• Department of Epidemiology & Population Health, Stanford University School of Medicine, Stanford, CA, USA.
• Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA.
• Department of Medicine, University of Colorado Anschutz Medical Campus, Denver, CO, USA.
• Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA. berndts@mail.nih.gov.

Immune dysregulation is thought to contribute to chronic lymphocytic leukemia (CLL) risk, but biological mechanisms are unclear. We discovered that increased serum levels of B-cell activating factor (BAFF), an important regulator of B-cell maturation, were associated with a decreased risk of CLL, even >10 years after blood draw. Our findings suggest that BAFF could be a useful biomarker to assess risk among individuals at high risk, such as those with monoclonal b-cell lymphocytosis.