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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.

Albert Liu and colleagues report early experiences with uptake and delivery of pre-exposure prophylaxis(PrEP)for HIV prevention in three different settings in San Francisco. PrEP can be an important component of a comprehensive HIV prevention program and can complement efforts to increase HIV testing, linkage to care, and early initiation of antiretroviral therapy. Please see later in the article for the Editors' Summary