Hairy Cell Leukemia (HCL)

Hairy cell leukemia (HCL) is a cancer of the B cells that normally produce antibodies necessary to fight infection. These cells have threadlike projections that resemble hair under the microscope.


B lymphocytes, or hairy cells, accumulate in the blood, bone marrow, and spleen. As the lymphocytes increase, they suppress healthy cells, resulting in low blood counts.

As the number of oxygen-carrying red blood cells declines, patients may develop anemia, appearing pale, tired, or short of breath. A decline in platelets that normally help the blood clot may lead to easy bruising or bleeding. A decline in white blood cells puts patients at increased risk for infections that can sometimes be life-threatening.

Other symptoms include fevers, unexplained weight loss, and an enlarged spleen. The latter causes a feeling of fullness in the abdomen and may make it uncomfortable to eat more than a little at a time.

Some patients with HCL have few or no symptoms.


Hairy cells (named for the many irregular threadlike projections found in these cells) may or may not be present in the blood. After blood tests and a physical exam, a bone marrow sample or tissue biopsy may be taken to test for the presence of hairy cells.

After numbing the area—usually the back of the hip—physicians insert a needle into the bone to extract the marrow cells. They then examine those cells under a microscope and test them for certain genetic changes.

Risk Factors

Fewer than one in 10,000 people are diagnosed with HCL in the course of their lives. There are fewer than 2,000 cases diagnosed each year in North America and Western Europe combined.


Current chemotherapy treatments are very effective, particularly cladribine. Other options include rituximab, pentostatin, and interferon.

Sometime surgery (splenectomy) is helpful.