Hairy cell leukaemia is a rare type of long-term (chronic) leukaemia.

The condition gets its name from the fine, hair-like strands that develop around the outside of the cancerous cells and are visible under a microscope.

It's not known what causes hairy cell leukaemia.

Leukaemia

Leukaemia is cancer of the white blood cells.

All the body's blood cells, including red and white blood cells and platelets, are produced by bone marrow. Bone marrow is a spongy tissue found inside the bones. It also produces special cells called stem cells.

In leukaemia, the cancer begins in the stem cells and causes them to produce more white blood cells than are needed. Over time, the build-up of cancerous white blood cells disrupts the normal balance of cells in the blood.

This means your body doesn't have enough red blood cells, which carry oxygen around the body, or platelets, which help stop bleeding. This can lead to the symptoms of anaemia, such as tiredness, shortness of breath and feeling faint, as well as increasing the risk of excessive bleeding.

Also, as the white blood cells aren't properly developed, they're less effective at fighting bacteria and viruses, making you more vulnerable to infection.

Hairy cell leukaemia

The symptoms of hairy cell leukaemia develop slowly and are similar to those of other types of leukaemia. They include:

• weight loss 
• pale skin
• weakness, tiredness and breathlessness (due a lack of red blood cells)
• frequent infections (due to a lack of infection-fighting white blood cells)
• bleeding or bruising easily
• pain or swelling in your abdomen (tummy) (see below)

The abnormal white blood cells can accumulate in your spleen, causing it to increase in size. The spleen is an organ in the upper left side of your abdomen, behind your stomach and ribs.

If your spleen is enlarged, it's likely you'll have a painful lump on the left side of your abdomen. If this is the case, you should visit your GP so the lump can be examined.

An enlarged spleen may remove normal blood cells from your bloodstream. This can lead to a further reduction in the number of normal red and white blood cells and platelets in your blood.

Diagnosis

If your GP suspects leukaemia, they may refer you to a haematologist (a specialist in blood disorders).

The haematologist will carry out blood tests to determine how many different types of blood cells there are in your blood sample. This is known as a full blood count (FBC) and will indicate the number of abnormal white blood cells you have.

If you have hairy cell leukaemia, it's likely your red blood cell and platelet counts will be low.

A bone marrow sample may also be taken which will give the haematologist more detailed information about your condition.

An ultrasound scan or a computerised tomography (CT) scan may be needed to examine your spleen.

Treatment

As hairy cell leukaemia develops slowly, immediate treatment may not be needed. You'll have regular blood tests to monitor your condition.

Treatment may be recommended if the number of abnormal white blood cells increases or if you develop symptoms.

A number of different treatments are available for hairy cell leukaemia. Chemotherapy is the main treatment and it's usually effective at destroying the cancerous cells.

Other treatments are sometimes used in combination with chemotherapy.

Rituximab is a type of medication known as a monoclonal antibody. It seeks out a protein found on leukaemia cells and attaches itself to it. The immune system then targets and kills the cells.

Interferon is another medicine that can be used to treat hairy cell leukaemia. It can strengthen your immune system and help fight cancer. This type of treatment, known as immunotherapy, may be recommended if you can't have chemotherapy or rituximab, or they're no longer working.

Surgery to remove the spleen is rarely used as a treatment for hairy cell leukaemia. However, removal of your spleen may be recommended if:

• it's enlarged and is causing pain or discomfort
• it's destroying large numbers of red blood cells or platelets
• it hasn't shrunk after chemotherapy

The Cancer Research UK website has more information about the types of treatment for hairy cell leukaemia.

Outlook

As with most types of cancer, the outlook for hairy cell leukaemia will depend on how far the condition has advanced at the time of diagnosis and how well it responds to treatment.

As hairy cell leukaemia is a rare type of cancer, it's difficult to accurately predict how it will affect individuals in the long-term. 

However, according to Cancer Research UK, at least 96 out of 100 people diagnosed with hairy cell leukaemia (96%) will live at least 10 years after being diagnosed.