Proximal polyps are associated with higher incidence of colorectal cancer: Analysis of the Minnesota Colon Cancer Control Study.

Background: Despite reports indicating that polyps proximal to the splenic flexure have higher rates of metachronous colorectal adenocarcinoma (CRC), the role of adenoma location on surveillance recommendations remains unclear. This study aimed to analyze the association between index polyp location and post-colonoscopy CRC among participants of the Minnesota Colon Cancer Control Study (MCCCS).

Methods: The MCCCS randomized 46,551 patients 50-80 years to usual care, annual, or biennial screening with fecal occult-blood testing (FOBT). Screening was performed between 1976-1992. Positive FOBT was followed by colonoscopy. We analyzed participants whose colonoscopy revealed at least one adenoma. Patients were divided into those with at least one lesion proximal to the splenic flexure and those without.

Results: Of 2,295 patients, 815 had proximal adenomas. The majority were men; mean age =62 years at randomization, and 69 years at index polyp. There was a high rate of advanced adenomas: 44% ≥1 polyp ≥1 cm, 35% with villous histology, and 5% high grade dysplasia. At 20 years, 87 patients had a CRC diagnosis, and the estimated cumulative incidence of CRC was 4.3%. Proximal adenomas had a higher risk of developing a post-colonoscopy CRC (SHR=1.63, 95% CI=1.05-2.53, P=0.03), which was attenuated after adjusting for polyp multiplicity in sensitivity analyses (SHR=1.56, 95% CI=0.96-2.53, P=0.07).

Conclusion: Although patients with proximal adenomas were found to have higher hazards of post-colonoscopy CRC, adjusting for polyp multiplicity attenuated the strength of association. Further research is warranted to determine whether polyp location should be factored in the determination of appropriate surveillance intervals.