Incidence of microscopic residual adenoma after complete wide-field endoscopic resection of large colorectal lesions: evidence for a mechanism of recurrence

Background and Aims: EMR of large (>= 2 cm) nonpedunculated colorectal polyps (LNPCPs) is associated with high rates of recurrent/residual adenoma, possibly because of microadenoma left at the margin of resection. Data supporting this mechanism are required. We aimed to determine the incidence of residual microadenoma at the defect margin and base after EMR. Methods: We performed a retrospective observational study of patients undergoing EMR of large LNPCPs with the lateral defect margin further resected using the EndoRotor device (Interscope Medical, Inc, Worcester, Mass, USA) after confirming no visible residual adenomatous tissue. Aspects of the defect base were also resected in selected patients. Patients underwent surveillance at 3 to 6 months. Results: Resection of the normal defect margin was performed in 41 patients and of aspects of the base in 21 patients. Mean lesion size was 43.0 mm (range, 20-130). Microscopic residual lesion was detected in the margin of apparently normal mucosa in 8 cases (19%). In 7 cases this was an adenoma, and in 1 case a serrated lesion was found at the margin of a resected tubular adenoma. Microscopic residual lesion was detected at the base in 5 of 21 cases. Residual/recurrent adenoma was detected in 2 patients. Neither had residual microadenoma at the lateral margin or base detected after the primary resection. Conclusions: Microscopic residual adenoma after wide-field EMR was detected in 19% of cases at the apparently normal defect margin and at the resection base in 5 of 21 cases. This study confirms the presence of residual microadenoma after resection of LNPCPs, providing evidence for the mechanism of recurrence.