Hairy cell leukemia (HCL) is a rare chronic lymphoprolifer-ative disorder, which is characterized by circulating B lymphocytes displaying prominent cytoplasmic projections and infiltrating the bone marrow and spleen. Afflicted individuals are often elderly men who present with pancytopenia, splenomegaly, or recurrent severe infections. This disorder was first described as a distinct clinicopathologic entity in 1958 by Bourouncle et al.,1 who referred to the disorder as "leukemic reticuloendothe-liosis." The descriptive term "hairy cell leukemia" was coined by Schrek and Donnelly in 1966.2 During the past decade and a half the successful introduction of three effective systemic therapies—alpha-interferon, Pentostatin (2'-deoxycoformycin; dCF) and cladribine (2-chlorodeoxyadenosine; 2-CdA)—has dramatically and favorably altered the treatment options and prognosis for patients with this disease.


The precise incidence of HCL is unknown, but it is thought to account for 2 to 3 percent of all adult leukemias in the United States, with 600 new patients being diagnosed annually. The disease is particularly rare in Orientals and Blacks. It is predominantly a disease of middle-aged men with a median age at presentation of 52 years. There is a 4:1 male predominance, with Ashkenazi Jewish men being more frequently affected. The cause of HCL is unknown. Familial cases have been described.3 Early investigators described an association with HTLV-II, but later showed it was not directly related to the disease process.4 Prior exposure to radiation and organic solvents has been suggested to be more frequent among HCL patients.5,6

When cytogenetic analyses were performed in 30 patients with HCL, chromosome 5 was involved in clonal aberrations in 12 patients (40 percent) most commonly as trisomy 5 or pericentric inversions and interstitial deletions involving band 5q13.7 Hairy cell leukemia has been well characterized as a clonal B-cell disorder. The normal function and precise site of origin in the lymphocytic ontogeny of the hairy cell remains unknown but is believed to occur late in lymphocyte development, before the plasma cell.8 Macrophage colony-stimulating factor (M-CSF) induces hairy cell motility,9 and a specific integrin receptor, a,p3, has been identified that is responsible for their motility.10

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