Hairy cell leukemia is a rare, slow-growing cancer of the blood in which the bone marrow produces too many B cells (lymphocytes), a type of white blood cell that fights infection. The condition is named after these excess B cells which look ‘hairy’ under a microscope because of fine projections (villi) from their surface. As the number of leukemia cells increases, fewer healthy white blood cells, red blood cells and platelets are produced.
Hairy cell leukemia affects more men than women, and it occurs most commonly in middle-aged or older adults. Hairy cell leukemia is considered a chronic disease because it may never completely disappear, although treatment can lead to a remission for years.