{'fraction_non_alphanumeric': 0.025622518946228797, 'fraction_numerical': 0.018404907975460124, 'mean_word_length': 5.0524017467248905, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
ADTH-06 Microscopic residual lesion after apparent complete EMR of large lesions: evidence for mechanism of recurrence

Introduction Endoscopic mucosal resection (EMR) of large colorectal superficial neoplastic lesions (CSNL) is associated with significant recurrence and the risk of recurrence is significantly higher with piecemeal EMR (pEMR). The mechanism for recurrence has not been proven but has been postulated to occur as a result of microscopic areas of residual adenoma left between areas of sequential snare capture during pEMR. We aimed to determine the incidence of residual microadenoma in apparently normal mucosa left at the margin of the defect following EMR. Methods Following EMR/pEMR of 31 large CSNL, the base and margin of the resulting defect were examined with magnification chromoendoscopy and NBI/BLI to ensure complete resection. The apparently normal mucosa at the defect margin was then resected using the EndoRotor() device, removing and sampling the full extent of the defect margin. Areas of submucosal fibrosis or diathermy artefact at the base were also sampled if present. Data on the lesion characteristics, resection technique, number of pieces for pEMR, histopathology findings of the lesion and the mucosa at the margin were collected. Results Mean lesion size was 46.7 mm (range 32 mm-130 mm). Mucosa at the defect margin was sampled in all cases and 100% of the margin was achieved in 28 (90%). Final histopathology of resected lesions was adenoma in 27 (87%), serrated adenoma in 2 (6%) and adenocarcinoma in 2. Microscopic residual lesion was detected in the margin of apparently normal mucosa in 4 cases (13%). In 3 cases this was adenoma with low grade dysplasia and in one case a serrated lesion with no dysplasia was found in at the margin of a resected tubular adenoma. Microscopic residual lesion was detected in the base in 4 cases: 1 was microadenoma, 2 were serrated lesions without dysplasia in the base of resected adenomas and 1 was residual adenocarcinoma. There was no association with pEMR in >3 pieces and residual microscopic lesion or pEMR ≤3 pieces (OR 0.89, 95% CI 0.16–4.8, p=0.89). There were no complications. Conclusions To our knowledge, this is the first series examining the findings after continuous sampling of the full circumferential margin of apparently normal mucosa left at the defect after EMR of large CSNL. Despite examination with magnification suggesting complete resection, microscopic residual lesion at the margin was present in 13%. This study provides evidence that microscopic residual lesion left after EMR underlies the pathophysiology of recurrence and lends support for techniques that continuously resect or ablate the circumferential margin of the defect to reduce recurrence.