What is hairy cell leukaemia?

Leukaemia is a type of blood cancer.

If you have any type of blood cancer, it means some of your blood cells are not working properly.

There are different types of blood cell in the body – red blood cells, white blood cells and platelets. They all do different, important jobs.

There are many different types of blood cancer, depending on which blood cells are affected.

In leukaemia, it is often the white blood cells that are affected.

Hairy cell leukaemia is a type of blood cancer that affects cells called B lymphocytes. These are a type of white blood cell. They are part of the immune system and help your body to fight infections.

Your body makes new blood cells all the time, which you need to stay healthy. Blood cells are made inside the bone marrow, which is a soft spongy tissue found in the middle of some bones.

In hairy cell leukaemia, your bone marrow makes abnormal B lymphocytes. They don’t work properly, so they can’t protect you from infection like they should. As they build up, they also stop the production of other healthy blood cells that your body needs.

These abnormal B lymphocytes are called “hairy cells”. They get their name from the fine hair-like strands seen on the surface of the cells under a microscope.

Hairy cell leukaemia is sometimes referred to as “classical” hairy cell leukaemia, as there is also a condition called hairy cell leukaemia-variant. Doctors used to think the two conditions were related, but they are now seen as very different. This information is about classical hairy cell leukaemia.

An estimated 230 people are diagnosed with hairy cell leukaemia each year in the UK.

It is more common in older people, with half of all cases (50%) in people aged 68 or over. A quarter (25%) of cases are in people under 55.

It’s also more common in males than females.

It’s not clear what causes hairy cell leukaemia. Hairy cell leukaemia can happen to anyone, and it’s not because of anything you have done.

There is no clear evidence to suggest that hairy cell leukaemia runs in families.

• Hairy cell leukaemia and family history – People with a close relative with hairy cell leukaemia (a parent, sibling or child) have a slightly increased risk of developing it themselves. But overall the risk is still very low, and most people with a family history never develop hairy cell leukaemia.
• BRAF gene mutation – Recent research has found that the cancer cells in hairy cell leukaemia have a specific mutation of the “BRAF” gene. But this is a mutation that happens when hairy cell leukaemia develops – it’s not a mutation found in healthy cells in the body, so it’s not something that can be passed down to children.