Hairy cell leukemia is a cancer of the white blood cells. The white blood cells help fight off germs. There are a few different types of white blood cells. The white blood cells involved in hairy cell leukemia are called B cells. B cells are also called B lymphocytes.

In hairy cell leukemia, the body makes too many B cells. The cells don’t look like healthy B cells. Instead, they’ve undergone changes to become leukemia cells. The leukemia cells look “hairy” under a microscope.

Hairy cell leukemia cells keep living when healthy cells would die as part of the natural cell life cycle. The leukemia cells build up in the body and cause symptoms.

Hairy cell leukemia often gets worse slowly. Treatment might not need to start right away. When it’s needed, treatment is usually with chemotherapy.

Scientists found a type of cancer that looks like hairy cell leukemia, but it gets worse much faster. This other type of cancer is called hairy cell leukemia variant. It’s considered a separate type of cancer from hairy cell leukemia, even though it has a similar name.


Hairy cell leukemia might not cause symptoms. Sometimes a health care provider finds it by accident during a blood test for another condition.

When it causes symptoms, hairy cell leukemia might cause:

  • A feeling of fullness in your belly that may make it uncomfortable to eat more than a little at a time
  • Fatigue
  • Easy bruising
  • Recurring infections
  • Weakness
  • Losing weight without trying


It’s not clear what causes hairy cell leukemia.

Hairy cell leukemia begins in the white blood cells. The white blood cells help fight germs in the body. There are a few types of white blood cells. The white blood cells involved in hairy cell leukemia are called B cells.

Hairy cell leukemia happens when B cells develop changes in their DNA. A cell’s DNA contains the instructions that tell a cell what to do. The changes tell the B cells to make a lot more B cells that don’t work right. These cells go on living when healthy cells would die as part of the natural cell life cycle.

The B cells that don’t work right crowd out healthy blood cells in the bone marrow and other organs. This leads to the symptoms and complications of hairy cell leukemia. For example, the extra cells can cause swelling in the spleen, liver and lymph nodes. If there isn’t enough room for healthy blood cells, this can lead to frequent infections, easy bruising and feeling very tired.

Risk factors

The risk of hairy cell leukemia may be higher in:

  • Older adults. Hairy cell leukemia can happen at any age. But most people diagnosed with hairy cell leukemia are in their 50s or 60s. It’s rare in children.
  • Males. Hairy cell leukemia can happen to anyone. But it’s more likely in males.


Hairy cell leukemia often gets worse very slowly. Sometimes it stays stable for many years. For this reason, few complications of the disease occur.

Too few healthy blood cells

If there are too many leukemia cells in the body, they can crowd out the healthy blood cells. That can lead to:

  • Infections. Your body needs healthy white blood cells to fight off germs. If your body can’t make enough healthy white blood cells, you might get more infections.
  • Bleeding. Your body needs healthy platelet cells to control bleeding. If the number of platelets in your blood is low, you might notice that you bruise more easily. You might also have bleeding from the nose or gums.
  • Anemia. Your body needs healthy red blood cells to carry oxygen through your body. Having too few red blood cells is called anemia. Anemia can make you feel very tired.

Increased risk of other cancers

Some studies found that people with hairy cell leukemia have an increased risk of other types of cancer. The other cancers include non-Hodgkin’s lymphoma, Hodgkin’s lymphoma and others. It’s not clear if the other cancers are caused by hairy cell leukemia or by cancer treatments.


Diagnosing hairy cell leukemia usually involves a series of tests, including blood tests and bone marrow tests.

Blood Tests

Your doctor needs to test your blood to help make a diagnosis. Your blood is sent to a lab for a complete blood count (CBC), which shows the number of red cells, white cells and platelets in your blood. If you have hairy cell leukemia, you’ll have lower than normal levels of red cells, platelets and normal white cells. Occasionally, the blood contains many hairy cells, which increases the total white cell count. However, levels of white cells called neutrophils and monocytes are still extremely low.

Bone Marrow Tests

Your doctor or oncologist (cancer specialist) tests your bone marrow. Bone marrow testing involves two steps usually done at the same time in a doctor’s office or a hospital:

  • A bone marrow aspiration to remove a liquid marrow sample
  • A bone marrow biopsy to remove a small amount of bone filled with marrow

Lab Tests to Confirm a Diagnosis

A hematopathologist examines samples of your blood and marrow to confirm a diagnosis. A hematopathologist is a specialist who studies blood cell diseases by looking at samples of blood and marrow cells and other tissues.

Hairy cells can be hard to find in the blood but can often be identified with careful searching. The hematologist stains dried marrow cells under a lighted microscope to identify whether hairy cells are present. The marrow cells often have a characteristic pattern to them. However, a firm diagnosis requires immunophenotyping performed on the blood or marrow cells. Immunophenotyping looks for a characteristic marker (antigen) on the surfaces of lymphocytes to determine if they form a certain pattern that indicates hairy cell leukemia. Flow cytometry is one type of test used for immunophenotyping.

Imaging Studies

You may need to undergo imaging studies to determine the extent of your disease. Your doctor may order an ultrasound to see the precise size of your spleen. Once your therapy begins, you may need to undergo follow-up imaging tests so your doctor can see whether the size of your spleen, liver or lymph nodes have decreased in response to treatment.

Only about 5 percent to 10 percent of hairy cell leukemia patients have enlarged lymph nodes (lymphadenopathy) when they’re diagnosed. People whose disease is more advanced or who have a relapse (your cancer returns after remission, the period of no evidence of the disease) may have enlarged lymph nodes in their stomach area (abdominal lymphadenopathy). Your doctor may check your lymph nodes with a computed tomography (CT) scan during the course of managing your disease.


It’s important that your doctor is experienced in treating patients with hairy cell leukemia or works in consultation with a hairy cell leukemia specialist. This type of specialist is usually called a hematologist oncologist.

Types of Hairy Cell Leukemia Treatment

For many people with hairy cell leukemia, starting treatment helps them focus on moving ahead and looking forward to their disease’s remission.

Several types of approaches and treatment are used for adults with hairy cell leukemia, some at different stages:

  • Watch and wait
  • Chemotherapy
  • Splenectomy
  • Clinical trial

Finding the Best Treatment Approach

The goal of hairy cell leukemia treatment is to achieve a complete remission (when there are no signs of the disease). A complete remission means that:

  • Hairy cells can’t be identified in the blood and bone marrow
  • The liver, spleen and lymph nodes are a normal size
  • Blood cell and marrow cell counts have returned to normal

Most people with hairy cell leukemia receive treatment immediately after they’re diagnosed or at some point during the disease’s course. A small percentage of patients may not need immediate treatment. Instead, they’ll be monitored until signs and symptoms of the disease appear.

As you develop a treatment plan with your doctor, be sure to discuss:

  • The results you can expect from treatment
  • Potential side effects, including long-term and late effects
  • The possibility of participating in a clinical trial, where you’ll have access to advanced medical treatment that may be more beneficial to you than standard treatment

You may find it helpful to bring a loved one with you to your doctor’s visits for support and to take notes and ask follow-up questions. You can also record your conversations with your doctor and listen more closely when you get home.

Other Treatment Considerations

  • If you’re age 60 or older, your treatment may vary from standard approaches. For instance, your body may not be able to tolerate toxic chemotherapy drugs or you may have other ailments that are more common as we age. These factors, among others, may make choosing a treatment more complicated.
  • If your cancer has returned (relapsed) or it’s still present after you finish standard therapy (refractory leukemia), you might have a different treatment approach than the first time around.

Common Side Effects

Chemotherapy drugs are the main culprits when it comes to causing unwanted side effects. These drugs can kill cancer cells, but they damage normal cells, too. The lining of the mouth, throat, stomach and intestines are particularly vulnerable to damage.

The side effects you may experience depend on:

  • The intensity of chemotherapy
  • The drugs used during therapy
  • Your overall health and whether you have any chronic health conditions like diabetes or kidney disease

About half of all patients treated with the chemotherapy drug cladribine (Leustatin®) get fevers of about 100° F during or immediately after treatment. The fevers aren’t associated with infection; they’re caused by a drop in hairy cells in the body. The fevers usually go away in three to 10 days.

Patients may also feel tired during the first few weeks of treatment because of low blood cell counts. But eventually the levels improve and often return to normal.

The following side effects are also common. 

  • Infections
  • Hair loss
  • Nausea and vomiting
  • Diarrhea
  • Constipation
  • Mouth sores
  • Aches and pains
  • Low blood pressure
  • Low levels of red cells, white cells and platelets in the blood
  • Anemia (caused by a low red cell count)
  • Graft vs. host disease (if you’ve undergone allogeneic stem cell transplantation)

Long-Term and Late Effects

For some patients, side effects may last well after treatment is finished. To read more about lingering side effects.

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