Leukaemia

Leukaemia is a cancer which starts in blood-forming tissue, usually the bone marrow. It leads to the over-production of abnormal white blood cells, the part of the immune system which defends the body against infection.

Blood cells are formed in the bone marrow, the spongy tissue found inside the bones. Blood-forming stem cells divide to produce either more stem cells or immature cells that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

A myeloid stem cell becomes one of three types of mature blood cells:

• Red blood cells that carry oxygen to all tissues of the body.
• Platelets that form blood clots to stop bleeding.
• Granulocytes (white blood cells) that fight infection and disease.

A lymphoid stem cell becomes a lymphoblast cell and then one of three types of lymphocytes (white blood cells):

• B lymphocytes that make antibodies to help fight infection.
• T lymphocytes that help B lymphocytes make the antibodies that help fight infection.
• Natural killer cells that attack cancer cells and viruses.

Leukaemia affects white blood cells and can be classified by the type of white cell affected (myeloid or lymphatic) and by the way the disease progresses (acute or chronic). Acute and chronic do not refer to how serious the disease is but to how rapidly it progresses.

Signs and symptoms

Signs and symptoms of leukaemia (and blood cancers generally are notoriously vague and non-specific). There are no specific signs or symptoms of any type of leukaemia which would allow a doctor to make a diagnosis without laboratory tests.

In all types of leukaemia, symptoms are more commonly caused by lack of normal blood cells than by the presence of abnormal white cells. As the bone marrow becomes full of leukaemia cells, it is unable to produce the large numbers of normal blood cells which the body needs. This leads to:

• Anaemia – due to lack of red blood cells
• Weakness, tiredness, shortness of breath, light-headedness, palpitations
• Infections – due to lack of normal white blood cells
• Infections are more frequent, more severe and last longer
• Fever, malaise (general feeling of illness) and sweats
• Purpura (small bruises in skin), heavy periods, nosebleeds, bleeding gums
• Bleeding and bruising – due to lack of platelets

There are some symptoms that are only seen in certain patients or forms of leukaemia. For example, young children with ALL may complain of pain in bones or joints and, in some types of AML, the gums may be swollen by leukaemia cells in the tissues.

In lymphoid malignancies, lymph nodes (glands) may be swollen. In some forms of the leukaemia the liver may be enlarged (hepatomegaly) or the spleen (an organ of the immune system found just under the ribs on the left hand side) may be enlarged (splenomegaly).

What causes leukaemia?

In most cases of leukaemia there is no obvious cause. However, it is important to understand that:

• Leukaemia is not a condition which can be caught from someone else (contagious)
• Leukaemia is not passed on from a parent to a child (inherited)

Risk factors:

• Age - most forms of leukaemia are more common in older people. The main exception to this is ALL in which peak incidence is in children
• Gender - leukaemias are generally more common in males
• Genetics - although leukaemia is not an inherited disease, there is a slightly higher chance that close relatives of patients may develop some forms of leukaemia. The risk is still very small and there is no cause for anxiety or for screening tests
• Chemical exposure - being exposed to some chemicals and high levels of radiation may increase the chance of developing leukaemia. These factors account for only a very small proportion of all cases
• Some forms of leukaemia are seen more commonly in people who have other bone marrow disorders. The most common disorders which behave in this way are myelodysplastic syndrome (MDS) and the myeloproliferative neoplasms (MPN)
  

Types of leukaemia

There are four main types of leukaemia:

• Acute myeloid leukaemia (AML) - Rapidly developing, affects myeloid cells (granulocytes)
• Chronic myeloid leukaemia (CML) - Slowly developing, affects myeloid cells (granulocytes)
• Acute lymphoblastic leukaemia (ALL) - Rapidly developing, affects lymphocytes
• Chronic lymphocytic leukaemia (CLL) - Slowly developing, affects lymphocytes

Acute leukaemia progresses rapidly, unless effectively treated but it can often be cured with standard treatments, such as bone marrow transplants, especially in younger and/or fitter patients, 

Chronic leukaemia progresses slowly but, although it can be treated and managed, it is not usually possible to cure chronic leukaemia with standard treatments.