Epidemiology

CLL is the most common adult form of leukemia in Western society. According to a recent analysis of the Surveillance Epidemiology and End Results database,1 the annual overall age-adjusted incidence in the United

States between 1997 and 2001 was 3.5/100,000 people: 5.0/100,000 for males and 2.5/100,000 for females. This is a disease of older adults with distinct and unique clinical characteristics and concerns. The majority of individuals are diagnosed when over 65 years of age, and the incidence increases with increasing age. The incidence for individuals over age 70 years is 50/100,000. The median age at diagnosis between 1997 and 2001 was 72 years: for males 70 years and 74 years of age for females. This median has risen over the past 10-15 years, likely due to aging of the U.S. population. The 5-year survival (1995-2000) was 73% overall: 71% for males and 76% for females. The median age at death was 78 years: 76 for males and 81 years for females.

In the United States, CLL is most common in the Caucasian population and less common in African-Americans and individuals from the Far East. The age-adjusted annual incidence between 1975 and 2001 for Caucasians was 3.9/100,000 and for African-Americans 2.8/100,000.1 CLL is rare in individuals of Japanese ancestry.

Ghia et al. screened blood from 500 unselected healthy individuals over age 65 and identified a population of monoclonal (by light-chain analysis) CD5+/19+/23+ B cells in 3.8% of these individuals.2 These asymptomatic individuals did not have lympho-cytosis or clinical evidence of disease, and did not fulfill diagnostic criteria for CLL. Whether or not some or all of these individuals will progress to fulfill diagnostic criteria or develop symptomatic disease is unclear. Nevertheless, this indicates that the incidence of a monoclonal lymphoproliferative process is potentially much more common in the elderly population than has been previously appreciated.

The demographics of newly diagnosed patients are different today than 20 years ago. Due to the widespread availability of routine automated blood counts, a large proportion of patients is diagnosed based on incidental finding of lymphocytosis in the absence of any significant symptoms. These patients are therefore being diagnosed at an earlier stage. The overwhelming majority of patients present to private practice physicians and are followed and treated in this setting. Patients followed and treated at tertiary referral centers tend to be younger and more heavily pretreated. The median age for both previously untreated and previously treated patients on clinical trials at such institutions is roughly 60 years of age.

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