Abstract
BackgroundIncreasing evidence suggests that a history of diabetes mellitus (DM) may be associated with an increased risk of bladder cancer. We performed a systematic review with meta-analysis to explore this relationship.MethodsWe identified studies by a literature search of Medline (from 1 January 1966) and EMBASE (from 1 January 1974), through 29 February 2012, and by searching the reference lists of pertinent articles. Summary relative risks (RRs) with corresponding 95% confidence intervals (CIs) were calculated with a random-effects model.ResultsA total of 36 studies (9 case–control studies, 19 cohort studies and 8 cohort studies of patients with diabetes) fulfilled the inclusion criteria. Analysis of all studies showed that DM was associated with an increased risk of bladder cancer (the summary RR = 1.35, 95% CI 1.17–1.56, p < 0.001, I2 = 94.7%). In analysis stratified by study design, diabetes was positively associated with risk of bladder cancer in case–control studies (RR = 1.45, 95% CI 1.13-1.86, p = 0.005, I2 = 63.8%) and cohort studies (RR = 1.35, 95% CI 1.12-1.62, p < 0.001, I2 = 94.3%), but not in cohort studies of diabetic patients (RR = 1.25, 95% CI 0.86–1.81, p < 0.001, I2 = 97.4%). The RRs of bladder cancer were 1.38 (1.08-1.78) for men and 1.38 (0.90-2.10) for women with diabetes, respectively. Noteworthy, the relative risk of bladder cancer was negatively correlated with the duration of DM, with the higher risk of bladder cancer found among patients diagnosed within less than 5 years.ConclusionsThese findings support the hypothesis that men with diabetes have a modestly increased risk of bladder cancer, while women with diabetes were not the case.
Highlights
Increasing evidence suggests that a history of diabetes mellitus (DM) may be associated with an increased risk of bladder cancer
We examined whether the association between a history of DM and the risk of bladder cancer differs according to various study characteristics
To explore the potential heterogeneity between studies, we conducted analyses stratified by study design, gender, geographic region, publication year, and we evaluated the impact of adjustment for age, sex, smoking, alcohol consumption, body mass index (BMI),physical activity on the association between diabetes and the risk of bladder cancer
Summary
Increasing evidence suggests that a history of diabetes mellitus (DM) may be associated with an increased risk of bladder cancer. The relationship between DM and malignancies has been investigated extensively; and ample evidence indicates that individuals with diabetes have increased risk of several malignancies, including cancers of the colon and rectum [6]. A previous meta-analysis of 16 studies (7 case–control studies, 3 cohort studies and 6 cohort studies of patients with diabetes) conducted in 2006 showed that diabetes was associated with an increased risk of bladder cancer in case–control studies and cohort studies, but not in cohort studies of patients with diabetes. A publication bias against studies with small sample sizes and against reporting a low relative risk is possible, and may have resulted in an overestimation of the relationship between diabetes and bladder cancer [7]. The association in different gender groups is worthy of investigation, but has not been looked at
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