Hairy cell leukemia (HCL) is a rare chronic leukemia in adults. Around 1,000 people in the United States develop HCL each year, according to the World Health Organization. The average age at diagnosis is 52. HCL is more common in men than in women. There is no clear evidence that HCL runs in families or is caused by specific environmental factors.

The disease is called hairy cell leukemia because the leukemia cells have long thin projections that look like hairs.

Symptoms of Hairy Cell Leukemia

Some people with HCL do not have any symptoms. For them, HCL is typically diagnosed during an evaluation for a low blood count. Among those who do have symptoms, the most common causes are an enlarged spleen and a low blood count.

An enlarged spleen doesn’t always cause symptoms. However, when it does, they may include pain on the left side of the abdomen that can spread to the left shoulder or a feeling of being full for no reason (for example, after eating only a few bites of a meal).

Common signs of a low blood count (a shortage of normal blood cells) can include the following:

• fevers
• frequent infections
• fatigue
• loss of appetite
• easy bruising or bleeding

Diagnosis of Hairy Cell Leukemia

Doctors do a variety of tests to diagnose HCL. These include blood tests and bone marrow tests. Some of these tests look for specific features of the leukemia cells to confirm the diagnosis and determine how advanced the HCL is. Occasionally, imaging tests (a CT scan or an ultrasound) may be needed to study the spleen. Because it is rare, HCL is not always easy to diagnose. Sometimes it takes the experience of someone who’s skilled in identifying hairy cell leukemia to arrive at an accurate diagnosis.

Specialized testing of the genetics of the leukemia cells may be helpful in diagnosis and treatment. For example, mutations in a gene called BRAF are found in the leukemia cells of most people with HCL. The results of these diagnostic tests help doctors create a personalized treatment plan.

The recommended treatments for HCL vary. People who don’t have symptoms or a low blood count may be observed for any changes during regular office visits and with laboratory tests. For those who need treatment, the typical goals are to restore a normal blood count and, if needed, to reduce the spleen size.

Learn more about treatment for hairy cell leukemia

Ongoing Care

People with HCL are likely to have regular checkups. Their doctor will monitor the disease and determine if it is growing. These visits may include a physical exam, blood tests, bone marrow aspirates, biopsies, and radiographic studies.