What is hairy cell leukaemia?

Hairy cell leukaemia (HCL) is a rare type of chronic leukaemia. It develops slowly from white cells called B lymphocytes. Doctors look at the cells under a microscope. The cells have hair-like outgrowths on their surfaces. This is where the name hairy cell comes from.

Hairy cell leukaemia usually develops slowly. It can be kept under control for many years with treatment. 

You might hear hairy cell leukaemia called 'classic' or 'classical' hairy cell leukaemia. This is because there's another type of leukaemia called hairy cell leukaemia variant (HCL-V).  Doctors used to think HCL-V was a rare type of hairy cell leukaemia. But they now consider it to be a different condition.

What is leukaemia?

Leukaemia is a blood cancer. Your bone marrow makes blood cells. The bone marrow is the soft inner part of some of your bones.

In most types of leukaemia, abnormal white blood cells are made in the bone marrow. These cells can get into the bloodstream and circulate around the body. They do not develop properly and so do not work normally. For example, they don't give you the protection from infection that they should. There are too many of these abnormal white blood cells. They might stop the bone marrow producing enough healthy blood cells.

They can also build up in the lymph nodes and spleen and cause swelling. 

There are different types of leukaemia. They are divided into two main groups:

• acute leukaemia

• chronic leukaemia

Acute and chronic leukaemia

Acute leukaemias tend to develop quickly and get rapidly worse if they are not treated.

There are 2 main types of acute leukaemia:

• acute myeloid leukaemia (AML) 
• acute lymphoblastic leukaemia (ALL)

Chronic leukaemias develop slowly and tend to get worse slowly, over a long time. 

In chronic leukaemia the white blood cells are almost fully developed. But they are not completely normal. They still work, but not as well as they should do at fighting infection. Your body makes too many of these abnormal white blood cells. 

There are 3 main types of chronic leukaemia:

• chronic lymphocytic leukaemia (CLL)
• chronic myeloid leukaemia (CML)
• hairy cell leukaemia

The blood and blood cells

To understand the effects of any type of leukaemia it helps to know more about blood cells. 

How you make blood cells

Your body makes blood cells in the bone marrow. The bone marrow is the soft inner part of your bones. You make blood cells in a controlled way, as your body needs them.

All blood cells start as the same type of cell, called a stem cell. The stem cells then develop into:

• myeloid stem cells become white blood cells called monocytes and neutrophils (granulocyte), red blood cells and platelets

• lymphoid stem cells, which become white blood cells called lymphocytes

The diagram below helps to explain this.

The type of chronic leukaemia you have tells you which type of white blood cell has become cancerous. In hairy cell leukaemia, it is the white cells called B lymphocytes that become cancerous. 

White blood cells (leucocytes)

There are several different types of white cells in the blood. There are more of some types than others. They are an important part of the immune system, helping the body to fight infection. These blood cells can be made very quickly and generally have a short life. Some only live for a few hours, others for a few days.

Red blood cells (erythrocytes)

Red blood cells carry oxygen from the lungs around the body to the tissues. They give the blood its red colour.

Platelets (thrombocytes)

Platelets are very important in blood clotting. They clump together to form a plug if bleeding occurs. Then they release other chemicals that help the blood to clot and the blood vessel to be repaired.

How leukaemia can affect you

Leukaemia can affect your blood and other areas of your body.

White blood cells

White blood cells help fight infection. If your body makes a lot of abnormal white blood cells, they can prevent normal healthy cells from developing. So you are more likely to get infections and may find it difficult to get rid of them.

Red blood cells and platelets

Too many white blood cells can overcrowd the bone marrow. So there isn't enough space to make other types of blood cells. This can cause a lower than normal number of red blood cells and platelets.

Having too few red blood cells is called anaemia. It can cause you to feel tired and breathless.

Platelets are blood cells that help the blood to clot. If you don’t have enough platelets you can have bleeding problems such as nosebleeds and bruising.

Other parts of your body

Abnormal white blood cells can build up in parts of your body such as the spleen, lymph nodes and liver making them bigger.

This can make your tummy (abdomen) swell and feel uncomfortable. The leukaemia cells can also spread to the brain in some people. 

Other types of chronic leukaemia

The two most common types of chronic leukaemia are:

• chronic myeloid leukaemia (CML)
• chronic lymphocytic leukaemia (CLL)

The difference is the type of white blood cell that has become cancerous.

Hairy cell leukaemia variant (HCL-V) is a separate type of leukaemia. It is different to the typical or classic hairy cell leukaemia.

Chronic myeloid leukaemia (CML)

In CML, the abnormal cells develop from the myeloid blood stem cells. So the cancerous white blood cells are myelocytes. These cells are sometimes called granulocytes.

Chronic lymphocytic leukaemia (CLL)

In CLL the abnormal cells develop from the lymphoid blood stem cells. The cancerous white blood cells are B lymphocytes, also called B cells. 

Hairy cell leukaemia variant (HCL-V)

Doctors used to think HCL-V was a rare type of hairy cell leukaemia. But they now consider it to be a completely different condition.

HCL-V and classic hairy cell leukaemia are both chronic leukaemias. They develop slowly from cells called B lymphocytes. 

HCL-V cells are usually smaller than classic hairy leukaemia cells. They have different genetic material in the cells. And they respond differently to treatment.

How common is hairy cell leukaemia?

Hairy cell leukaemia is very rare. It is estimated that around 230 people are diagnosed with hairy cell leukaemia in the UK each year. It is more common in men than women.