The incidence of chronic lymphocytic leukemia in Taiwan, 1986-2005: a distinct increasing trend with birth-cohort effect.

The incidence of chronic lymphocytic leukemia (CLL) in Taiwan is markedly lower than that in Western countries, but we have seen a drastically increasing trend. We explored this distinct incidence trend of CLL for Taiwanese. The epidemiologic data of CLL for Taiwanese and Caucasian Americans during 1986 to 2005 were obtained from the Taiwan National Cancer Registry and Surveillance, Epidemiology, and End Results Program, respectively. The individual effects of time period and birth cohort on the incidence trends were analyzed using an age-period-cohort model. Although there was a weak period effect corresponding to the increased applications of immunophenotyping in 1991 to 1995 in Taiwan, evidences suggested that the age-adjusted incidence rate of CLL for Taiwanese was continuously increasing during the 20-year period while that for Caucasian Americans remained steady. In addition, a much stronger birth-cohort effect was identified for Taiwanese but not for Caucasian Americans. This effect corresponded to the westernization of lifestyle in Taiwan since 1960. We conclude that, in addition to the ethnic difference of incidence, there is distinct increasing incidence trend of CLL in Taiwan. The strong birth-cohort effect underlying this increasing trend indicates that lifestyles and environmental factors may play a role in the development of CLL for Taiwanese.