Diagnosis and Treatment of Chronic Lymphocytic Leukemia

Nizar Tannir, Michael Keating, and Susan O'Brien

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative disorder (LPD) characterized by a progressive accumulation of small mature-appearing, long-lived, and functionally defective lymphocytes in the blood and bone marrow, lymph nodes, and spleen. It is the commonest leukemia in the Western world and accounts for 30 percent of all adult leukemias. About 95 percent of CLL cases are of B-cell phenotype.1-3 In Asian countries such as China and Japan CLL represents only 5 percent of all leukemias with the T-cell phenotype predominating.4,5 These geographic and ethnic differences in incidence are most likely the result of genetic rather than environmental factors, as it has been observed that Japanese who settled in Hawaii do not have a higher incidence of CLL than native Japanese.6,7 Also, CLL is the only leukemia not associated with exposure to radiation.8 Population studies have not shown any evidence linking CLL to known occupational or environmental risk factors.9-11 Among leukemias, CLL has the strongest familial aggregation, with a two- to sevenfold higher prevalence among family clusters than in the general population.12-14 About 8,000 new cases are diagnosed in the United States each year, with a median age of 65 years and a male/female ratio 1.3:1.15,16 The incidence of CLL among Blacks is nearly equal to that among Whites.17

The exact cause of CLL is still unknown, as is the precise cell of origin. The normal counterpart of the typical CLL cell is the CD5+ B lymphocyte, which is present in the mantle zone of the secondary lymphoid follicle and in the peripheral blood in small numbers.18 The CD5 + B cells are the predominant B-cell population in fetal spleen and peripheral blood, and they also constitute 10 to 25 percent of normal adult B cells. These cells produce polyspecific antibodies, including autoreactive antibodies. The CLL lymphocytes express very low amounts of surface immunoglobulins (sIg). Such low amounts of sIgs are only observed in normal B lymphocytes that have been rendered anergic by interaction with self-antigen. It has been hypothesized that B-CLL is a malignancy of a marginal zone-based subpopulation of anergic self-reactive CD5+ B cells, which produce polyreactive natural autoantibodies.18,19

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