Smoking, Lower Gastrointestinal Endoscopy, and Risk for Colorectal Cancer
Background: Lower gastrointestinal (GI) endoscopy can decrease colorectal cancer (CRC) risk strongly through detection and removal of adenomas. Thus, we aimed to investigate whether utilization of lower GI endoscopy modifies the effect of lifetime smoking exposure on CRC risk in a population-based case-control study. Methods: In this study from Southern Germany including 2,916 CRC patients and 3,044 controls, information about lifetime smoking and other risk factors was obtained from standardized interviews. Self-reported endoscopies were validated by medical records. Multivariate logistic regression was performed to investigate associations of smoking with CRC risk after stratification by utilization of lower GI endoscopy in the preceding 10 years. Results: Median age of patients and controls was 69 and 70 years, respectively. Former regular smoking was associated with increased CRC risk in the group with no previous endoscopy (adjusted odds ratio (OR) 1.50, 95% confidence interval 1.28-1.75), whereas no association was found in the group with preceding endoscopy (OR 1.05, 0.83-1.33; p for interaction <0.01). Lower GI endoscopy did not modify the association of smoking and CRC risk among current smokers and among the more recent quitters. Conclusions: Our results suggest that the increased risk of CRC among former regular smokers is essentially overcome by detection and removal of adenomas at lower GI endoscopy. However, risk of CRC was increased if smoking was continued into higher adult age. Impact: The strong protective effect of lower GI endoscopy may be compromised by continued smoking. Smoking cessation may increase the efficacy of lower GI endoscopy.