Hairy Cell Leukemia

April 19, 2024 
This page was reviewed under our medical and editorial policy by Guido Marcucci, M.D., Chair, Department of Hematologic Malignancies Translational Science, City of Hope Duarte

Hairy cell leukemia, a chronic form of adult leukemia, is rare. About 2% of adults have this type of leukemia. Approximately 1,200 to 1,300 new cases a year are diagnosed in the United States. Though treatment may be needed for this slow-growing cancer, people may live for many years after treatment.

What Is Hairy Cell Leukemia?

Hairy cell leukemia (HCL) is marked by abnormal B lymphocytes, a type of white blood cell found in the bone marrow, spleen and blood. Under a microscope, the abnormal cells appear to be covered in thin strands that look like hair, thus the name. This type of leukemia typically progresses slowly, but it does not always respond to treatment, and once treated, it may recur.

Hairy Cell Leukemia Stages

Unlike other types of cancer, hairy cell leukemia does not have a standard staging system. Rather, treatment decisions are based on the symptoms the patient is having and how much the blood cell counts change.

Hairy Cell Leukemia Symptoms

Patients with hairy cell leukemia may have:

• Frequent infections
• Weakness or weariness from anemia
• Bruising or bleeding easily
• Shortness of breath
• A sensation of pain or fullness below the ribs
• Painless lumps in the neck, underarm, stomach or groin

Even though this type of leukemia affects white cells, patients do not typically develop enlarged lymph nodes. However, the spleen is typically enlarged.

What Causes Hairy Cell Leukemia?

The cause of hairy cell leukemia is not known, but how it develops is known.

All blood cells (white, red and platelets) are formed from stem cells. Sometimes, the genetic material (DNA) is damaged as stem cells develop. This is known as an acquired mutation. In hairy cell leukemia, the abnormal change occurs in B lymphocytes, which are white blood cells that normally produce antibodies to help fight foreign invaders. Hairy cells overproduce and crowd out normal blood cells. When the counts of white cells, red cells and platelets are low, it is called pancytopenia.

Men are four times more likely than women to be affected by hairy cell leukemia. Half of those who are diagnosed are 55 or older.

Hairy Cell Leukemia Diagnosis and Tests

A number of blood tests and bone marrow tests are used to diagnose HCL.

Blood tests include a complete blood count (CBC). A CBC counts the number of red cells, white cells and platelets in a blood sample. Hairy cell leukemia may increase the overall white count, but levels of the healthy white cells, red cells and platelets are likely to be extremely low.

Bone marrow tests include:

• Aspiration, in which a sample of liquid bone marrow is obtained
• Biopsy, in which a small amount of bone marrow is removed
• Examination by a hematopathologist, a pathologist who specialize in blood diseases, who checks these samples under a microscope for hairy cells
• Immunophenotyping, which looks for a characteristic marker (antigen) on the surface of white blood cells, typically with flow cytometry

Imaging tests may also be needed. These include:

• An ultrasound to measure the size of the spleen
• A computed tomography (CT) scan to look for enlarged lymph nodes, especially in the abdomen

Hairy Cell Leukemia Treatment

Not everyone diagnosed with hairy cell leukemia needs treatment right away. A small number of patients may be able to wait until monitoring shows that the disease is progressing.

For those who need immediate treatment, different approaches may be used. These may be based on the patient’s age and the degree of abnormality in the blood count. Treatments may include:

• Chemotherapy using cladribine (2-CdA) or pentostatin
• Splenectomy, or removal of the spleen, though this is less common today because chemotherapy agents are highly successful
• Clinical trials
• Immunotherapy, which helps the immune system move toward diseased cells, may be possible if the cancer does not respond to chemotherapy.
• Targeted therapy, in which drugs are used to target specific proteins in or on cancer cells, is sometimes used.

Hairy Cell Leukemia Survival Rate

Hairy cell leukemia acts like a chronic rather than acute leukemia. It tends to grow slowly, and once treated, most patients go into remission. Sometimes, no hairy cells are seen over the long term.

After treatment, most people may expect to live 10 years or more, according to the U.S. National Library of Medicine. Many people will go on to have a normal life expectancy.