Impact of Adenoma Size in Distal Colon on Risk for Advanced Adenoma of the Proximal Colon

Adenomas of the rectosigmoid colon are considered markers of risk for advanced adenomas of the proximal colon. However, studies report a wide variation in risk. This study was designed to determine the risk for advanced adenomas in the proximal colon in patients from a large, homogeneous population with an advanced or nonadvanced adenoma of the distal colon. We designed a prospective study of 7157 patients who were evaluated for neoplasia by flexible sigmoidoscopy and, when adenomas were found, by colonoscopy. Adenomas were considered advanced if they were ≥10 mm in size or had villous or dysplastic features. Ninety-seven patients had an advanced adenoma of the distal colon (Group A) and were compared with 183 patients who had a nonadvanced adenoma (Group B). Seven patients (7.2%) in Group A had an advanced adenoma of the proximal colon, compared with four patients (2.2%) in Group B (P < 0.05, relative risk = 3.3). When patients with adenomas of the distal colon >5 mm (Group C) were compared to patients with adenomas ≤5 mm (Group D), the prevalence of advanced adenomas of the proximal colon remained at 7% (10/143) for Group C but fell to 0.73% (1/137) for Group D (P = 0.011, relative risk = 9.6). By expanding the criteria for risk from adenomas of the distal colon to include all adenomas >5 mm, the relative risk for advanced adenoma of the proximal colon was increased threefold.