New and Recurrent Colorectal Cancers After Resection: a Systematic Review and Meta-analysis of Endoscopic Surveillance Studies

Background & Aims: Outcomes of endoscopic surveillance after surgery for colorectal cancer (CRC) vary with the incidence and timing of CRC detection at anastomoses or non-anastomoses in the colorectum. We performed a systematic review and meta-analysis to evaluate the incidence of CRCs identified during surveillance colonoscopies of patients who have already undergone surgery for this cancer. Methods: We searched PubMed, EMBASE, SCOPUS, and the Cochrane Central Register of Clinical Trials through January 1, 2018 to identify studies investigating rates of CRCs at anastomoses or other locations in the colorectum after curative surgery for primary CRC. We collected data from published randomized controlled, prospective, and retrospective cohort studies. Data were analyzed by multivariate meta-analytic models. Results: From 2373 citations, we selected 27 studies with data on 15,803 index CRCs for analysis (89% of patients with stage I–III CRC). Overall, 296 CRCs at non-anastomotic locations were reported over time periods of more than 16 years (cumulative incidence, 2.2% of CRCs; 95% confidence interval [CI], 1.8%–2.9%). The risk of CRC at a non-anastomotic location was significantly reduced more than 36 months after resection compared with before this time point (odds ratio for non-anastomotic CRCs at 36–48 months vs 6–12 months after surgery, 0.61; 95% CI, 0.37–0.98; P =.031); 53.7% of all non-anastomotic CRCs were detected within 36 months of surgery. One hundred and fifty-eight CRCs were detected at anastomoses (cumulative incidence of 2.7%; 95% CI, 1.9%–3.9%). The risk of CRCs at anastomoses was significantly lower 24 months after resection than before (odds ratio for CRCs at anastomoses at 25–36 months after surgery vs 6–12 months, 0.56; 95% CI, 0.32–0.98; P =.036); 90.8% of all CRCs at anastomoses were detected within 36 months of surgery. Conclusions: After surgery for CRC, the highest risk of CRCs at anastomoses and at other locations in the colorectum is highest during 36 months after surgery—risk decreases thereafter. Patients who have undergone CRC resection should be evaluated by colonoscopy more closely during this time period. Longer intervals may be considered thereafter.