Rassmussen M-L H et al. – While causality could not be established in the present study, an intriguing positive long-term association between antibiotic use and CLL/SLL risk was observed.

• The aim of this study was, in a cohort design, based on the unique nationwide Danish registers, to investigate the association between use of antibiotics and the risk of NHL subtypes.
• Based on the Civil Registration System, we established a cohort of the entire adult (?15y) Danish population. Information on use of antibiotics came from the Danish Drug Prescription Registry and lymphoma diagnosis from the Danish Cancer Registry.

• In total, 13,602 patients were diagnosed with one of the NHL subtypes during 51.6 million person-years of follow-up (1995-2008).
• We observed positive associations between use of antibiotics and plasma cell myeloma (PCM) (RR=1.11, 95% confidence intervals (CI)=1.00 to 1.24), chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) (RR=1.32, 95% CI=1.20 to 1.45), mantle cell lymphoma (MCL) (RR=1.40, 95% CI=1.04-1.88) and anaplastic large T-cell lymphoma (ALCL) (RR=1.83, 95% CI=1.00 to 3.36).
• Among these, the increased risk of CLL/SLL, MCL and ALCL, respectively, did not vary by years since use, and only the risk of CLL/SLL risk differed by number of prescriptions.