Diabetes and kidney cancer: A direct or indirect association?

Abstract

A positive association between diabetes and kidney cancer has been reported in several investigations, but it is unclear whether diabetes or its complications account for this association. Recent advances in estimating direct associations may be useful for elucidating the association between diabetes and kidney cancer. Therefore, we performed a case-control analysis to evaluate whether the direct association between diabetes and kidney cancer is the primary concern in this exposure-outcome relation. Discharge data (with International Classification of Diseases – 9 codes) from 2001 for hospitals throughout Florida were used to construct a case-control population of inpatients aged ≥45 years. Cases (n=1,909) were inpatients with malignant kidney cancer and controls (n=6,451) were inpatients with motor vehicle injuries. Diabetes status was ascertained for cases and controls. Covariates that required adjustment to estimate the total (age, gender, ethnicity, obesity, and smoking) and direct (age, gender, ethnicity, obesity, smoking, hypertension, and kidney disease) associations were identified in a directed acyclic graph. Binary logistic regression was used to estimate the adjusted total and direct odds ratios (ORs) and corresponding 95% confidence intervals (CIs) of kidney cancer for diabetics. The odds of kidney cancer were higher for inpatients with diabetes than inpatients without diabetes when estimating the total association (OR=1.27, 95%CI: 1.10, 1.47) but attenuated when estimating the direct association (OR=1.08, 95%CI: 0.93, 1.25). Our findings provide preliminary insight that the direct association between diabetes and kidney cancer may not be the primary concern in this exposure-outcome relation; indirect pathways (i.e. diabetic complications) may have greater influence on this relation. A similar analysis using longitudinal data with appropriately measured covariates may provide more definitive conclusions and could have implications for kidney cancer prevention among diabetics