Randomized Comparison of Surveillance Intervals after Polypectomy: Results from the Japan Polyp Study

National Polyp Study (NPS) recommended an interval of at least 3 years between colonoscopic removal of all adenomatous polyps and surveillance colonoscopy. However, the study was conducted prior to the recent studies documenting the importance of nonpolypoid lesions. The aim of this study was to assess whether follow-up colonoscopy at 3 years as well as at both 1 and 3 years would detect clinically important lesions. Japan Polyp Study, a multicenter RCT was initiated in 2003. Patients were eligible if they have had two colonoscopies with removal of all neoplasms. Following this they were randomly assigned to have follow-up colonoscopy at 1 and 3 years (two-exam) or at 3 years (one-exam group). Index lesions (ILs) were defined as any LGD >10 mm, HGD or cancer. 3926 patients mean age 57.3 years, consented to participate in this study. Of these, 2166 patients were randomly assigned into two groups (1087 to two-exam and 1079 to one-exam group). The results of non-inferiority test were significant (p=0.017 in per-protocol, p=0.001 in intention-to-treat). In per-protocol analysis (701 in two-exam vs 763 in one-exam), the IL incidences of two groups were similar (1.7% vs 2.1%). Colonoscopy performed 3 years after removal of all neoplasms detected important lesions as effectively as follow-up colonoscopy after both 1 and 3 years, being such results in accordance with those of the NPS.