Abstract

Introduction: Colorectal cancer (CRC) is the third most common cancer worldwide. Age-appropriate CRC screening with colonoscopy provides two benefits: (1) early cancer detection; and (2) resection of premalignant colonic polyps. The principle of cancer chemoprophylaxis has been proposed as a possible synergistic approach to endoscopic colon cancer prevention. Patients with diabetes mellitus (DM) are at increased risk of CRC, compared to non-diabetics. Metformin, one of the most commonly used therapeutic agents used to treat type 2 DM has previously been studied as a potential chemoprophylactic agent against CRC, however, the results have been mixed. We investigate the impact of metformin use on the behavior of colonic polyp generation in a veteran population. Methods: We performed a retrospective observational study. Included were average-risk patients with at least two documented screening colonoscopies between 1997 and 2013 at the Veterans Affairs New York Harbor Healthcare System. Exclusion criteria were: family history of CRC; personal history of IBD; personal or family history of polyposis syndromes. Patient demographics (age, sex, race, ethnicity, body mass index) and colon polyp-specific data (number, histology, largest size) were collected via chart review. Comparative statistics were performed. Results: 1,344 patients were included in our analyses (190 had prescription for metformin prior to their index colonoscopy, 1,154 were non-users). Mean follow-up was 6.9 vs. 7.2 years, respectively. Baseline demographic characteristics are summarized in Table 1. At index colonoscopy, metformin users had fewer adenomatous polyps compared to non-users 1.16 vs. 1.68 (p = 0.0046). In follow-up, however, metformin users had a statistically significant a higher per-annum rate of adenoma generation 0.36 vs. 0.25 as well as higher per-annum rates of high-risk adenoma generation (defined as villous histology, high-grade dysplasia, and/or size > 1 cm). Conclusion: While metformin appeared to be protective against adenomatous polyps at time of index colonoscopy, metformin users demonstrated higher rates of per-annum adenoma generation, including high-risk adenomas. There were no differences in sessile serrated polyp generation at baseline or in follow-up. The effect of metformin use on colon polyp behavior should be further investigated with specific aim of assessing impact of timing of drug exposure on colon cancer chemoprophylaxis.248_A Figure 1 No Caption available.248_B Figure 2 No Caption available.

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