Hairy cell leukemia is a rare, slow-growing cancer of the blood in which your bone marrow makes too many B cells (lymphocytes), a type of white blood cell that fights infection.

These excess B cells are abnormal and look "hairy" under a microscope. As the number of leukemia cells increases, fewer healthy white blood cells, red blood cells and platelets are produced.

Hairy cell leukemia affects more men than women, and it occurs most commonly in middle-aged or older adults.

Hairy cell leukemia is considered a chronic disease because it may never completely disappear, although treatment can lead to a remission for years.


Some people have no signs or symptoms of hairy cell leukemia, but a blood test for another disease or condition may inadvertently reveal hairy cell leukemia.

Other times people with hairy cell leukemia experience signs and symptoms common to a number of diseases and conditions, such as:

  • A feeling of fullness in your abdomen that may make it uncomfortable to eat more than a little at a time
  • Fatigue
  • Easy bruising
  • Recurring infections
  • Weakness
  • Weight loss

When to see a doctor

Make an appointment with your doctor if you have any persistent signs and symptoms that worry you.


It's not clear what causes hairy cell leukemia.

Doctors know that cancer occurs when cells develop errors (mutations) in their DNA. In the case of hairy cell leukemia, mutations in the DNA cause your bone marrow stem cells to create too many white blood cells that don't work properly. Doctors don't know what causes the DNA mutations that lead to hairy cell leukemia.

Risk factors

Certain factors may increase your risk of developing hairy cell leukemia. Not all research studies agree on what factors increase your risk of the disease.

Some research indicates that your risk of hairy cell leukemia increases based on your:

  • Exposure to radiation. People exposed to radiation, such as those who work around X-ray machines and do not wear adequate protective equipment or those who received radiation treatment for cancer, may have a higher risk of developing hairy cell leukemia, but the evidence is inconclusive.
  • Exposure to chemicals. There are conflicting studies on the role of industrial and agricultural chemicals in hairy cell leukemia development.


Hairy cell leukemia progresses very slowly and sometimes remains stable for many years. For this reason, few complications of the disease occur.

Untreated hairy cell leukemia that progresses may crowd out healthy blood cells in the bone marrow, leading to serious complications, such as:

  • Infections. Reduced numbers of healthy white blood cells put you at risk of infections that your body might otherwise fight off.
  • Bleeding. Low platelet counts make it hard for your body to stop bleeding once it starts. If you have a mildly low platelet count, you might notice that you bruise more easily. Very low platelet counts can cause spontaneous bleeding from the nose or gums.
  • Anemia. A low red blood cell count means fewer cells are available to carry oxygen throughout your body. This is called anemia. Anemia causes fatigue.

Increased risk of second cancers

Some studies have found that people with hairy cell leukemia may have an increased risk of developing a second type of cancer. It isn't clear whether this risk is due to hairy cell leukemia's effect on the body or if the risk comes from the medications used to treat hairy cell leukemia.

Second cancers found in people treated for hairy cell leukemia include non-Hodgkin's lymphoma, among others.

March 26, 2020
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