Leukaemia is a cancer of the white blood cells (WBCs) originating in the bone marrow. Over 7000 people are diagnosed with leukaemia annually in the UK, making it the 10th most common cancer in men and 9th in women. While exposure to radiation, benzene, and some anticancer drugs have been shown to increase the risk of developing leukaemia, and a few cases are associated with genetic disorders or rare viral infections, the cause of most leukaemias is not known.
What is it?
Leukaemia is a bone marrow disorder that arises when one abnormal white blood cell begins to continuously replicate itself. Except in the case of chronic myeloid leukaemia (CML), leukaemic cells do not function normally, i.e. they do not fight infection as they should and they do not die at the same rate as other WBCs. As they accumulate, the cells inhibit the production of the other normal blood cells in the marrow, leading to anaemia, bleeding, and recurrent infections. Over time, the leukaemic cells spread through the bloodstream where they continue to divide, sometimes forming tumours and damaging organs such as the kidney and liver. Since the spleen is responsible for filtering the blood and destroying old cells, it may become enlarged and swollen with the abnormal cells, as can the liver and lymph nodes. If the cells reach the central nervous system and build up in the cerebrospinal fluid that surrounds the brain and spinal column, they can cause headaches and seizures.
The bone marrow, located in the soft centre of the body's larger bones, produces precursors (immature versions) of red blood cells, platelets, and various kinds of white blood cells. The most immature recognisable precursor is called a blast cell. Most of these blood cells mature in the bone marrow before being released into the bloodstream. The WBCs created are grouped into two main categories: lymphoid and myeloid. Myeloid cells (which include neutrophils, basophils, eosinophils, (collectively known as granulocytes due to granules visible inside them) and monocytes) circulate in the blood, killing and digesting bacteria. Lymphocytes, which are found in both the blood stream and the lymphatic system, coordinate the immune response and produce antibodies. Leukaemia arises from any one of these white blood cells. It is categorised both by the type of WBC involved and by how quickly it progresses. Although expanded classifications of the disease exist, the main types of leukaemia can be grouped as:
- Acute lymphocytic leukaemia (ALL). Affects approximately 200 adults each year in the UK. This is a rapidly developing disease that is characterized by large numbers of immature lymphocytes (lymphoblasts). It is the most common type of leukaemia found in children, although it affects both children and adults (usually adults age 65 and older).
- Chronic lymphocytic leukaemia (CLL). This disease progresses more slowly and is characterized by an excess of mature lymphocytes. It tends to be found in those over the age of 55 or 60 and is almost never found in those under 40
- Acute myeloid leukaemia (AML). Affecting people of all ages, although it becomes increasingly common with age and is predominantly found in those over 60, this disease is characterized by production of large numbers of immature granulocyte myeloid cells (myeloblasts) that replace other normal cells in the marrow.
- Chronic myeloid (or granulocytic) leukaemia (CML or CGL). Chronic myeloid leukaemia affects approximately 700 people (mostly adults) in the UK each year. It is an acquired condition that begins in an immature stem cell in the bone marrow when pieces from two chromosomes (9 and 22) break off and switch places (translocation). This results in an altered, fused gene (bcr-abl) on chromosome 22 that produces an abnormal which affects cell growth regulation. This leads to an overproduction of myeloid white blood cells, and the presence of both mature and immature cells in the bloodstream.