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 protrude from the surface of these cancer cells. Illness results from the accumulation of these cancer cells in the bone marrow and spleen.

White Blood Cells
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The exact cause of HCL is unknown.