Likelihood of missed and recurrent adenomas in the proximal versus the distal colon

BackgroundColonoscopy may be less efficacious in reducing colorectal cancer mortality in the proximal compared with the distal colon. A greater likelihood for missed and recurrent adenomas in the proximal colon may contribute to this phenomenon.ObjectiveTo examine whether a proximal adenoma is associated with the risk and location of missed and recurrent adenomas.DesignProspective.SettingPolyp Prevention Trial.ParticipantsA total of 1864 patients with an adenoma at baseline underwent a follow-up colonoscopy 4 years later (adenoma recurrence). Of these, 1731 underwent a clearing colonoscopy 1 year after the baseline examination (missed adenoma).Main Outcome MeasurementsAssociation of baseline adenoma location with the risk and location of adenomas found at colonoscopy performed 1 year and 4 years later.ResultsAt the year 1 colonoscopy, 598 patients (34.6%) had an adenoma (missed adenoma). Compared with those with a distal-only adenoma at baseline, patients with a proximal-only adenoma at baseline were more likely to have any missed adenomas (relative risk [RR] 1.28; 95% CI, 1.09-1.49) and a proximal-only missed adenoma (RR 2.05; 95% CI, 1.49-2.80). At the year 4 colonoscopy, 733 patients (39.3%) had adenoma recurrence. Patients with a baseline proximal-only adenoma were more likely to have any adenoma recurrence (RR 1.14; 95% CI, 1.00-1.31) and a proximal-only adenoma recurrence (RR 1.52; 95% CI, 1.15-2.02). Sensitivity analyses involving missed adenomas did not materially affect the risk or location of recurrent adenomas at year 4 colonoscopy.LimitationLesions may still be missed on repeated colonoscopies.ConclusionsMissed and recurrent adenomas are more likely to be in the proximal colon.