Epidemiology of Chronic Lymphocytic Leukemia in Sardinia, Italy (1974-2003)

Several reports have described a worldwide increasing incidence of chronic lymphocytic leukemia (CLL) dating back seven to eight decades. Although genetic susceptibility would be an implausible explanation, the determinants of this upward trend and its spatial coordinates are poorly understood. We explored CLL incidence in Sardinia, Italy, using a validated database including the 1700 CLL cases diagnosed during 1974-2003. We applied Bayesian methods to map the CLL probability by administrative unit and Poisson regression analysis to investigate socioeconomic and environmental determinants adjusting by possible confounders. The standardized (Standard European population) incidence rate for the Sardinian population over the study period was 5.1 per 100,000 (95% confidence interval [CI] 4.9-5.3), increased annually by 5.8% (95% CI 5.7-6.0) consistently by sex and age, and was more noticeable in urban areas. Five administrative units exceeded the 95% posterior probability of an elevated CLL incidence: these were rural areas spread over the regional territory, not suggestive of spatial clustering. The Poisson regression analysis showed that the risk was elevated in urban areas (RR = 1.11, 95% CI 1.05-1.17), among residents ≥ 30 km from the nearest hospital (RR = 1.09, 95% CI 1.06-1.12), and with the local prevalence of cork harvesting (RR = 1.62, 95% CI 1.12-2.34). Our results suggest that better access to health care facilities and improvements in diagnostic efficacy might have generated the observed upward trend in CLL incidence, along with contributing environmental factors.