Chronic lymphocytic leukaemia and small lymphocytic lymphoma: overview of the descriptive epidemiology

Abstract

The 2001 World Health Organization classification scheme considers B‐cell chronic lymphocytic leukaemia (CLL) and small lymphocytic lymphoma (SLL) in an aggregate category (CLL/SLL) because of shared clinicopathological features. We have estimated age‐adjusted incidence rates (IRs) of CLL and SLL in the population‐based Surveillance, Epidemiology and End Results Program in the United States to analyse patterns of CLL and SLL separately and jointly. Age‐standardized to the 2000 US population, overall IRs were 3·83 per 100 000 person‐years for CLL (n = 15 676) and 1·31 for SLL (n = 5382) during 1993–2004. Incidence of the combined entity, CLL/SLL, was 90% higher among males compared to females, and the male:female IR ratio was significantly higher for CLL (1·98) than for SLL (1·67). CLL/SLL IRs were 25% and 77% lower among Blacks and Asian/Pacific Islanders, respectively, compared to Whites. A significant reporting delay was evident for CLL but not for SLL, so that CLL/SLL temporal trends must be interpreted cautiously. CLL and SLL IRs increased exponentially with age among all gender/race groups, with CLL IRs increasing more steeply with advancing age than SLL. Avenues of future research include assessment of delayed‐ and under‐reporting to cancer registries and exploration of race, gender, and age effects in epidemiological studies.