Risk of Advanced Adenoma, Colorectal Cancer, and Colorectal Cancer Mortality in People With Low-Risk Adenomas at Baseline Colonoscopy: A Systematic Review and Meta-Analysis.

Objectives: We conducted a systematic review and meta-analysis of the risk of advanced adenomas (AAs), colorectal cancer (CRC), and/or CRC-related death among individuals with low-risk adenomas (LRAs).

Methods: We searched PubMed and Embase for studies published between January 2006 and July 2015. Quality and strength of the evidence were rated using the Newcastle-Ottawa Scale (NOS) and the GRADE framework, respectively.

Results: Eleven observational studies (n=64,317) were included. A meta-analysis of eight cohort studies (n=10,139, 3 to 10 years' follow-up) showed a small but statistically significant increase in the incidence of AAs in individuals with LRAs compared with those with a normal baseline colonoscopy (RR 1.55 (95% CI 1.24-1.94); P=0.0001; I=0%). The pooled 5-year cumulative incidence of AA was 3.28% (95% CI: 1.85-5.10%), 4.9% (95% CI: 3.18-6.97%), and 17.13% (95% CI: 11.97-23.0%) for the no adenoma, LRA, and AA baseline groups, respectively. Two studies, which could not be pooled, showed a reduction in the risk of CRC in individuals with LRAs compared with the general population (standardized incidence ratio 0.68 (95% CI 0.44-0.99) at a median follow-up of 7.7 years and OR 0.4 (95% CI 0.2-0.6) at 3-5 years). One large retrospective cohort study found a 25% reduction in CRC mortality in individuals with LRAs compared with the general population (SMR 0.75 (95% CI 0.63-0.88) at a median follow-up of 7.7 years).

Conclusions: We observed a small but significant increase in the risk of AAs in people with LRAs compared with those with a normal baseline colonoscopy, but compared with the general population, people with LRAs have significantly lower risks of CRC and of CRC-related mortality.