Hairy cell leukemia (HCL) is a rare form of cancer. It involves white blood cells called B lymphocytes. White blood cells protect the body from infection. HCL gets its name from the tiny hair-like projections that stick out of the surface of these cancer cells. Illness results from the build up of these cancer cells in the bone marrow and spleen.

White Blood Cells
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Cancer occurs when cells in the body become abnormal. They divide without control or order. Leukemia is cancer of the white blood cells and their parent cells. Leukemia cells do not function normally. In this case, they can not fight infections. This means that the person is more likely to become infected with viruses or bacteria. The cancerous cells also overgrow the bone marrow. This forces other normal cells, like platelets out. Platelets are needed to help the blood clot. As a result, people with leukemia may bleed more easily.

The exact cause of HCL is unknown, but it may be linked to a genetic mutation.