Colorectal endoscopic submucosal dissection (C-ESD) is a technically demanding procedure with a steep learning curve, especially in Western centers with limited access to foundational training. To fill training gaps, supervised trainee involvement has been suggested; however, there is still a dearth of data from Western institutions. This study aimed to evaluate the impact of supervised trainee involvement on C-ESD key outcomes.

This prospective, single-center study with an independent observer was conducted at Bordeaux University Hospital, France, and included 96 patients undergoing C-ESD between May 2024 and June 2025. Procedures were performed by two trainees under direct supervision (sESD group, n = 67) or by an expert endoscopist (eESD group, n = 29). Before starting supervised human cases, both trainees had completed preclinical training following the European Society of Gastrointestinal Endoscopy (ESGE) ESD curriculum. The rate of en bloc resection and clinically significant adverse events were the main outcomes. R0 resection, curative resection, procedure time, and dissection speed were evaluated as secondary outcomes. Subgroup analyses examined trainee involvement levels and procedural difficulty.

En bloc resection was accomplished in 100% of cases in both groups, despite the sESD group having considerably longer procedure times (75 vs. 43 minutes, p < 0.001) and slower dissection speeds (16 vs. 32 mm²/min, p = 0.003). The rates of curative resection and R0 resection were both high (95.5% vs. 96.6% and 97.0% vs. 100%, respectively; both p > 0.999). Although not statistically significant (p = 0.11), muscle injury rates were higher in the sESD group (25.4% vs. 10.3%). No perforations occurred in either group. Delayed bleeding was rare (2.1%) and equally distributed between groups. Shorter procedure times and easier cases were linked to higher trainee involvement.

Supervised trainee involvement in C-ESD is feasible and safe within a structured training program. Incorporating hands-on mentorship models into Western endoscopy training is supported by comparable resection quality and low complication rates.