NEOPLASIA Brief report Respiratory tract infections and subsequent risk of chronic lymphocytic leukemia

Recent evidence suggests that chronic lymphocytic leukemia (CLL) might occur following a response to an infectious agent. We conducted a population-based study including 4249 CLL patients diag-nosed in Denmark from 1977 to 1997 and 15 690 frequency-matched controls to quantify risk of CLL following various airway infections. Through data linkage we gathered information on hospital inpa-tient/outpatient discharges that listed in-fections present at least 1 year prior to CLL. Using logistic regression, we calcu-lated odds ratios (ORs) and 95 % confi-dence intervals (CIs). Personal history of pneumonia was associated with signifi-cantly increased CLL risk (OR 1.4; 1.2-1.8); risk was restricted to 1 to 4.99 years prior to CLL diagnosis (OR 1.6; 1.2-2.0). Individuals with 3 or more prior pneumo-nia events had a significant 2.5-fold (1.1-5.6) elevated CLL risk, and risk increased with the number of pneumonia episodes (Ptrend<.001). None of 9 other respiratory-tract infections was significantly associ-ated with CLL risk. Pneumonia might be a potential CLL trigger or it could represent premalignant immune disruption preced-ing CLL. (Blood. 2007;109:2198-2201) © 2007 by The American Society of Hematolog