Abstract A28: Type 2 diabetes and risk of colorectal polyps in a colonoscopy-based study
Authors: Hardikar Sheetal , Burnett-Hartman Andrea N. , Cohen Stacey A. , Newcomb Polly A. 
Published: March 2017

Background: Type-2 diabetes mellitus (T2DM) and colorectal cancer (CRC) are both relatively common diseases among the adult population in the US; both diseases also share similar risk factors, including obesity, chronic inflammation, sedentary lifestyle, and selected dietary factors. Estimates suggest that 14% of CRC patients have T2DM as a comorbid condition at diagnosis. T2DM has also been identified as an independent risk factor for colorectal cancer. Most colorectal cancers arise from polyp precursor lesions, including advanced adenomas and a subset of serrated polyps, termed sessile serrated polyps. There is limited evidence regarding the association between T2DM and specific subtypes of colorectal polyps. We investigated the relationship between T2DM and the risk of subsets of colorectal polyps in a colonoscopy-based study in western Washington State.

Methods: Study participants were a subset of 20-79 year-old enrollees at Group Health, a population-based integrated health care system in the greater Puget Sound area in Washington State, who underwent a colonoscopy for any indication from 1998-2007. Eligible study participants completed a structured questionnaire to collect risk factor information, including self-report of clinically-diagnosed diabetes, and whether it was treated with medications. Participants were diagnosed as having adenomas (n=633), serrated polyps (n=602), synchronous presence of both adenomas and serrated polyps (n= 244) or as polyp-free controls (n=1052) on the basis of a standardized pathology review. Multivariable polytomous logistic regression was used to compare case groups with polyp-free controls and other case groups. Odds ratios (OR) and 95% confidence intervals (CI) were estimated, overall and by subtype, adjusted for age, sex, race, educational status, body mass index, smoking, alcohol intake, aspirin and nonsteroidal anti-inflammatory drug use, physical activity, history of previous endoscopy, and diet (fruits, vegetables and red meat intake).

Results: About 10% of the study population reported a history of clinically diagnosed T2DM, and 77% of those with T2DM took anti-diabetic medications. T2DM was not associated with the risk for colorectal polyps overall (adjusted OR 0.84; 95% CI 0.61-1.15). When evaluated by polyp subtype, T2DM diagnosis was not associated with the risk for adenomas (adjusted OR 1.02; 95% CI 0.70-1.48), but it was inversely associated with the risk for serrated polyps (adjusted OR 0.61, 95% CI 0.40-0.95). There was significant heterogeneity between adenomas and serrated polyps for their association with T2DM (P for heterogeneity=0.0001); however, the associations did not vary by lesion severity within each polyp subtype (advanced vs. non-advanced adenomas, sessile serrated vs. hyperplastic polyps). Also, associations did not differ statistically significantly between treated and non-treated diabetics for either adenomas or serrated polyps, but there was an increased risk for polyps overall among those not taking anti-diabetic medications (adjusted OR 1.26; 95% CI 0.63-2.53). This association was suggestive but did not reach statistical significance.

Conclusions: We observed that the risk for serrated polyps was significantly lower among those with a history of diabetes, while there was no observed association between colorectal adenomas and T2DM. This differential association may possibly be due to a variable effect of anti-diabetic medications on serrated pathway lesions, as suggested by the increased risk for polyps among untreated diabetics. Further studies are needed to better understand the mechanistic processes through which diabetes and its treatment may be differentially associated with the development of adenomas and serrated polyps.

Citation Format: Sheetal Hardikar, Andrea N. Burnett-Hartman, Stacey A. Cohen, Polly A. Newcomb. Type 2 diabetes and risk of colorectal polyps in a colonoscopy-based study. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr A28.