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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The exact cause of HCL is unknown.