Association Between Polyp Size and Malignant Invasion in Colorectal Polyps <20 mm: A Single-Trust Observational Study

Introduction Colorectal polyps are precursors to colorectal cancer. Accurate identification and follow-up of polyps during colonoscopy depend on reliable localization techniques, including tattooing. However, the optimal minimum polyp size threshold for routine tattooing remains poorly defined in current clinical guidelines. This study evaluated the association between polyp size and malignant invasion among colorectal polyps measuring smaller than 20 mm, with consideration of its implications for lesion localization and tattooing. Methods A retrospective observational study was conducted at Maidstone and Tunbridge Wells (MTW) NHS Trust. Data from 450 patients who underwent polypectomy of colorectal polyps < 20 mm during colonoscopy or flexible sigmoidoscopy between September 2021 and September 2022 were collected. One index lesion per patient was analyzed. In patients with multiple eligible polyps, the index lesion was selected according to a predefined hierarchy based on malignant invasion, dysplasia grade, size, and chronological order. Patients with polyps ≥ 20 mm and known hereditary colorectal polyposis syndromes were excluded. Chi-square tests were performed using SPSS version 25.0 (IBM Corp., Armonk, NY). Results A total of 450 participants were enrolled, including 288 (64.0%) male participants and 162 (36.0%) female participants. Polyp size distribution was 190 (42.2%) for 0-9 mm and 260 (57.8%) for 10-19 mm. Only 36 (8.0%) polyps were tattooed. Polyp locations included the right hemicolon in 134 patients (29.78%), transverse colon in 92 (20.4%), left hemicolon in 41 (9.1%), sigmoid colon in 128 (28.4%), and rectum in 55 (12.22%). Pedunculated polyps were identified in 143 patients (31.8%), whereas 256 (56.9%) had sessile polyps. Histologically, 251 polyps (55.8%) were tubular adenomas, and 349 (77.6%) exhibited low-grade dysplasia. Malignant invasion was detected in 27 patients (6%). Conclusion Malignant invasion was significantly more frequent in larger polyps within the <20 mm cohort. However, the low event rate among smaller lesions makes it difficult to define a reliable minimum size for tattooing. Larger prospective multicenter studies are therefore needed.