Long Term Recurrence Following Wide Field Endoscopic Mucosal Resection (WF-EMR) for Advanced Colonic Mucosal Neoplasia Results of the Australian Colonic EMR (ACE) Multicenter Prospective Study of 940 Patients Alan Moss*, Stephen J. Williams, Luke F. Hourigan, Gregor J. Brown, Simon A. Zanati, Rajvinder Singh, William Tam, Karen Byth, Michael J. Bourke Gastroenterology, Westmead Hospital, Sydney, NSW, Australia; Endoscopy, Western Health, Melbourne, VIC, Australia; Gastroenterology, Princess Alexandra Hospital, Brisbane, QLD, Australia; Gastroenterology, The Alfred Hospital, Melbourne, VIC, Australia; Gastroenterology, The Epworth Hospital, Melbourne, VIC, Australia; Gastroenterology, Lyell McEwin Hospital, Adelaide, SA, Australia; Biostatistics, University of Sydney, Sydney, NSW, Australia WF-EMR is a comparatively new therapy for advanced mucosal neoplasia of the colon. It allows safe and effective removal of lesions up to 120mm in size (figure 1). Limited data is available regarding early (3-6 month) recurrence. Even less is known about late recurrence, defined as recurrence following a normal intervening colonoscopy and biopsy. Consequently, the optimal timing of surveillance colonoscopy following colonic WF-EMR is unknown. Previous studies are limited by small numbers, smaller lesions and/or retrospective design. This prospective, multicenter study conducted at 7 Australian academic endoscopy units aimed to quantify recurrence at 4 months and 12 months, and assess its clinical significance. Methods: The ACE study is an ongoing multicenter, prospective, intention to treat analysis of sessile colonic lesions 20mm in size or laterally spreading tumours (LSTs) referred for WF-EMR. Follow-up colonoscopy was performed in most patients at 4 months and 12 months with photographic documentation and biopsy of the scar. In the limited subgroup of patients with smaller lesions (20-25mm) in whom en bloc or 2-piece excision was achieved, 12-month surveillance alone was allowed. These cases were excluded from this analysis. Results: 940 patients were enrolled to date. EMR was attempted in 903, and was successful in 818 (91%). Of these 818, to date 523 have had follow up colonoscopy at 4 months. 423 (81%) had no recurrence at 4 months. Of these, 172 have undergone 12 month colonoscopy to date, of whom only 1 (0.6%) had a late recurrence. This was a 30mm sized tubulovillous adenoma of the rectum. 100 (19%) had recurrence at 4 months which was unifocal and diminutive in most cases, and treated endoscopically. Of these, 33 have undergone 12 month colonoscopy, of whom only 3 (9%) had persisting recurrence at 12 months. All 3 lesions were in the rectum or left colon, measured 80-120mm in size and were tubulovillous adenomas with high grade dysplasia. The recurrence was successfully treated endoscopically in 2 of 3 cases, but 1 required surgery for persisting recurrence in an inaccessible area. (Figure 2). Conclusions: Early recurrence occurs in 19% of colonic EMR cases, but is of little long term clinical significance, as this is successfully treated endoscopically in a single session in 91% of cases and in 2 sessions in 97%. Thus, the purported clinical significance of low recurrence rates conferred by alternative techniques such as ESD may be overstated in the context of the increased complexity and risks associated with ESD compared with EMR. Late recurrence is rare, occurring in 1% of cases where the interval colonoscopy is normal. Surveillance cannot be abandoned after 4 months, but a normal 4 month colonoscopy is reassuring. These results have implications for the timing of surveillance colonoscopy following EMR of large sessile lesions.