Hairy cell leukemia is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell).

Hairy cell leukemia is a cancer of the blood and bone marrow. This rare type of leukemia gets worse slowly or does not get worse at all. The disease is called hairy cell leukemia because the leukemia cells look "hairy" when viewed under a microscope.

Anatomy of the bone. The bone is made up of compact bone, spongy bone, and bone marrow. Compact bone makes up the outer layer of the bone. Spongy bone is found mostly at the ends of bones and contains red marrow. Bone marrow is found in the center of most bones and has many blood vessels. There are two types of bone marrow: red and yellow. Red marrow contains blood stem cells that can become red blood cells, white blood cells, or platelets. Yellow marrow is made mostly of fat.

Leukemia may affect red blood cells, white blood cells, and platelets.

Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

A myeloid stem cell becomes one of three types of mature blood cells:

• Red blood cells that carry oxygen and other substances to all tissues of the body.
• White blood cells that fight infection and disease.
• Platelets that form blood clots to stop bleeding.

A lymphoid stem cell becomes a lymphoblast cell and then into one of three types of lymphocytes (white blood cells):

• B lymphocytes that make antibodies to help fight infection.
• T lymphocytes that help B lymphocytes make antibodies to help fight infection.
• Natural killer cells that attack cancer cells and viruses.

Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.

In hairy cell leukemia, too many blood stem cells become lymphocytes. These lymphocytes are abnormal and do not become healthy white blood cells. They are also called leukemia cells. The leukemia cells can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells, and platelets. This may cause infection, anemia, and easy bleeding. Some of the leukemia cells may collect in the spleen and cause it to swell.

This summary is about hairy cell leukemia. See the following PDQ summaries for information about other types of leukemia:

• Adult Acute Lymphoblastic Leukemia Treatment.
• Childhood Acute Lymphoblastic Leukemia Treatment.
• Chronic Lymphocytic Leukemia Treatment.
• Adult Acute Myeloid Leukemia Treatment.
• Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies Treatment.
• Chronic Myelogenous Leukemia Treatment.

Gender and age may affect the risk of hairy cell leukemia.

Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer. Talk with your doctor if you think you may be at risk. The cause of hairy cell leukemia is unknown. It occurs more often in older men.

Signs and symptoms of hairy cell leukemia include infections, tiredness, and pain below the ribs.

These and other signs and symptoms may be caused by hairy cell leukemia or by other conditions. Check with your doctor if you have any of the following:

• Weakness or feeling tired.
• Fever or frequent infections.
• Easy bruising or bleeding.
• Shortness of breath.
• Weight loss for no known reason.
• Pain or a feeling of fullness below the ribs.
• Painless lumps in the neck, underarm, stomach, or groin.

Tests that examine the blood and bone marrow are used to detect (find) and diagnose hairy cell leukemia.

The following tests and procedures may be used:

• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as a swollen spleen, lumps, or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
• Complete blood count (CBC): A procedure in which a sample of blood is drawn and checked for the following:

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  The number of red blood cells, white blood cells, and platelets.

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  The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.

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  The portion of the sample made up of red blood cells.

  

  Complete blood count (CBC). Blood is collected by inserting a needle into a vein and allowing the blood to flow into a tube. The blood sample is sent to the laboratory and the red blood cells, white blood cells, and platelets are counted. The CBC is used to test for, diagnose, and monitor many different conditions.

• Peripheral blood smear: A procedure in which a sample of blood is checked for cells that look "hairy," the number and kinds of white blood cells, the number of platelets, and changes in the shape of blood cells.
• Blood chemistry studies: A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.
• Bone marrow aspiration and biopsy: The removal of bone marrow, blood, and a small piece of bone by inserting a hollow needle into the hipbone or breastbone. A pathologist views the bone marrow, blood, and bone under a microscope to look for signs of cancer.

  

  Bone marrow aspiration and biopsy. After a small area of skin is numbed, a bone marrow needle is inserted into the patient’s hip bone. Samples of blood, bone, and bone marrow are removed for examination under a microscope.

• Immunophenotyping: A laboratory test in which the antigens or markers on the surface of a blood or bone marrow cell are checked to see what type of cell it is. This test is done to diagnose the specific type of leukemia by comparing the cancer cells to normal cells of the immune system.
• Flow cytometry: A laboratory test that measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of cells, such as size, shape, and the presence of tumor markers on the cell surface. The cells are stained with a light-sensitive dye, placed in a fluid, and passed in a stream before a laser or other type of light. The measurements are based on how the light-sensitive dye reacts to the light.
• Cytogenetic analysis: A laboratory test in which cells in a sample of tissue are viewed under a microscope to look for certain changes in the chromosomes.
• Gene mutation test: A laboratory test done on a bone marrow or blood sample to check for mutations in the BRAF gene. A BRAF gene mutation is often found in patients with hairy cell leukemia.
• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. A CT scan of the abdomen may be done to check for swollen lymph nodes or a swollen spleen.

Certain factors affect treatment options and prognosis (chance of recovery).

The treatment options may depend on the following:

• The number of hairy (leukemia) cells and healthy blood cells in the blood and bone marrow.
• Whether the spleen is swollen.
• Whether there are signs or symptoms of leukemia, such as infection.
• Whether the leukemia has recurred (come back) after previous treatment.

The prognosis (chance of recovery) depends on the following:

• Whether the hairy cell leukemia does not grow or grows so slowly it does not need treatment.
• Whether the hairy cell leukemia responds to treatment.

Treatment often results in a long-lasting remission (a period during which some or all of the signs and symptoms of the leukemia are gone). If the leukemia returns after it has been in remission, retreatment often causes another remission.

There is no standard staging system for hairy cell leukemia.

Staging is the process used to find out how far the cancer has spread. Groups are used in place of stages for hairy cell leukemia. The disease is grouped as untreated, progressive, or refractory.

The hairy cell leukemia is newly diagnosed and has not been treated except to relieve signs or symptoms such as weight loss and infections. In untreated hairy cell leukemia, some or all of the following conditions occur:

• Hairy (leukemia) cells are found in the blood and bone marrow.
• The number of red blood cells, white blood cells, or platelets may be lower than normal.
• The spleen may be larger than normal.

In progressive hairy cell leukemia, the leukemia has been treated with either chemotherapy or splenectomy (removal of the spleen) and one or both of the following conditions occur:

• There is an increase in the number of hairy cells in the blood or bone marrow.
• The number of red blood cells, white blood cells, or platelets in the blood is lower than normal.

There are different types of treatment for patients with hairy cell leukemia.

Different types of treatment are available for patients with hairy cell leukemia. Some treatments are standard (the currently used treatment), and some are being tested in clinical trials. A treatment clinical trial is a research study meant to help improve current treatments or obtain information on new treatments for patients with cancer. When clinical trials show that a new treatment is better than the standard treatment, the new treatment may become the standard treatment. Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.

Five types of standard treatment are used:

New types of treatment are being tested in clinical trials.

Information about clinical trials is available from the NCI website.

Patients may want to think about taking part in a clinical trial.

For some patients, taking part in a clinical trial may be the best treatment choice. Clinical trials are part of the cancer research process. Clinical trials are done to find out if new cancer treatments are safe and effective or better than the standard treatment.

Many of today's standard treatments for cancer are based on earlier clinical trials. Patients who take part in a clinical trial may receive the standard treatment or be among the first to receive a new treatment.

Patients who take part in clinical trials also help improve the way cancer will be treated in the future. Even when clinical trials do not lead to effective new treatments, they often answer important questions and help move research forward.

Patients can enter clinical trials before, during, or after starting their cancer treatment.

Some clinical trials only include patients who have not yet received treatment. Other trials test treatments for patients whose cancer has not gotten better. There are also clinical trials that test new ways to stop cancer from recurring (coming back) or reduce the side effects of cancer treatment.

Clinical trials are taking place in many parts of the country. Information about clinical trials supported by NCI can be found on NCI’s clinical trials search webpage. Clinical trials supported by other organizations can be found on the ClinicalTrials.gov website.

Follow-up tests may be needed.

Some of the tests that were done to diagnose the cancer or to find out the stage of the cancer may be repeated. Some tests will be repeated in order to see how well the treatment is working. Decisions about whether to continue, change, or stop treatment may be based on the results of these tests.

Some of the tests will continue to be done from time to time after treatment has ended. The results of these tests can show if your condition has changed or if the cancer has recurred (come back). These tests are sometimes called follow-up tests or check-ups.

Untreated Hairy Cell Leukemia

If the patient's blood cell counts are not too low and there are no signs or symptoms, treatment may not be needed and the patient is carefully watched for changes in his or her condition. If blood cell counts become too low or if signs or symptoms appear, initial treatment may include the following:

• Chemotherapy.
• Splenectomy.

Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.

Progressive Hairy Cell Leukemia

Treatment for progressive hairy cell leukemia may include the following:

• Chemotherapy.
• Biologic therapy.
• Splenectomy.
• A clinical trial of chemotherapy and targeted therapy with a monoclonal antibody (rituximab).

Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.

Relapsed or Refractory Hairy Cell Leukemia

Treatment of relapsed or refractory hairy cell leukemia may include the following:

• Chemotherapy.
• Biologic therapy.
• Targeted therapy with a monoclonal antibody (rituximab).
• High-dose chemotherapy.
• A clinical trial of a new biologic therapy.
• A clinical trial of a new targeted therapy.
• A clinical trial of chemotherapy and targeted therapy with a monoclonal antibody (rituximab).

Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.

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