Hairy cell leukemia is a chronic and rare form of adult leukemia. It is estimated that approximately 2 % of all adult patients with leukemia have this form of disease.

While the cause of this malignancy is not known, the origin of the malignant cell is thought to develop from the memory B cell compartment. These malignant cells infiltrate the bone marrow, the spleen, and the liver from the time of diagnosis. While lymph nodes in the abdomen may be involved, lymph nodes are rarely enlarged on physical examination.

Hairy cell leukemia is usually gradual in onset. Patients present with fatigue, increased susceptibility to infection, and enlargement of the spleen. The malignant hairy cells in the bone marrow compromise the usual production of normal red cells, white blood cells, and platelets that are manufactured in the bone marrow.

There are approximately 1,000 new cases of hairy cell leukemia discovered every year in the United States. There is an unexplained larger number of men than women afflicted with this leukemia. Hairy cell leukemia is treatable, but not curable. While the cause is not known, the treatment is usually very effective in helping patients lead a normal life.