BACKGROUND AND STUDY AIMS: Due to the greater risks of adverse events (AEs) and the lower rate of submucosal invasive cancer (SMIC), large proximal colonic polyps are frequently treated by piecemeal endoscopic mucosal resection (EMR) in the West. However, this implies the risk of surgery to radicalize non-curative endoscopic resection in case of early colorectal cancer (CRC). We evaluated procedure outcomes in patients undergoing ESD for proximal colonic lesions at risk of SMIC. PATIENTS AND METHODS: All consecutive patients with lesions at risk of SMIC proximal to splenic flexure referred for ESD at a tertiary center were prospectively included from 2019 to 2021. En bloc, R0, and curative resection rates were primary outcomes, while length of hospitalization, AEs, need for surgery due to AEs, and recurrence rates were secondary outcomes. RESULTS: A total of 116 patients (mean age: 68.4±10.91 years
men: 69.8%) were included. En bloc, R0, and curative resection rates were 84.5%, 78.4%, and 72.4%, respectively. T1 adenocarcinoma was reported in 25% of lesions (29/116). Eleven patients (9.5%) underwent secondary surgery due to non-curative resections
residual disease was found in one patient. Most frequent AE was intra-procedural perforation (9.9%)
no AE required surgery. Median follow-up was 36 months
three of 97 recurrences (3.1%) at 6 months and one of 85 recurrence (1.2%) at 36 months were reported, which were all endoscopically treated. CONCLUSIONS: In expert hands, ESD is effective and safe for proximal colonic lesions at risk of SMIC for the favorable balance between risk of AEs and benefit of avoiding unnecessary surgery, even for early CRC.