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Review
. 2011 Nov;106(11):1911-21; quiz 1922.
doi: 10.1038/ajg.2011.301. Epub 2011 Sep 13.

Is diabetes mellitus an independent risk factor for colon cancer and rectal cancer?

Hiroki Yuhara  1 , Craig Steinmaus, Stephanie E Cohen, Douglas A Corley, Yoshihiro Tei, Patricia A Buffler
Affiliations
Review

Is diabetes mellitus an independent risk factor for colon cancer and rectal cancer?

Hiroki Yuhara et al. Am J Gastroenterol. 2011 Nov.

Abstract

Objectives: Diabetes mellitus (DM) has been associated with an increased risk of colorectal cancer (CRC). The American College of Gastroenterology Guidelines for Colorectal Cancer Screening 2008 recommend that clinicians be aware of an increased CRC risk in patients with smoking and obesity, but do not highlight the increase in CRC risk in patients with DM. To provide an updated quantitative assessment of the association of DM with colon cancer (CC) and rectal cancer (RC), we conducted a meta-analysis of case-control and cohort studies. We also evaluated whether the association varied by sex, and assessed potential confounders including obesity, smoking, and exercise.

Methods: We identified studies by searching the EMBASE and MEDLINE databases (from inception through 31 December 2009) and by searching bibliographies of relevant articles. Summary relative risks (RRs) with 95% confidence intervals (CIs) were calculated with fixed- and random-effects models. Several subgroup analyses were performed to explore potential study heterogeneity and bias.

Results: DM was associated with an increased risk of CC (summary RR 1.38, 95% CI 1.26-1.51; n=14 studies) and RC (summary RR 1.20, 95% CI 1.09-1.31; n=12 studies). The association remained when we limited the meta-analysis to studies that either controlled for smoking and obesity, or for smoking, obesity, and physical exercise. DM was associated with an increased risk of CC for both men (summary RR 1.43, 95% CI 1.30-1.57; n=11 studies) and women (summary RR 1.35, 95% CI 1.14-1.53; n=10 studies). For RC, there was a significant association between DM and cancer risk for men (summary RR 1.22, 95% CI 1.07-1.40; n=8 studies), but not for women (summary RR 1.09, 95% CI=0.99-1.19; n=8 studies).

Conclusions: These data suggest that DM is an independent risk factor for colon and rectal cancer. Although these findings are based on observational epidemiological studies that have inherent limitations due to diagnostic bias and confounding, subgroup analyses confirmed the consistency of our findings across study type and population. This information can inform risk models and specialty society CRC screening guidelines.

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Conflict of interest statement

CONFLICT OF INTEREST

Guarantor of the article: Hiroki Yuhara, MD, MPH.

Specific author contributions: H.Y. and C.S. participated in study design and drafted the manuscript. C.S. helped to establish protocols for study selection, and methods for the statistical analysis of data and assisted in quality control procedures and publication writing. S.E.C. assisted in publication writing. H.Y. and S.E.C. performed the statistical analysis. S.E.C., P.A.B., Y.T., and D.A.C. critically revised the manuscript. All authors read and approved the final manuscript.

Potential competing interests: None.

Figures

Figure 1
Figure 1
Flowchart of meta-analysis.
Figure 2
Figure 2
Association between diabetes and colon cancer (CC) incidence in six case–control and eight cohort studies. AC, ascending colon; C, cecum; CI, confidence interval; DCC, distal colon cancer; ES, effect size; m, men; PCC, proximal colon cancer; w, women.
Figure 3
Figure 3
Association between diabetes and rectal cancer (RC) incidence in six case–control and eight cohort studies. CI, confidence interval; m, men; w, women.
Figure 4
Figure 4
Funnel plot with pseudo 95% confidence limits.
See this image and copyright information in PMC

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