Hairy cell leukemia is a chronic and relatively 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. In the spleen, there is a characteristic location of these leukemic cells in the splenic red pulp. While lymph nodes in the abdomen may be involved, lymph nodes are rarely enlarged on physical examination. The original description of this malignancy included a number of patient cases that were reported in 1958.

For many years, the origin of this malignant cell was debated. It is now generally held that this is a malignant B cell that is found predominantly in the bone marrow and spleen. These cells do circulate in the blood as well.

This disease usually is gradual in onset. Patients present with fatigue, increased susceptibility to infection, and enlargement of the spleen. The malignant 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 500 new cases of this disease discovered every year in the United States. There is an unexplained larger number of men than women afflicted with this leukemia. This disease is treatable, but not curable. While the cause is not known, the treatment is usually very effective in helping patients lead a normal life.