blood cells.

The four main types of leukaemia are: chronic myeloid (CML), acute myeloid (AML), chronic lymphocytic (CLL) and acute lymphoblastic (ALL). Each type has its own characteristics and treatment.

Chronic myeloid leukaemia may also be called chronic granulocytic leukaemia or chronic myelogenous leukaemia. It is most common between the ages of 40 and 60 and is slightly more common in men than in women.

The bone marrow

Bone marrow is a spongy material that fills some of the bones and produces stem cells, which develop into the three different types of blood cells:

• red blood cells, which carry oxygen to all cells in the body
• white blood cells, which are essential for fighting infection
• platelets, which help the blood to clot and control bleeding.

All these cells normally stay inside the bone marrow until they are mature enough to perform their functions properly. They are then released into the bloodstream to circulate around the body.

White blood cells

There are two main types of white blood cell: myeloid cells and lymphocytes. These cells work together to fight infection. There are different types of myeloid cells that help to fight off different types of infection. The different myeloid cells are:

• neutrophils
• monocytes
• eosinophils
• basophils.

The myeloid cells, and some lymphocytes, only live for a few days, so the bone marrow is constantly making new cells to replace the old ones. The bone marrow normally makes millions of blood cells every day. When they are mature enough to leave the bone marrow, the white blood cells are released into the bloodstream to circulate around the body.