Natural history of diminutive and small colorectal polyps: a systematic literature review

Background and Aims: Diminutive (1-5 mm) and small (6-9 mm) polyps comprise 90% of detected lesions during colonoscopy and rarely contain advanced histology or colorectal cancer (CRC). Routine removal of these lesions results in a significant burden to colonoscopy programs. At the same time, the risk for progression of these polyps to CRC is unclear. We performed a systematic review to explore the natural history of diminutive and small colorectal polyps. Methods: We searched MEDLINE and EMBASE for studies investigating the natural history of colorectal polyps. Studies were considered eligible when they assessed patients with 1- to 9-mm polyps that were not treated with polypectomy and that underwent follow-up. We excluded studies in patients with inflammatory bowel disease, polyposis syndromes, and previously diagnosed CRC. We independently extracted study characteristics and evaluated CRC and advanced adenoma (size >= 10 mm, containing high-grade dysplasia or villous features) as outcome parameters. Results: Of 8775 retrieved studies, 9 studies with 721 patients were included that prospectively evaluated the evolution of 1- to 9-mm polyps. In 7 studies the average duration of observation was 2 to 3 years. There was only 1 study in which 1 small polyp might have progressed to cancer. Of 1034 adenomas sized 1 to 9 mm in those studies, 6% progressed to advanced adenomas over time. Conclusions: Based on this systematic review, it appears that some 1-to 9-mm adenomas progress to advanced adenomas within 2 to 3 years. No information on long-term CRC transition rates was found. Defining the biologic significance of these polyps is needed to balance between benefits and harm of polypectomy. (PROSPERO database registration number: CRD42016036577.)