Diabetes mellitus and incidence of kidney cancer: a meta-analysis of cohort studies

Diabetes is associated with increased risk of cancer at several sites, but its association with cancer of the kidney is unclear. We performed a systematic review with meta-analysis to examine the association between diabetes and incidence of kidney cancer. Pertinent studies were identified by searching PubMed (from January 1966 to December 2010) and reviewing the reference lists of relevant articles. We included cohort studies reporting RR estimates and 95% CI (or data to calculate them) of the association between diabetes and kidney cancer incidence. Summary RRs were calculated using a random-effects model. Nine cohort studies met the inclusion criteria. Analysis of all studies showed that compared with individuals without diabetes, patients with diabetes had a statistically significant increased risk of kidney cancer (RR 1.42, 95% CI 1.06-1.91). There was heterogeneity among studies (p < 0.001 for heterogeneity). The association was stronger in women (RR 1.70, 95% CI 1.47-1.97) than in men (RR 1.26, 95% CI 1.06-1.49). When restricting the analysis to studies that had adjusted for body mass index (n = 3) or cigarette smoking (n = 3), the RRs were 1.12 (95% CI 0.99-1.27) and 1.29 (95% CI 1.05-1.58), respectively. This meta-analysis indicates a positive association between diabetes and risk of kidney cancer. Future research should attempt to establish whether this association is causal.