I have been told that the "subset" here is the ID of CFIDS. Does anyone understand something in this? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3434293/ Chronic fatigue syndrome and subsequent risk of cancer among elderly U.S. adults Cindy M. Chang, Ph.D., M.P.H.,1 Joan. L. Warren, Ph.D.,2 and Eric A. Engels, M.D., M.P.H.1 1Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, MD 2Division of Cancer Control and Population Sciences, National Cancer Institute, Rockville, MD Address correspondence and reprint requests to: Cindy M. Chang, PhD, MPH, Infections and Immunoepidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, The publisher's final edited version of this article is available at Cancer See other articles in PMC that cite the published article. Abstract Background The cause of chronic fatigue syndrome (CFS) is unknown but is thought to be associated with immune abnormalities or infection. Because cancer can arise from similar conditions, we examined associations between CFS and cancer in a population-based case-control study among the U.S. elderly. Methods Using linked SEER-Medicare registry data, we evaluated ~1.2 million cancer cases and 100,000 controls (age 66–99 years, 1992–2005). CFS was identified in the period more than one year prior to selection using linked Medicare claims. We used unconditional logistic regression to estimate the odds ratios (ORs) comparing the CFS prevalence in cases and controls, adjusting for age, sex, and selection year. All statistical tests were two-sided. Results CFS was present in 0.5% of cancer cases overall and 0.5% of controls. CFS was associated with an increased risk non-Hodgkin lymphoma (NHL) (OR=1.29, 95% CI=1.16–1.43, p-value=0.0000017). Among NHL subtypes, CFS was associated with diffuse large B cell lymphoma (OR=1.34, 95% CI=1.12–1.61), marginal zone lymphoma (OR=1.88, 95% CI=1.38–2.57), and B-cell NHL not otherwise specified (OR=1.51, 95% CI=1.03–2.23). CFS associations with NHL overall and NHL subtypes remained elevated after excluding patients with medical conditions related to CFS or NHL, such as, autoimmune conditions. CFS was also associated (although not after multiple comparison adjustment) with cancers of the pancreas (OR=1.25, 95% CI=1.07–1.47), kidney (OR=1.27, 95% CI=1.07–1.49), breast (OR=0.85, 95% CI=0.74–0.98), and oral cavity and pharynx (OR=0.70, 95% CI=0.49–1.00). Conclusion Chronic immune activation or an infection associated with CFS may play a role in explaining the increased risk of NHL.