• Hairy cell leukemia is a rare type of chronic leukemia that affects bone marrow and the spleen.
• Hairy cells are named for their fine protrusions that look like hair.
• Symptoms of hairy cell leukemia can be subtle and similar to those of other conditions.
• The overproduction of hairy cells compromises the production and function of blood cells.

Hairy cell leukemia (HCL) is a rare form of chronic leukemia. HCL is a type of leukemia that originates in a person’s bone marrow, and also commonly affects the spleen. In HCL, the bone marrow overproduces lymphocytes that impact the other blood cells. B lymphocytes, or B cells, are white blood cells that help fight infection. When someone has hairy cell leukemia, however, B cells don’t fight infection as well as they should.

Hairy cell leukemia cells are called “hairy cell” because of how the cancer cells look when viewed under a microscope. The cells have fine fragments protruding from their surfaces, mimicking the appearance of hair.

Hairy cell leukemia makes up between 1 percent and 2 percent of adult leukemia diagnoses. About 6,000 persons in the United States have HCL. Approximately 600 to 800 new cases of HCL are diagnosed each year in the U.S. HCL may occur in individuals ages 20 to 80, but it is most commonly seen in men over 50 years old. Men are four times as likely to get hairy cell leukemia as women.

Read more about other types of leukemia.

What Causes Hairy Cell Leukemia?

Researchers do not know the exact cause of hairy cell leukemia. Scientists aren’t sure what risk factors make some people more or less likely to develop the abnormal hairy cells.

However, in almost every case of classic hairy cell leukemia, there is a genetic mutation in the cancer cells. This mutation is seen on the BRAFV600E gene in the cancer cells of classic HCL, although it is not present on variant forms of HCL. Treatment with BRAF inhibitors is often successful in achieving remission when a person with classic HCL has relapsed or is resistant to first-line treatments.

The overproduction of abnormal hairy cells causes a deficiency in all three of the main types of blood cells, which will show up on a complete blood count (CBC) test. This deficiency prevents healthy blood cells from doing their very important jobs:

• Red blood cells transport oxygen around the body.
• White blood cells help fight infection.
• Platelets help the blood clot and prevent excessive blood loss.

What Are the Symptoms of Hairy Cell Leukemia?

HCL symptoms usually come on slowly and gradually. These symptoms are also similar to those of several other conditions. Because of this, hairy cell leukemia can be overlooked or misdiagnosed by doctors who are not trained to recognize it. Some symptoms of hairy cell leukemia are:

• Feeling weak or tired (sometimes called “general malaise”)
• Getting sick more often and more easily
• Feeling full (due to enlarged spleen)
• Experiencing recurrent fevers
• Frequent infections
• Bruising or bleeding easily
• Losing weight for no reason
• Feeling pain in the left side of the stomach
• Lumps in the armpit, groin, neck, or stomach that are not painful
• Swelling in the lymph nodes

HCL cannot be diagnosed based on a person’s symptoms alone. Diagnosis of hairy cell leukemia usually comprises a series of blood tests and bone marrow tests. After conducting a physical exam, your doctor may order a complete blood cell and platelet count, bone marrow aspiration, and bone marrow biopsy.

Complications of HCL

People with HCL have compromised immune systems as a result of changes in their blood cells. This can make them more susceptible to infection — specifically, fungal infections and viruses that affect the liver, brain, lungs, and skin.

Up to one-third of people with HCL also have autoimmune diseases. Autoimmune disease can occur early in the disease process or at any time after diagnosis. Autoimmune complications in people with HCL may cause symptoms such as inflammation of the joints and blood vessels. This inflammation can result in joint pain, fever, skin rashes, swelling, or weight loss.

Treatment for Hairy Cell Leukemia

Because hairy cell leukemia is a type of chronic leukemia, it generally progresses very slowly and takes a longer time before it damages the body. It’s important to monitor HCL closely and regularly with your health care provider.

In many cases, people live with HCL for years without experiencing any symptoms or requiring treatment. A HCL diagnosis does not always mean starting treatment immediately. Your health care provider may take a “watch and wait” approach, also known as “active monitoring,” before deciding to initiate treatment.

The drugs used to treat HCL may cause side effects, such as kidney problems and immunosuppression. Treatments may also lower blood counts before they take effect and allow the body to produce more healthy blood cells — most importantly healthy white blood cells.

Chemotherapy

Chemotherapy with Cladribine or Nipent (pentostatin) is the first-line treatment for HCL. However, not everyone can be treated with chemotherapy. Around 10 percent of people do not respond to chemotherapy. Read more about chemotherapy for leukemia treatment.

Immunotherapy

Immunotherapy, or biologics, are used to treat HCL when first-line treatments fail or aren't appropriate. Biologics, including alpha interferon and immunoglobulin, work by using the body’s own immune system to fight the cancer cells.

Surgery

The spleen produces white blood cells. Removing the spleen, a splenectomy, used to be part of the standard treatment option for people with HCL. Today, only in rare instances is a splenectomy performed.

Clinical Trials

Depending on your circumstances, your doctor may recommend participating in a clinical trial. There are several treatments that are being tested for use in hairy cell leukemia, including Rituxan (rituximab). Rituxan is a targeted therapy used to treat several types of blood cancer. Participating in cancer research can expand the options available to you and contribute to greater scientific knowledge.

Prognosis

There currently is no cure for hairy cell leukemia, but it is treatable. The majority of people with HCL will undergo treatment eventually. However approximately 10 percent of all cases of HCL will not require treatment.

When treated with the chemotherapy drug Cladribine, around 85 percent people with HCL achieve complete remission. About 10 percent of people with HCL respond to Cladribine, but do not go fully into remission. People with HCL who undergo Cladribine treatment live event-free for five years approximately 90 percent of the time.

About 40 percent of people with HCL will relapse, sometimes after as long as a decade past the first round of successful treatment. Many will go back into remission after a second round of treatment.

If you have hairy cell leukemia, you are not alone. MyLeukemiaTeam is a community of people who, like you, are seeking support and shared experiences. Join today and find or make a supportive team of people living with leukemia.

Have you been diagnosed with hairy cell leukemia? Are you experiencing “watch and wait” monitoring with your health care provider? Do you have any insight for others undergoing treatment for HCL? Comment below or start a conversation on MyLeukemiaTeam.