Chapter 131:  Hairy Cell Leukemia

Hairy cell leukemia, a malignant lymphoproliferative disease of B-cell origin, was first described in the United States in 1958 and was referred to initially as leukemic reticuloendotheliosis.¹ By the mid-1970s, it had become a more easily recognized disease, characterized by splenomegaly and pancytopenia without lymphadenopathy.^2–8 Peripheral blood smears showed a low percentage of abnormal mononuclear cells with irregular cytoplasmic projections. These cells were present in many organs but were of pathophysiologic significance in their presence in the bone marrow and spleen. The disease constitutes approximately 2% of the adult leukemias, which suggests there are approximately 1,000 new cases diagnosed per year in the United States.

Although splenectomy was the indicated treatment in the 1970s to correct the effects of hypersplenism, by the early 1980s, recombinant interferon (IFN)-α was shown to be effective systemically. By the mid-1980s, the adenosine deaminase (ADA) inhibitor deoxycoformycin (pentostatin) was found to induce a higher percentage of complete responses than did IFN. In 1990, a deoxyadenosine analog, 2-chlorode-oxyadenosine (cladribine), was shown to induce lasting clinical complete remissions with few residual hairy cells in the bone marrow after a single 7-day continuous intravenous (IV) infusion of the drug. Currently, the disease has an extremely favorable prognosis with the use of various intermittent therapies. It is well controlled but probably still not curable.