Chronic lymphocytic leukemia: epidemiology and etiologic findings.

Important features of the descriptive epidemiology of chronic lymphocytic leukemia (CLL) are briefly reviewed including geographic and ethnic patterns, racial differences, age, sex, and other sociodemographic characteristics. Two case-control studies of CLL recently carried out by the authors in Baltimore, USA and Yorkshire, England are described. Selected findings from the two studies are presented and compared including familial occurrence of leukemia, lymphoma and other cancers; post medical history of subacute and chronic bacterial and viral infections, autoimmune diseases, allergic disorders, and surgical excision of lymphoid tissue; and prior medication use. The results are consistent with genetic predisposition although it is probable that environmental determinants are important in the etiology, given the substantial sporadic occurrence of CLL within families. Several of the findings also provide support for an association of CLL with preceding immune perturbation.