Structured Cap-assisted Margin Assessment Reduces Residual Neoplasia after Colorectal Polypectomy: A Prospective Multicentre Proof-of-Concept Study

Background and study aims Recurrence after endoscopic resection of medium-to-large non-pedunculated colorectal polyps remains common and varies substantially between operators. We evaluated a structured cap-assisted resection margin assessment (CARMA) protocol designed to standardise near-field inspection and margin clearance. Patients and methods Prospective multicentre study of 48 non-pedunculated colorectal polyps ≥10 mm (mean 22.2 mm) in 43 patients. Following conventional cold or hot snare resection, CARMA comprised structured cap-assisted near-field inspection with targeted cold-snare resection of margin abnormalities. Circumferential cold-snare resection (CS360) was performed for histologic validation. The primary outcome was immediate histology-confirmed residual neoplasia after standard resection and after CARMA. Secondary outcomes included recurrence at surveillance, adverse events and exploratory assessment of inter-operator variability. Results After conventional resection, CARMA identified histology-confirmed residual neoplasia in 24/48 polyps (50.0%, 95% CI 35.9–64.1%). Following CARMA-targeted resection, residual microscopic neoplasia persisted in 3/48 (6.3%, 95% CI 2.1–16.8%; McNemar p = 9.5 × 10−7). According to ESGE criteria (adenoma or sessile serrated lesion with dysplasia ≥20 mm), 24/46 non-cancer lesions would have met recommendations for margin ablation; among the remaining lesions, CARMA identified histology-confirmed residual in 12/22 (54.5%). At surveillance (median 6 months), no recurrence was observed (0/38; 95% CI 0–9.3%). In an exploratory inter-operator analysis, residual rates differed before CARMA (20.0% vs 57.9%) and appeared to converge after CARMA (0% vs 7.9%). No CARMA- or CS360-related adverse events occurred. Conclusions Structured cap-assisted margin inspection substantially reduced histology-confirmed residual neoplasia in this proof-of-concept study. These findings support evaluation of margin-focused inspection and clearance strategies in larger studies.