What Is Hairy Cell Leukemia?

Hairy cell leukemia (HCL) is a cancer of the blood that starts in your bone marrow -- the soft tissue inside some of your bones where blood cells are made.

It happens when your bone marrow makes too many white blood cells called B lymphocytes. The cells that cause the cancer look "hairy" under a microscope, which is what gives HCL its name.

It's a rare condition -- only about 1,000 people get it each year in the U.S. Men get it more often than women, and adults get it more often than children.

HCL is a chronic cancer. That means it doesn't go away completely with treatment. But it grows very slowly. With medical care, you can live for a very long time with the disease.


The buildup of leukemia cells in your blood and bone marrow affects how well your blood works in your body. This means you might have symptoms like:

  • Bleeding or bruising caused by a low number of platelets
  • Feeling tired and weak from anemia (low red blood cell count)
  • Frequent fevers
  • Infections from a low white blood cell count
  • Lumps in your neck, underarm, stomach, or groin
  • Shortness of breath
  • Weight loss you can't explain

Often, hairy leukemia cells collect in your spleen, which can make it bigger. This can cause pain or a feeling of fullness in your belly just under your ribs. Sometimes, hairy cells can affect your liver. They can sometimes cause bone pain.

It's also possible to have no signs or symptoms.



Your blood is made up of three kinds of cells: red blood cells, platelets, and white blood cells. Each type has a certain job:

  • Red blood cells carry oxygen to your tissues.
  • White blood cells fight infection in your body.
  • Platelets form blood clots to help you stop bleeding.

All these are made by your bone marrow. They start out as stem cells. Stem cells are like blank slates. Over time, they can become any of the three types of blood cells.

When you have hairy cell leukemia, a change (or mutation) in your genes causes your body to make too many of the white blood cells called B lymphocytes. As a result, fewer of your blood stem cells grow into other types of white blood cells, platelets, or red blood cells.

And the B lymphocytes that crowd out your platelets and red blood cells aren't normal. They can't fight infection like healthy white blood cells do. These are hairy leukemia cells.

Doctors aren't sure why this mutation happens.


To get the right diagnosis, you may need to see a hematologist -- a doctor who specializes in blood and diseases related to it. She can use several tests to find out if you have HCL:

  • Physical tests. If your spleen is larger than normal because of the hairy cell buildup, your doctor may be able to feel it. She'll press on your abdomen just below your ribcage. If that doesn't tell her what she needs to know, you can also have a computerized tomography (CT) scan. Several X-rays are taken from different angles and put together to make a more detailed picture of your spleen. She may also check you for swollen lymph nodes in your abdomen or in other places on your body.
  • Blood tests. Your doctor will take a sample of your blood and send it to a lab for a complete blood count, or CBC. This will tell her if you have lower counts of red blood cells, platelets, and certain types of white blood cells than you should. You can also have a test called a peripheral blood smear. This test looks specifically for hairy leukemia blood cells.
  • Bone marrow biopsy. This test looks for signs of cancer in your bone marrow, blood, and bone. Your doctor will put a hollow needle into your breastbone or hipbone and take out a small piece of bone, some bone marrow, and some blood to look at under a microscope. This is called bone marrow aspiration.




The type of treatment your doctor chooses for you depends on:

  • How many healthy blood cells you have versus hairy leukemia cells in your blood and bone marrow
  • Whether your spleen is larger than normal
  • Whether you have infection in your blood or other signs of leukemia (fevers, sweats, weight loss)
  • How many times you've had HCL come back after treatment

Once your doctor has a better idea of how your HCL is affecting you, he may recommend one or more of these:

  • If your HCL grows slowly and doesn't cause any symptoms, your doctor may decide you don't need treatment right away. He may recommend "watchful waiting" before starting a treatment plan.
  • Chemotherapy: The doctor uses drugs that kill cancer cells or make them grow more slowly. There are two options: cladribine (Leustatin) and pentostatin (Nipent). They both are put into your body through an IV. Most people with HCL who take chemotherapy drugs go into complete or partial remission (when there are no signs of cancer in your blood).
  • Immunotherapy: This uses your own immune system to fight HCL. Two common therapies that do this are interferon and rituximab (Rituxan). The drug moxetumomab (Lumoxiti) is given if other treatments have not helped.
  • Surgery: You might need to have your spleen removed (a splenectomy) if it's painful or if it bursts. This won't cure your HCL, but your blood count may go back to normal.


WebMD Medical Reference Reviewed by Laura J. Martin, MD on November 17, 2018



National Cancer Institute: "Hairy Cell Leukemia."

Leukemia & Lymphoma Society: "Hairy Cell Leukemia," "Hairy Cell Leukemia Facts."

Mayo Clinic: "Hairy Cell Leukemia."

Hairy Cell Leukemia Foundation: "About HCL."

American Cancer Society: "Chemotherapy: What it is, How it helps" and "Treating Hairy Cell Leukemia."

© 2018 WebMD, LLC. All rights reserved.