Risk of Colorectal Cancer and Cancer Related Mortality After Detection of Low-risk or High-risk Adenomas, Compared With No Adenoma, at Index Colonoscopy: A Systematic Review and Meta-analysis

BACKGROUND & AIMS: The risk of metachronous colorectal cancer (CRC) among patients with no adenomas, low-risk adenomas (LRAs), or high-risk adenomas (HRAs), detected at index colonoscopy, is unclear. We performed a systematic review and meta-analysis to compare incidence rates of metachronous CRC and CRC-related mortality after a baseline colonoscopy for each group. METHODS: We searched the PubMed, Embase, Google Scholar, and Cochrane databases for studies that reported the incidence of CRC and adenoma characteristics after colonoscopy. The primary outcome was odds of metachronous CRC and CRC-related mortality per 10,000 person-years of follow-up after baseline colonoscopy for all the groups. RESULTS: Our final analysis included 12 studies with 510,019 patients (mean age, 59.2 +/- 2.6 years; 55% male; mean duration of follow up, 8.5 +/- 3.3 years). The incidence of CRC per 10,000 person-years was marginally higher for patients with LRAs compared to those with no adenomas (4.5 vs 3.4; odds ratio [OR], 1.26; 95% CI, 1.06-1.51; I-2=0), but significantly higher for patients with HRAs compared to those with no adenoma (13.8 vs 3.4; odds ratio [OR], 2.92; 95% CI, 2.31-3.69; I-2=0) and patients with HRAs compared to LRAs (13.81 vs 4.5; OR, 2.35; 95% CI, 1.72-3.20; I-2=55%). However, the CRC-related mortality per 10,000 person-years did not differ significantly for patients with LRAs compared to no adenomas (OR, 1.15; 95% CI, 0.76-1.74; I-2=0) but was significantly higher in persons with HRAs compared with LRAs (OR, 2.48; 95% CI, 1.30-4.75; I-2=38%) and no adenomas (OR, 2.69; 95% CI, 1.87-3.87; I-2=0). CONCLUSIONS: The results of this systematic review and meta-analysis demonstrate that the risk of metachronous CRC and mortality is significantly higher for patients with HRAs, but this risk is very low in patients with LRAs, comparable to patients with no adenomas. Follow-up of patients with LRAs detected at index colonoscopy should be the same as for persons with no adenomas.