The goal of this clinical trial is to clarify the role of adjuvant thermal ablation for non-thermal endoscopic mucosal resection (EMR) of large (≥20mm) flat colorectal polyps (so-called laterally spreading lesions [LSLs]).

The hypothesis is that adding adjuvant thermal ablation to non-thermal EMR (vs no ablation) will result in lower lesion recurrence rates at 6-month follow-up, and non-inferior adverse events (AE) rates 14 days post EMR.

For participants with planned EMR, endoscopists will perform non-thermal EMRs as per standard of care and:

• adjuvant thermal ablation will either not be performed (control group), or will be applied to the base and outside margins of the resection site (experimental group);
• then, all patients will be contacted 14-44 days after EMR, to verbally ascertain the occurrence of AEs;
• then, all patients will undergo a first follow-up colonoscopy at 6 months after initial conoloscopy to assess lesion recurrence;
• finally, all patients will undergo a second and final colonoscopy 18 months after EMR.

This trial is an open-label, two-arm, parallel-group, multicenter RCT with co-primary outcomes (superiority for recurrence, non-inferiority for AEs). Patients undergoing non-thermal EMR will be randomized (1:1) to adjuvant thermal ablation (experimental group) or no ablation (control group).

All participating endoscopists will view dedicated teaching videos of the standard thermal ablation technique and key technical details to ensure consistent study procedures. Patients with planned EMR procedures will be invited by a research assistant before the EMR to participate in the study. Patients will be randomized to control or experimental groups in a 1:1 ratio using a central REDCap randomization module after the EMR resection phase is completed and immediately before adjuvant thermal ablation (intervention). This will limit bias by ensuring that the EMR technique is not affected by group allocation. When 2 or more lesions are present in a patient, the largest lesion will be chosen for inclusion in the study and all lesions will be photodocumented for auditing purposes.

No ablation (control group): Non-thermal EMR will be performed as per standard of care with submucosal injection and non-electrocautery resection of all visually visible polyp tissue using a snare. When the endoscopist determines that the resection is complete, no adjuvant thermal ablation of the post-EMR defect will be performed. Defect closure using clips will be performed only if there is concern for injury to the muscle layer or signs of overt perforation. A tattoo will be placed 3 cm distal to the resected lesion to allow for better identification of the resection site for follow-up. If multiple large polyps are found and removed, the largest lesion (study polyp) will be marked with two tattoos 3 cm distally and 3 cm proximally, to clearly identify the study polyp resection site.

Adjuvant thermal ablation (experimental group): Non-thermal EMR will be performed as per standard of care with submucosal injection and non-electrocautery resection of all visually visible polyp tissue using a snare. When the endoscopist determines that the resection is complete, submucosal injection (0.9% NaCl with methylene blue solution) using the h-APC probe (ERBEJET 2 attached to Vio3 electrosurgical unit, pressure: 40 bar) will be performed to further expose the resection margin. Adjuvant thermal ablation will be applied to the outside margins of the resection site using the h-APC probe. Then, adjuvant thermal ablation will also be applied to the base of the resection site using the h-APC probe. The precise electrocautery mode (PRECISE-APC setting 9) will be used to apply thermal ablation, as previously described for h-APC. Defect closure using clips will be performed only if there is concern for injury to the muscle layer or signs of overt perforation. A tattoo will be placed in the same way as described in the control group and, again, if multiple large polyps are found and removed, the largest lesion (study polyp) will be marked with two tattoos 3 cm distally and 3 cm proximally, to clearly identify the study polyp resection site.

At 6 months after initial colonoscopy, patients will undergo a first follow-up colonoscopy, as suggested by current guidelines and from studies showing that most recurrences occurred within the first 6 months. A window of 3 to 13 months will be permitted for the first follow-up. If recurrence is detected, patients will undergo subsequent colonoscopies at shortened intervals, as determined by the treating endoscopist, until no recurrence is detected. If surgery is performed due to difficulty in treating recurrence, patients will undergo a follow-up colonoscopy 6 months after surgery to detect any possible recurrence. All patients will undergo a second and final study colonoscopy 18 months after randomization, which will also mark the end of study follow-up. The second follow-up may be conducted within a window of 14 to 24 months. Subsequent colonoscopies will then be recommended outside the study as per routine care for such a clinical situation.

Inclusion Criteria:

• Adult patients
• Undergoing EMR for large (≥20 mm) colorectal LSL
• Providing written and informed consent for study participation

Exclusion Criteria:

• Inflammatory bowel disease
• Non-elective colonoscopy
• Poor general health (American Society of Anesthesiologists classification >III)
• Coagulopathy or thrombocytopenia (international normalized ration ≥1.5 or platelets <50*10^9/L)
• Bulky lesions (granular mixed with ≥10mm module).

Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures and appendices).

Beginning 12 months and ending 36 months following article publication.

Proposals should be directed to daniel.von.renteln.med@ssss.gouv.qc.ca. To gain access, data requestors will need to sign a data access agreement.